Laboratory Safety Incidents: Explosions 

     Centrifuge Explosions

       Unapproved Rotor Explosion

A  laboratory was seriously damaged when the rotor of an ultracentrifuge failed while in use. Flying metal fragments damaged walls, the ceiling and other equipment. The shock wave blew out the laboratory's windows and shook down shelves.

Description of the Accident

Milk samples were running in a Beckman L2-65B ultracentrifuge using a large aluminum rotor (a rotor is a large metal object that holds the individual sample tubes and is connected to the spin drive of the centrifuge). The rotor had been used for this procedure many times before. Approximately one hour into the operation, the rotor failed due to excessive mechanical stress caused by the "G" forces of the high rotation speed.

The subsequent explosion completely destroyed the centrifuge.The safety shielding in the unit did not contain all the metal fragments. The half-inch thick sliding steel door on top of the unit buckled allowing fragments, including the steel rotor top, to escape Fragments ruined a nearby refrigerator and an ultra-cold freezer in addition to making holes in the walls and ceiling. The unit itself was propelled sideways and damaged cabinets and shelving that contained over a hundred containers of chemicals .   Fortunately, sliding cabinet doors prevented the containers from falling to the floor and breaking. A shock wave from the accident shattered all four windows in the room. The shock wave also destroyed the control system for an incubator and shook an interior wall causing shelving on the wall to collapse. Fortunately the room was not occupied at the time and there were no personal injuries.

The cause of the accident is believed to be the use of a model of rotor that was not approved by Beckman for use in a model L2-65B ultracentrifuge.

Preventing Centrifuge Accidents

Rotors on high-speed centrifuge and ultracentrifuge units are subjects to powerful mechanical stress that can result in rotor failure. In addition, improper loading and balancing of rotors can cause the rotors to break loose while spinning. Everyone using this type of equipment needs to know the proper operating procedures for the specific unit being operated, including how to select, load, balance and clean the rotor. These procedures are explained in the unit's operating manual.

It is also necessary to "de-rate" some rotors (limiting the maximum speed at which the rotor is used to some level below the maximum speed listed for the rotor when new) based on the amount of use the rotor has received. This requires that operators maintain a comprehensive use log for each rotor. These procedures are explained in the operating manual.

Laboratory supervisors must see to it that operators of this type of equipment are properly trained in the selection, care and use of rotors. In the event a trained and experienced operator is not available to train new operators, contact the service representative for the unit and arrange an orientation program. Check the contact list below for details. If you are unable to reach the manufacturer, please contact EHS.

Special Warning for Older Equpment

Older equipment does not have all the safety features built into new units. They are more likely to experience rotor failures and they are more likely to cause injuries when they fail. It is critical that all safety and maintenance procedures specified by the manufacturer are followed. Based on the investigation of this incident, EH&S learned that Beckman L2 and L3 series ultracentrifuges have special operating procedures and restrictions to reduce the risk of damage and injuries. This includes an orange decal on the sliding door that specifies the rotor models that are safe to use in a particular unit.

If you have this type of unit and prefer to take it permanently out of service, please disconnect the units from the electric outlet then cut the power cord from the unit.

Beckman Instruments Urgent Corrective Action Notice, (Adobe Acrobat format) dated June 22, 1984, many years before this incident, describes two similar centrifuge accidents. The letter goes on to explain that operators of Beckman centrifuges must use only the specific types of rotors that are approved by Beckman for each specific model of centrifuge. The letter provides the complete list of approved rotors for all model L, L2, L3 and L4 centrifuges. Note: While this letter was sent to owners of Beckman centrifuges in 1984, the information is still appropriate for these models. It is very important that operators of these units follow these guidelines.

Centrifuge Safety Resources

The Howard Hughes Medical Institute has produced an excellent 10 minute videotape on centrifuge safety.  Tapes can be ordered free of charge from their website:  http://www.hhmi.org/research/labsafe/training/videos.html

Additional centrifuge safety information, including the eckman/Coulter Rotor Safety Guide and the Sorval Rotor Care Guide, (a large pdf file posted by Perdue University)  are  available at the AIHA Laboratory Health and Safety Committee, Laboratory Equipment page.

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       Fisher 16 Microfuge Explosion

A rotor on a Fisher Micro 16 microfuge exploded.   No one was hurt.  The outer shell of the centrifuge did not contain the explosion and fragments of the rotor sprayed all over the area.  The entire front of the centrifuge was blown off.  It passed from one bay in the lab to the adjacent bay, smashing bottles as it went.  The front narrowly missed hitting a technician's head.

Another technician who had her back turned to the centrifuge, felt fragments of the rotor spraying her back.

The centrifuge was purchased in October 1996.   Fisher takes this event very seriously and has issued a recall notice for Micro 16, Micro 14 and Micro 13 units.  The centrifuges involved are several years older and the serial number must begin with the letter M.

The manufacturer of the centrifuge, Denver Instruments stopped making these units years ago.  There have been several recalls of the centrifuge in the past, including one to ensure that the cover of the spin chamber clamps shut securely.  The centrifuge that blew had the recall repairs.

Rotors must be periodically inspected for wear and damage.  See recommendations in the incident described above.

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       Chemical Waste Explosions (top)

        Researcher Burned in Chemical Explosion   
        Due to Improper Disposal of Chemicals

Key Instruction Points:

1.  Segregate and dispose of hazardous waste properly
      through EHS

2.  Use appropriate personal protective equipment.

EHS was notified of a chemical spill in a laboratory at the ____ Building.  At that time, EHS was also told that a technician was sent to the Emergency Room because of skin, eye and respiratory irritation.  EHS responded and found yellow liquid splattered on the walls, ceiling and floor.  Many bottles of chemicals were placed in a red bag medical trash can, of which several were broken.   In addition, there were many more bottles on the countertop and floor. 

EHS was told that two technicians were cleaning out old chemicals from their lab.  They had put the bottles of chemicals  into the red bag waste bin, when it appeared that one of the bottles containing ferric chloride broke.   An acid mist was created, possibly by water or other broken bottles of chemicals also being present in the bin.    The technician stepped closer and peered into the waste bin when an explosion occurred.  The yellow liquid splashed all over him.

He immediately took off his lab coat and shirt and showered under the emergency shower and then went to the emergency room.  He suffered corneal abrasions and primary and secondary burns to his face.

The resulting damage cost in excess of $2,500.   Investigation revealed the following:  the lab had been inspected by EHS less than a year ago and was advised to dispose of any old or unwanted chemicals through EHS.   At no point was EHS ever informed that the lab needed to dispose of chemicals.

Over the summer, in a similar incident, EHS was anonymously alerted that another laboratory was performing a laboratory cleanout and was disposing of chemicals in their housekeeping trashcan.  EHS conducted an investigation and located the dumpster where the trash was disposed.  In it were benzene, hydrochloric acid,  hydrogen peroxide, mannite, pyroxilin and soduium hydrosulfite.  All of the illegally disposed chemicals were taken out of the dumpster by EHS and were properly labeled and stored in our waste facility.  Fortunately there were no serious repercussions.

What are the lessons from these two incidents?   First, all employees must be trained to do their jobs.  All lab personnel must be up to date in Lab Safety Training, which includes Chemical Waste Handling. Also, all hazardous waste must be disposed of by contacting EHS.  As stated in the Chemical Hygiene Plan, laboratories wishing to dispose of chemicals should schedule a chemical pickup through EHS.

Lab workers should wear personal protective equipment and should take care to ensure that incompatible wastes are not mixed.  And finally, all laboratory guidelines described in the Chemical Hygiene Plan should be followed to protect the health and safety of the housekeeping staff and co-workers.

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       Waste Solvent Explosion and Fire

Key Instruction Points:

1.  List all contents on hazardous waste labels.

2.  Do not mix incompatible chemicals.

At the University of X, in the hazardous waste facility, a 55 gallon drum containing 30 gallons of mixed organic solvents exploded, launching upward into the ceiling.  A significant fire ensured.  Luckily no one was hurt.

The mixed organic solvents in the drum had been consolidated from solvent waste containers from laboratories throughout the campus.  A similar consolidation process is used at many institutions.  Solvents are consolidated because there is a significant cost savings in disposing of one large drum compared to disposing of many small containers.  This incident demonstrates why it is so important for each lab to fully list the contents on the container's hazardous waste label.

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       Chemistry Explosions (top)

Lithium Aluminum Hydride/ Tetrahydrofuran Explosion  (top)

A researcher at X was seriously injured last December when reducing a substrate using lithium aluminum hydride (LAH) in tetrahydrofuran (THF). Within the last year, at least two other accidents involving procedures using LAH and THF have been documented. Due to the inherent hazards of LAH and THF, researchers must thoroughly plan out experimental protocols and incorporate safety measure to mitigate the hazards of this procedure. We have consulted with an outside expert in these issues, and he has made a number of important safety recommendations for this procedure.

Experimental Review

Figure 1 shows a typical equipment configuration for reducing a substrate with LiAlH₄ (LAH) dissolved in tetrahydrofuran (THF).

  Following a typical protocol, an experimenter would:

* heat and flush a 3-neck, glass flask with nitrogen to drive off all moisture.
* remove heat source and cool the flask, but continue to flush with nitrogen.
* add a stir bar, THF (freshly distilled), and LAH
* flush with nitrogen for the rest of the procedure surround the flask with an ice bath.
* turn on the stirrer.
* start water running through the closed loop of the condenser.
* start drop-wise addition of the substrate (which is dissolved in freshly distilled THF)

However, this 'typical' setup is not necessarily the best setup.

Experimental Recommendations

Listed below are several recommendations pertaining to this procedure:

 1. Use enough solvent to dissolve all LAH. Adding substrate to a slurry of undissolved LAH and solvent is almost as dangerous as adding it to dry LAH. The solubility of LAH in THF is 13g LAH/100g THF at 25oC, and in diethyl ether, 35g LAH/100g diethyl ether. Aldrich does not make solutions more concentrated than 1M (38g/liter). It is recommended to make solutions no more concentrated than 1M.

 2. Add LAH to THF rather than adding THF to LAH when preparing solutions. Dissolving LAH in THF is very exothermic! If THF is added to dry LAH, the LAH can easily overheat and decompose exothermically, especially on larger-scale reactions.

 3. Keep the ratio of LAH to substrate low. If the reaction goes awry, it's safer to have only a 2-fold excess LAH rather than a 10-fold excess to deal with.

 4. Ensure that the stopcock on the substrate dropping funnel works smoothly. If the stopcock sticks, too much substrate may be delivered, creating excess heat in the reaction flask.

 5. Ensure that the reaction flask is under a nitrogen blanket. Double check that the nitrogen inlet tube is securely fastened and all air is excluded from the reaction vessel.

 6. Prepare the substrate carefully to exclude any residual solvents that might react with LAH. This way, you won't have to use as much excess LAH.

 7. Ensure that the substrate/THF solution is free of peroxides. Any added THF should be freshly distilled.

 8. Use chilled silicone oil instead of ice and water as a cooling medium. This is now current industrial practice for large-scale reactions. If the flask breaks for any reason, LAH will not react with silicone like it does with water.

 9. Use an explosion shield when working with large-scale reactions. Lowering the fume hood sash and wearing protective eyewear is adequate with smaller scale reactions.

 10. Quench the reaction mixture, by addition of water or other quenching agents, using extreme caution. Add the quenching agents slowly!

If you have any questions, call your safety office.

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Explosive Decomposition of an Organic Azide

Key Instruction Points:

1.  Review risk assessment when scaling up reactions.

2.  Use engineering safeguards for containment and remote handling when using reactive materials.

Incident Description: A chemistry graduate student was isolating an organic azide (benzyltriethylammonium azide) as an intermediate in a process to synthesize a complex organic molecule to be used in a cancer treatment.   (She was trying to prepare a 5-deoxy-5-azido nucleoside by azide displacement of the 5-tosyloxy derivative).  Several days earlier she had isolated a small amount of this organic azide intermediate by using a rotary evaporator to drive of the reaction solvent.  Approximately 0.5 grams of material were initially isolated and used to run analytical tests to demonstrate the purity of the isolated intermediate.  Now that she had demonstrated that the initial steps in her synthesis process were successful she scaled up the process 20 fold in order to isolate enough organic azide to continue her synthesis.

At approximately 9:00 on a Sunday night, while working in the lab with two other graduate students, she completed the isolation of approximately 7-8 grams of organic azide in the rotary evaporator.  The rotary evaporator was set upon the open bench in the middle of the laboratory.

After isolating the organic azide from a 1:1 solution of acetone and methylene chloride in the Buchi rotary evaporator, she lifted the 250 ml round bottom flask containing the organic azide from a water bath,  with the handle provided for this purpose, using her left hand, while her right reached out for the flask.

The flask exploded in her hand, shattering all of the glass associated with the rotary evaporator and glass containers close by on the lab bench.   Parts of the condenser were found in a hallway approximately 15 feet away. 

Her recollection of the incident and the nature of her injuries, indicate that she did not have the opportunity to break the vacuum on the system or stop the rotation of the flask.  It is believed that the raising of the flask alone from the warm water bath initiated the decomposition of the shock sensitive organic azide, perhaps by creating a movement in a contaminated ground glass joint.  However, the graduate student does not feel that solvent "bumping" occurred in this case.   This could have caused the azide compound to contaminate the glass joints.

Injuries and property damage caused by the incident: The glass fragments from the exploding flask severely lacerated the graduate student's right hand and cut her cheek and forehead.  The force of the explosion blew her to the floor where she lay stunned and bleeding.  The safety glasses she was wearing protected her eyes from glass fragments; otherwise she may have been blinded.  The two students with her immediately came to her aid and called an ambulance that transported her to the hospital five minutes away.  That night a four-hour surgical operation removed the glass from her face and hand and subsequent surgery restored most, but not all, of the functionality of her hand.  She lost the ability to move her thumb.   She also underwent multiple plastic surgery operations to improved her appearance.

Resources spent responding to the incident:  The local fire department responded, and because the incident involved an explosion, the State Fire Marshall's office was also called in.  Three University EHS employees took part in the six hour investigation with the three state inspectors and two representatives of the local fire department.  The building was closed until the investigation was complete.   Upon completion of the State Fire Marshall's investigation, EHS employees cleaned up the spilled materials and blood.

Cause of the incident: The explosion was caused by the rapid decomposition of the organic azide which it is believed had worked its way into the ground glass joints between the product flask and the glass column on the rotary evaporator. However, after interviewing the graduate student it was apparent that several factors lead up to the incident including:

1.       The graduate student had underestimated the risks associated with the material she was isolating.  Although she was aware generally of the decomposition potential of azides she did not know just how shock sensitive the organic azide she was isolating was – even though this information was available in the literature.

2.       Due to the underestimation of risk, she isolated the azide on open bench with out adequate containment such as a laboratory hood and shielding, personal protective equipment, or procedures.

3.       She did not reassess the risk when scaling up her reaction.   If she had, she would have realized that the material being handled had significant explosive power and due to its inherent instability required substantial shielding and remote handling.

 Recommendations:   To prevent future accidents of this type the following steps were taken:

1.       The types of "high-risk" reactions that were being conducted in the Chemistry Department were identified.  Based on the type of reaction and the scale (quantity of material), the appropriate safety precautions (both engineering controls and personal protective equipment) were identified and placed in a matrix.  This safety precaution matrix table was distributed throughout the Chemistry Department and required to be followed.

2.       A formal peer safety review process was established that required the following steps be completed before graduate students were allowed to beginning research: (1) a comprehensive literature review must be conducted (safety and chemistry); (2) a protocol safety review form summarizing the hazards and precautions to be taken is completed; and (3) The planned research, information uncovered in the literature review, and safety review form, is reviewed with a peer. 

3.       A shared use facility was established in which high-risk reactions could be performed and special procedures for performing these reactions established.

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       Stirred Reaction Flask Explosion

Key Instruction Points:

1.  Don't leave reaction unattended.

2.  Use proper PPE.

3.  Control sources of contamination.

4.  Set chemical hood sash to lowest height possible.

Background- At 10:11:44am, Wednesday, 9 February xxxx, the Fire Department received an alarm from the Chemistry Building, and responded with fire and EMS personnel.  County Sheriff officers also responded.  At about 10:35am, EH&S personnel arrived at the incident site.

 At about 10:10am, an explosion occurred within the Chemistry Laboratory.  A Ph.D. research student, performing an experiment inside a fumehood, was injured by flying glass shards, which were generated from an explosion that occurred in a reaction flask (see photo below).  Although the fumehood sash was partially down (about half way), the researcher received injuries mostly to the right side of his face (see photo below) and to his left hand and arm.  No injuries were associated with the eyes since the researcher was wearing safety glasses with side shields. 

The researcher was de-conned in the laboratory emergency shower and received first aid from laboratory personnel, who are also safety representatives for the laboratory.  After the first aid treatment, the researcher was escorted from the building to meet the arriving Fire Department EMS personnel.  The EMS personnel then transported the researcher to a near by building for further deconning in a hot water shower.  Afterwards, the researcher received additional first aid before being transported to the Hospital ER for treatment and observation.  Late in the afternoon, the researcher was release from the ER.  On the following Monday, the researcher returned to his laboratory at the Chemistry Building.

 Description of Experimental Procedure- The experiment being performed was a modification of the Simmons-Smith cyclopropanation procedure for the synthesis of species for reacting with olefins.  Very simply, in a stirred reaction vessel under a dry argon atmosphere containing an ultra-low water and oxygen solvent (250 mL dichloromethane; CAS# 75-09-2) cooled to -10^oC by dry ice in acetone, two reactants (diethyl zinc; CAS# 557-20-0 and methylene iodide; CAS# 75-11-6) are sequentially introduced via a fill funnel under dry argon pressure.  Photos of the experimental apparatus and equipment are shown in the Incident Investigation section below.   In between fillings, the funnel is rinsed with the solvent fed from a one-use, sterile plastic syringe.  First, diethyl zinc (13 mL) is added from its container with a double-ended needle to the solvent at about 2.5 mL/min.  Next, methylene iodide (22 mL) is added with a glass syringe to the solvent mixture at about 1 mL/min.  After the final addition, the solvent mixture is allowed to continue to stir for 20 min producing chemical species for reacting with olefins.  As the reaction goes to completion, the solvent mixture turns milky with the formation of a fine precipitate, which is normal.

Description of Incident- The experiment was performed as stated in the SOP, which was recorded in the researcher's lab notebook, up to and including the addition of the methylene iodide to the dichloromethane and diethyl zinc mixture under an inert argon atmosphere.  After the methylene iodide (22 mL) was added at a rate of about 1 mL per min over a time period of about 25 min, the researcher noted that the experiment was proceeding normally.  At this point, he left the experiment in the fumehood for the reaction to continue for about 20 min.  However, he decided to return after about 10 min to check on the experiment.  Upon returning, he noted the stir bar was not rotating due to the formation of an unusual amount of precipitate in the bottom of the reaction flask.   The reactant mixture was clear, but with no liquid phase separation.  The appearance of the reactant mixture was unusual; normally the mixture would appear milky white due to the suspension of a fine precipitate.  Although the stir bar was not rotating, the researcher did not perceive the risk of an explosion.  So he immediately proceeded to restart the stir bar.  During this process, when he had the reaction flask in his left hand, the contents of the flask detonated.  From the flying glass shards, the researcher sustained serious injuries to the left hand, right neck, and right side of the face (see above photo) from flying glass shards.

 NOTE: Terms such as explosion and detonation will be used through out this report with the realization that a very rapid release of energy may have occurred without an actual detonation.   Regardless, the energy release and the subsequent pressures were so rapid and great that the neck of the flask could not vent the pressure buildup.  After the incident, there was no evidence of fire/smoke or other combustion products. 

Incident Investigation - After an interview with the injured researcher, a reenactment of the experiment was performed substituting water for the chemicals: dichloromethane, diethyl zinc, and methylene iodide.  The experimental setup and equipment are shown in the photos below (clockwise: experimental apparatus, diethyl zinc container, and rinse syringe).

The experimental apparatus, under a positive-pressure argon atmosphere, is continuously fed from an argon cylinder through a drying column.  Setting atop the round bottom flask, which is the reaction vessel, is a septum-fitted funnel for feeding the reactants.  The reactants are fed via double-ended needles (diethyl zinc), plastic syringes (dichloromethane), or glass syringes (methylene iodide) into the funnel, and then fed into the flask through a stopcock.  The only difference in the mock setup and the experimental setup was the use of an open bath rather than a half-sphere Dewar.  This difference was not judged to be a factor in the incident.

Primary physical hazards associated with the chemicals components were the flammability of dichloromethane (LFL 13%, UFO 23%), methylene iodide and diethyl zinc incompatibilities (see http://xxxx.edu/~msds/), and the pyrophoricity, water reactivity, and explosive heat-sensitivity of diethyl zinc.  Of particular concern are the incompatibilities of the two reactants with other chemicals such as alkenes, oxidizers, copper-zinc alloys, potassium-sodium alloys, and potassium.  For example, alkenes in the presence of the reactant mixture could result in an explosive reaction and in the presence of potassium form a shock-sensitive mixture.  During the reenactment of the experiment, several possible causes for the incident were identified and are addressed in the following table.

 

Hazard Assessment Table         

Explored Cause	Likely Effect
Introduction of water via the glassware and reusable syringes	Since there is a SOP for washing glassware and reusable syringes, it is not likely.  If it did happen, there might be no sign to small amounts of visible emissions in the flask; no signs were noted.
Injection of water with the dichloromethane or methylene iodide	The dichloromethane is dried in the purification process, which is under a dry nitrogen atmosphere; not likely contaminated.  The methylene iodide is transferred from a glass bottle, which is used by several researchers.  Probably some water could be introduced resulting in no sign to visible emissions in the flask; no signs were noted.
Injection of oxygen with the dichloromethane or methylene iodide	Oxygen is removed from the dichloromethane in a purification process, which is under a dry nitrogen atmosphere; not likely contaminated.  The methylene iodide is transferred from a glass bottle, used by several researchers.  Probably some oxygen could be introduced resulting in no sign to visible emissions in the flask; no signs were noted.
Loss of argon atmosphere	The argon cylinder was still under pressure, and argon was still flowing after the incident.
Increase temperature of the reactant mixture	The only heat source is the heat of reaction.  The magnetic stirrer did not have a heating element.  The final reactant was added over a 25-min time period to prevent large temperature increases.  In addition, the reactant mixture was cooled in a Dewar to -10oC by a dry ice/acetone solution.  Nevertheless, if a large temperature increase had occurred, detonation could result.
Introduction of a fourth chemical component via the glassware, syringes, or contamination in other components	Because of the very strict cleaning, rinsing, and drying procedure used on the glassware and reusable syringes, it unlikely that amounts of contamination could be introduced that could result in an explosion.  Evaluation of the solvent and diethyl zinc sources indicates it is unlikely that these are sources of contamination.  However, the methylene iodide (stabilized with copper or silver mesh) is purchased, stored, and used out of a glass bottle by many different researchers.  It is judged to be a possible source of contamination.

Conclusion - A definitive conclusion could not be made as to the specific cause of the detonation of the reactant mixture.  However, based on the above hazard assessment, two likely causes of the explosion detonation were a very rapid increase in temperature of the reactant mixture and the introduction of a fourth chemical, as a contaminant, into the reactant mixture.  The introduction of a third reactant could possible explain the formation of unusual amounts of precipitate, which settled to the bottom of the reaction vessel stopping the magnetic stirrer from rotating.  The stopping of the magnetic stirrer was judged to be the abnormal occurrence that preceded the explosion and perhaps was the causality for the explosion.

The use of safety glasses probably saved the researcher from serious eye injures.  Nevertheless, additional protection to the face and body would have reduced the number and severity of the injuries received.

Recommendations

1)      Do not leave this experiment unattended; ensure that the reactant solution is continuously stirred.

2)      Use additional personal protective equipment such as full faceshield and blast shield when conducting experiments with highly reactive components.

3)      Assess the operation of the dichloromethane purification unit to ensure high purity.

4)      Review the glassware cleaning procedure to ensure no contaminates are present.

5)      Discontinue the use of sterile syringes for introducing chemicals into the experimental apparatus.  The term "sterile" is no indication of "chemical contamination levels."

6)      Assess the use of the methylene iodide to reduce the likelihood of contamination and implement the following controls:

a) Date the container as to when received.

b) Date the container as to when opened.

c) Implement procedures to ensure minimum
                container open  time.

    d) Set criteria for methylene iodide use, considering
         such parameters as color and age.

7)      Always set the fumehood sash at the lowest usable height.

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       Chemical Solution Preparation
       Explosion

Key Instruction Points:

1.  Review hazards of chemical combinations prior to start.

2.  Use proper PPE for the task.

3.  Lower hood sash to the lowest possible height.

Description of Incident:  A teaching assistant was preparing a 30 L solution 0.04 M KMnO4 in 0.5 M H2SO4 for use in  chemistry instructional laboratories.  She was working by herself.  This is a laboratory where all solutions for use in the general chemistry laboratories are prepared.  Her supervisor was working in his office which is adjacent to the preparation lab and connected by a doorway. A chemistry class was underway in a lab across the hallway.  This teaching assistant had a BS and MS in chemistry and working at the university for two years.  Her responsibilities included preparing solutions for the chemistry program since the start of her employment.

She indicated she was following a procedure she has followed without incident in previous semesters (estimated 10-12 previous preparations). She indicated the procedure was contained in a notebook containing standard procedures for preparing all of the reagents used in the two classes.  On the day of solution preparation, was not referring directly to the written procedure since she had used it sufficiently in the past that she did not need to refer to it.  The quantity prepared is typically 10-20 L; this was the first instance she could recall in which 30L was to be prepared.

The notebook containing the written procedure has not been located.

To make 30 L of the solution, 833 ml of 18 M sulfuric acid was needed.   This was measured out, transferred to a 1 L beaker which was placed on a stir plate in the hood.  The volume of acid was obtained from two sources: the last 200-300 mL of sulfuric acid remaining in a bottle that had already been opened and the balance from a new unopened bottle.  Both sulfuric acid bottles were 2.5 L in size.  A 40 L Nalgene tank was filled with approximately 22 L of deionized water and placed in the hood.  Solid reagent grade potassium permanganate (189.648 grams) from a bottle dated 9/10/96 was weighed out into a clean beaker on a top loading balance on the lab desk.  This was slowly added to the acid on the stir plate (estimated over a period of 30 seconds).  The solution heated quickly and began to boil in 1-2 minutes.   Because it was spattering, the solution was picked up with gloved hands so that it could be transferred into the DI water and diluted before any more was lost.  Before any of the solution could be transferred to the DI container, the beaker broke, spraying acid and permanganate everywhere.

The teaching assistant sustained chemical burns to the upper body, any uncovered areas.  She was wearing safety glasses, not goggles, gloves, and a short sleeved shirt. 

 The supervisor later indicated that the calculated amounts described above for preparation of the 30 L solution were correct.  If the material had not broken, the contents would have been added to the 22 L DI container over the course of a few minutes, the container would have been filled 30 L with DI, stirred, and then dispensed into three 2 liter containers.  The remaining solution would be placed into a 20 L carboy for subsequent refills of the 2 liter containers for lab work later in the week.

Probable Cause of the Incident:  Several pertinent references in the literature regarding the mixtures of potassium permanganate and sulfuric acid indicate caution.  Bretherick's Handbook of Reactive Chemical Hazards states:

"Addition of concentrated sulfuric acid to the slightly damp permanganate caused an explosion.  This was attributed to formation of permanganic acid, dehydration to dimanganese heptoxide and explosion of the latter, caused by heat liberated from interaction of sulfuric acid and moisture.   A similar incident was reported previously, when a solution of potassium permanganate in sulfuric acid, prepared as a cleaning agent, exploded violently.

Manganese heptoxide is formed as a dense green-brown oil by reaction between potassium permanganate and concentrated sulfuric acid.  Kleinberg, Argersinger and Griswold, Inorganic Chemistry pg 534 states that the reaction between potassium permanganate and sulfuric acid is:

                   2 KMnO₄ +  H₂SO₄ = Mn₂O₇ + K₂SO₄ + H₂O

AManganese heptoxide begins to lose oxygen at 0^B and decomposes with explosive violence when warmed.

Durrant and Durrant, Introduction to Advanced Inorganic Chemistry pg 1014 states ...

A Manganese heptoxide, exists as dark green, explosive crystals.  It is made by adding powdered potassium permanganate to cooled concentrated sulfuric acid.  A dark green solution is formed which is explosive.  Manganese heptoxide is stable at -5^B, but it begins to give off oxygen at 0^B, and at about 10^B it explodes yielding manganese dioxide.

The most probable cause of this incident was the explosion of manganese heptoxide formed by the reaction of potassium permanganate and concentrated sulfuric acid.

Corrective Action:  

1.  An alternate procedure for preparing the solution will be developed.  Procedures for preparation of all instructional lab reagents will be reviewed.

2.  Use of protective equipment will be re-emphasized.  The teaching assistant wore glasses and gloves, but no lab coat and faceshield, sustaining burns to the face, arms, and upper torso.

3.   Re-emphasize the availability and requirement to review health and safety information resources provided to supervisors and employees.  This information (ACS booklet) indicates caution in mixing of sulfuric acid and potassium permanganate.

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Phenyl Azide Compound Erupts During a Vacuum Distillation

A Post-Doc was purifying a fluorinated phenyl azide compound via vacuum distillation over a heating/stirring mantle. The resulting explosion caused the ceramic mantle fragments to cut and embed themselves in the experimenter's face. Fortunately, she was not seriously hurt and she was wearing her safety glasses.

What can be done to prevent this from occurring again?

There is no substitute for pre-planning your experiment and to discuss various techniques with your supervisor. Heating mantles are not good choices for vacuum distillation if the materials used are heat sensitive or unstable (such as most azides). This is because it is difficult to regulate precise temperature control with a heating mantle. A better choice would have been to use a hot oil bath or use chromatographic techniques to isolate the substances.

While the Post-Doc was wearing eye protection, the fume hood sash was in the wide-open position. This allowed the fragments to strike her face. If the sash must be open during the experiment, a portable blast shield should be used. If you know that the materials are unstable, safety glasses with a full face shield would be appropriate choices for PPE.

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     Cryogens (top)

       Glass Flask Ruptures, Possible       
       Overpressurization by Liquid Nitrogen

Key Instruction Points:

1.  Consider shielding for operations involving vacuum or pressurization.

2.  Be aware of the potential for pressurization when working with cryogenic liquids.

A 250 ml glass flask became overpressurized and burst, spraying two laboratory workers with shards of glass.  Approximately 10 grams of styrene and a minute quantity of a drying agent were immersed in liquid nitrogen to keep the contents frozen.  The laboratory workers then attached the flask to a vacuum pump to evacuate the flask, without success.  Thinking the flask might have developed a crack, the laboratory worker removed the flask from the vacuum line and was defrosting it under warm water in the sink, holding it and examining it, when the flask ruptured.

The best guess as to the cause of the rupture is that a small leak, perhaps a pinhole in the flask, developed wile it was being frozen and that some liquid nitrogen entered the flask.  When the flask was warmed, the liquid nitrogen vaporized (expansion ration 696:1), overpressurizing the flask and leading to the explosion.

The laboratory worker holding the flask suffered from several lacerations to the face, hands, chest and abdomen.  The other worker, who was standing across the room, received lacerations to the abdomen.  The worker holding the flask noted shards of glass embedded in his prescription safety glasses.

The procedure was re-written such that under the same conditions, the stopcock will be unscrewed and the flask set in a catch-bucket in the hood to allow the contents to warm up and vaporize, if volatile.

Appropriate eye protection helped to avoid a potentially serious eye injury.  Consider shielding for operations involving vacuum or pressurization.   Be aware of the potential for pressurization when working with liquid nitrogen.

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       Researcher Blinded in One Eye from
       Cryotube Explosion

Key Instruction Points:

1.  Consider shielding for operations involving vacuum or
      pressurization.

2.  Be aware of the potential for pressurization when
      working with cryogenic liquids.

3.  Use appropriate personal protective equipment.

A University of X investigator was blinded in one eye when a cryotube exploded while being thawed.  The probable cause was the rapid expansion of liquid nitrogen that had entered the tube through a small crack during storage.   Suitable personal protective equipment for thawing cryotubes and handling cryogenic liquids consists of a face shield, heavy gloves, a buttoned lab coat and pants or a long skirt.  Cryotubes should be kept in a heavy, walled container or behind a safety shield while warming.

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       Investigator Exposed to Infectious
       Material in Cryotube Explosion

Key Instruction Points:

1.  Be aware of the potential for pressurization when working with cryogenic liquids.

A researcher at a university reported that a vial of potentially infectious materials "exploded" when she removed it from liquid nitrogen.

As you may have guessed, the "explosion" occurred when the liquid N2 that has leaked into a vial expands when removed from the cold.  This used to be a fairly common problem with heat-sealed glass ampules, because it was difficult to obtain perfectly fused glass with no microscopic holes.  This problem was largely resolved with laboratories began using plastic cryovials with a silicone seal.  Nunc* makes a sleeve called CryoFlex that slips over the vial and then is heat-sealed to keep the liquid out.  However, even with this type of product an explosion infrequently occurs.

There are several ways to prevent this from happening:

1.  Cryogenic storage vials are designed for VAPOR PHASE STORAGE in liquid nitrogen freezers.  This means that they are designed to sit in the cloud of extremely cold nitrogen gas that sits just above a small reservoir of liquid nitrogen in the bottom of the freezer.  Leakage of liquid nitrogen into the vial occurs with the freezer is overfilled and the vials are immersed in liquid nitrogen.   This problem can be avoided by not overfilling the freezers with liquid nitrogen.

2.  Visually check each cryovial prior to filling to ensure there are no defects around the rim.  Cryovials should never be re-used.

3.  When removing samples, pause for a moment in the neck of the dewar before bringing them into the room atmosphere - if one is going to pop, it will usually do so early in the warm-up process.

The importance of gloves and face shield can not be overemphasized.   Tubes stored in liquid phase dewars, where the ampules are in canes is especially hazardous.  Since nitrogen freezers tend to be located separate from the labs, full face shields and gloves should be available near the nitrogen freezers so no one is tempted to pull a vial without protection because they forgot to bring a shield with them.

Information about Nunc products is at:  http://nunc.nalgenunc.com/products/catalog/handling/index.html

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     Incompatible Chemicals (top)

        Oxidizer Solvent Explosion

A corrosive storage cabinet under a chemcial hood in a University undergraduate laboratory was the site of an early morning explosion.   Luckily, no one was standing in front of the hood when the explosion occured.   We believe the explosion resulted from nitric acid (an oxidizer) and an organic solvent being mixed in a closed container.

Niric acid reacts violently with most organics resulting in heat, gas or fire. In a sealed container, the pressure would increase due to the expanding gas.   Never mix nitric acid with organic materials (especially in a sealed container) unless the reaction has been thouroughtly investigated.  Do not store nitric acid in the same cabinet as organic solvents or organic acids such as acetic acid.

Incidents such as this have occurred on this campus and at other universities in the past, some with more severe consequences.  Help make your campus safer by following proper storage guidelines for chemicals.

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Glass Waste Bottle Ruptures, Possible Reaction of Incompatible Chemical Wastes

Key Instruction Points:

1.  Chemical containers should be triple
      rinsed and dry before being used for
        waste accumulation.

2.  Wear safety glasses while in the
      laboratory, even while performing
      non-laboratory work.

A graduate student sitting at a lab computer was surprised by a chemical waste bottle which burst and sprayed nitric acid and shards of glass all over the lab.

Approximately 2L of nitric acid waste had been accumulated in a chemical waste bottle which originally contained methanol. Over the course of 12-16 hours, it is likely that some residual methanol reacted with the nitric acid waste and created enough carbon dioxide to overpressurize the container. Two other waste containers in the hood were severly damaged and several others were cracked or leaking.

Fortunately, the laboratory worker was not injured.

Chemical containers should be triple rinsed and dry before being used for waste accumulation. Safety glasses should always be worn while in the laboratory, even while performing non-laboratory work.

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Mixing Diaminopropane and Potassium Hydride

A Post-Doctoral Fellow was adding 100ml of Diaminopropane to 150g of Potassium Hydride in a 2L, 3-necked, round-bottomed flask while under Nitrogen.  As she was adding the Diaminopropane, the reaction began to foam and fill the flask.  As she was replacing the stoppers, the mixture built pressure and then splashed her right arm, left wrist, face, and neck.  

What can be done to prevent this from occurring again?

Before setting up an experiment, thoroughly investigate the properties of materials involved. If you are unsure, ASK!  Potassium Hydride is an extremely reactive species.  For this particular reaction, 150g of hydride could generate nearly 60L of hydrogen gas at STP! 

Here are some general recommendations:

1) This was a large scale reaction.  The Post-Doc, who had never done this reaction, should have started out with very small quantities and then scaled-up (by no more than a factor of 5 each time).

2) Rather than adding the Diaminopropane to the hydride, add the hydride to the amine.  By slowly adding the hydride, you can control the reaction and the subsequent foaming (resulting from the hydrogen gas).  It would also be a good idea to have a cooling bath on a lab jack underneath the flask in order to slow the reaction down...just in case.

3) When working in the fume hood, keep the sash as far down as possible at all times. If you have to lift the sash to make an adjustment, use a safety shield (as appropriate) and/or use a face shield (in addition to your safety glasses).

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Two Explosions Involving Aqua Regia

Key Learning Points

1. Use a reagent that is milder than aqua regia for cleaning glassware if it will suffice.

2.  Do not take aqua regia out of the fume hood in which it was prepared, and do not store it there either; make only what you need and destroy the residue.  Aqua regia can be destroyed by cautious and careful dilution with water - talk to your supervisor or your safety office for a detailed procedure. If necessary, the solution can then be neutralized and disposed of in the approved manner.

3. Never put aqua regia in a closed container or near flammables.

There have been explosions involving aqua regia ( a mixture of hydrochloric acid and nitric acid) reported at two universities. Both of the incidents took place in chemistry laboratories.

In the first incident, a graduate student was using aqua regia for the cleaning of NMR tubes. When he was finished, he placed the residues (about 50-60 ml) in a 4 litre waste bottle, capped it tightly and placed it in a flammable storage cabinet. Approximately one hour after the bottle was placed in the cabinet, it burst, breaking an adjacent bottle of pyridine. Luckily, the pyridine did not ignite and other nearby bottles containing flammable solvents did not become involved. The pyridine leaked onto the floor, where it dissolved floor tiles and created a lingering bad smell.

The second incident occurred in a fume hood in a synthetic chemistry laboratory.   A tightly closed waste bottle containing used aqua regia exploded, most probably due to  pressure buildup inside the bottle.

Since the sash was not completely closed the broken waste bottle was not contained. Broken glass as well as some liquid acid waste were thrown out of the hood.  Since nobody was near the hood at that moment, there were no injuries.   Moreover, a nearby bottle of mercury nitrate waste was also broken as well as the secondary container, so that a small spill (less than 1 liter) of liquid acid and solid mercury nitrate occurred inside the hood.

What is aqua regia?

Aqua regia has been used by chemists for centuries, especially as a medium for dissolving noble metals but also for other purposes. It is a mixture of concentrated hydrochloric and nitric acid which forms a powerful oxidizing medium. Mixing an oxidizer with organic materials may result in a highly exothermic reaction.  Even without other materials present, a chemical reaction occurs slowly and brown fumes of NO₂ can be observed (in freshman chemistry terms, nitric acid is reduced and hydrochloric acid is oxidized). The activity as a dissolving agent decreases slowly and so, by definition, the solution is unstable - it should be used "freshly prepared".

Rules for using aqua regia

Aqua regia is often used as a substitute for chromic sulfuric acid cleaning solutions.   However, aqua regia is also corrosive and strongly oxidizing.  It  is essential for some purposes but should not be used for routine cleaning of glassware.  If a milder reagent will suffice avoid using aqua regia.  Alternatives include ultrasonic baths, alconox or similar detergents, Pierce RBS-35 (available from VWR) or similar detergents or biodegradable surfactants. 

Be aware that sufficient pressure can build up in a  short amount of  time to burst the container,  even from a very small volume of aqua regia.

If it is decided that aqua regia is needed, wear protective clothing (goggles, gloves, coat) and work in a clean well-ventilated fume hood. Keep the sash down when reactions are in progress. Never take aqua regia out of the hood.

Prepare it, use it, and destroy any excess in the hood in which it was prepared.

Only prepare the amount of aqua regia you need for immediate use. Never store it and never put it in a closed vessel, since evolved gases will cause a pressure build-up and possible explosion.

Aqua regia is a strong oxidizer. It is incompatible with organic solvents, flammables and any reducing agents.

Lack of Venting Explosions (top)

Alert: Formic Acid Explosion and Explosive Laboratory Chemicals  The Australian University, Human Resources Occupational Health and Safety, December 1997

Refrigerator/Freezer Explosions (top)

Lab Freezer Explodes

Key Instruction Points:

1.  Flammable liquids must only be stored in refrigerators which have no internal ignition sources.

 Incident Description:  Many small tubes of petroleum ether were stored in an ordinary domestic freezer.  The tubes were not sealed well and over time the petroleum ether evaporated in sufficient quantity that the concentration exceeded the low explosive limit, about 1.0%.  A spark from an internal component caused the freezer to detonate.  (Photo)

 Injuries and property damage:  There were no personal injuries as the explosion took place at night.  There was $11,000 damage to the room and $25,000 damage to equipment in 1982 dollars.  This would be well over $250,000 in 2001 dollars.  Along with the freezer, one liquid scintillation was destroyed and another was seriously damaged.

 Primary cause of the incident:  Petroleum ether, a very flammable liquid* was stored in an ordinary domestic freezer which has components  (e.g., thermostat, light switch) which generates sparks.  This apparently caused the vapor of the liquid to detonate. 

*With a flash point as low as -56 °F, petroleum ether is classified as a Class 1A flammable with an NFPA 704 fire hazard rating of 4.

 Recommended Corrective Action:

1) All materials with a flashpoint below 100 °F may only be stored in a UL approved flammable materials storage refrigerator or freezer.  These units do not have any internal ignition sources.

2)      All ordinary domestic refrigerators and freezers must be labeled with the phrase "No materials with a flashpoint below 100 °F may be stored in this refrigerator/freezer."

Lab supervisors must vigorously enforce both of the above items.

Semiconductor Experiment Explosions (top)

       Failure to Manually Purge Hazardous
       Gases

Key Instruction Points:

1.  Don't rely on procedures - insist on engineerging
     controls.

2.  Use engineering controls to protect against unforseen
      hazards.

An experienced physical scientist (Ph.D. 15-20 years) at  an industrial reserach lab used hydrogen and phosphine gas, along with other materials, in a metal organic chemical vapor deposition system. This was a slightly modified commercial system that operated at atmospheric pressure. The reactor was contained in a secondary enclosure with exhaust ventilation and toxic and flammable gas detection equipment linked to automatic gas shutoff valves. The equipment operating procedure involved a manual inert gas purge prior to flow of hazardous gases. When considering a modification of the system to make the purge process automatic, the manual procedure was thought to be acceptable since the only one who operated the system was the physicist who bought and built the equipment and his coworker who was also experienced and trained. The addition of the automated purge feature was considered an unnecessary hardship. Three months after startup an overpressurization of the reactor occurred, cracking the glassware and leaking the gas into the secondary containment. The gas monitor detected the leak and caused automatic shutdown of gas flow. No gas escaped secondary containment. The physicist indicated that he had forgotten the purge step of the process.

Corrective Action - The physicist modified the equipment to include an automatic inert gas purge. This involved very little time and expense. This incident is consistent with other mishaps in which highly intelligent, experienced, and well trained personnel miss a critical step in the process. The need for engineering controls for high hazard processes was emphasized in employee training and hazard reviews.