Omnitrans

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FAQ Sheet

Frequently Asked Questions
About Gas Odor from Omnitrans
Compressed Natural Gas Fueling Station

Information Sources:
OSHA
AQMD
James F. Collines, PhD, DABT, staff toxicologist for California EPA
Airgas MSDS: Methyl Mercaptan
Matheson Tri-Gas MSDS: Methyl Mercaptan

What is the odor coming from the Omnitrans facility?
Is the methyl mercaptan odor harmful?
How much methyl mecaptan are we being exposed to?
Explain ppm (parts per million) in everyday terms?
Will the odors make me sick?
What about long term exposure risks?
Why is Omnitrans using this new fuel technology instead of traditional diesel?
Why do gas leaks occur?
What is Omnitrans doing to reduce chances of leaks?
Why can't Omnitrans shut down or relocate the CNG station?
What more can Omnitrans do to address our concerns?

What is the odor coming from the Omnitrans  facility?

The odor, which occasionally escapes from our compressed natural gas fueling station, comes from the methyl mercaptan which is added to the normally odorless, colorless natural gas. This compound is added to natural gas by the gas company as a safety measure. The human nose can detect this smell at very low levels, making it a safe way to detect the presence of natural gas in the event of a leak.  It is the same gas used to power home appliances like water heaters, furnaces, clothes dryers, ovens and ranges.

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Is the methyl mercaptan odor harmful?

Exposure to low levels of methyl mercaptan poses no serious health risk, according to the Occupational Safety and Health Administration (OSHA). OSHA sets the ceiling for permissible exposure levels for methyl mercaptan at 10 ppm (parts per million) per exposure.  The allowable level for repeated exposures such as a worker might experience, averaged over an eight-hour workday, is set at .5 ppm.   Exposure amounts from the Omnitrans station are well below these levels. The problem is that the human nose can detect methyl mercaptan at concentrations as low as 0.002 ppm.

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How much methyl mercaptan are we being exposed to?

The Southern California Gas Company natural gas lines which feed into the Omnitrans CNG station have been tested by AQMD and show that the odorant level in the gas is 2.7 ppm (parts per million).  When the odor is released into the atmosphere it will dissipate to even lower concentration levels.

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Explain ppm (parts per million) in everyday terms?

One part per million is equal to 1 drop (think eyedropper) in 14 gallons.

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Will the odors make me sick?

While there are no long term health effects associated with low level exposure, humans do react to the pungent smell in a variety of ways.  It does smell bad, like rotten cabbage.  We naturally turn up our nose and want to get away from bad smells. According to the California Environmental Protection Agency, some sensitive individuals may experience headaches and nausea when confronted by odorants such as methyl mercaptan. 

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What about long term exposure risks?

While acute and chronic exposure to very high concentration levels of Methyl Mercaptan can be harmful to respiratory and nervous systems and be an irritation to skin and eyes, the low level exposures generated by the Omnitrans CNG station are below harmful amounts.  Additionally, methyl mercaptan is not considered to be nor suspected to be a cancer-causing agent and is not known to have any effect on the human reproductive system, even in higher level exposures.  Further, it is not known to cause sensitization in humans upon repeated or prolonged contact.

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Why is Omnitrans using this new fuel technology instead of traditional diesel?

Omnitrans still does have and use diesel-powered buses, but since 1997 has purchased a total of 75 buses powered by compressed natural gas (CNG).  (27 more are due in Feb/Mar.) The San Bernardino CNG station became operational in 1998.  The decision to switch to CNG was an effort to help improve air quality in the region. CNG buses emit fewer smog-forming emissions than diesel buses.  Recently, the South Coast Air Quality Management District (AQMD) has passed a rule for transit systems like Omnitrans which requires all new transit buses purchased after 7/1/00 be powered by natural gas.

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Why do gas leaks occur?

The CNG station is a mechanical system which by its nature will at times emit small releases of gas. Occasionally packing and or seals in the compressors may weaken due to normal wear and tear and allow gas to escape through a vent pipe. Gas emissions also occur as a safety release measure when too much pressure builds up in the lines. 

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What is Omnitrans doing to reduce chances of leaks?

Recent work on the station to minimize odor problems includes replacing plugs, heaters, catalytic elements, oxygen sensors, exhaust gaskets, compressor engine exhaust catalysts and flex pipes.  We have welded catalytic housing cracks, cleaned the station, installed carbon filters, replaced methyl mercaptan bottles and installed isolation valves. Since December 1, 2000 the Omnitrans Maintenance Department conducts round-the-clock inspections of the station.  We have also doubled the number of inspection days provided by NGS, a contractor which provides routine and preventative station maintenance.

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Why can't Omnitrans shut down or relocate the CNG station?

Omnitrans cannot shutdown the station without creating a significant impact on daily transit service. We currently provide about 50,000 passenger trips each weekday.  Taking 75 buses out of our fleet would force a reduction in service of over 50 percent. This would most seriously impact the 30 percent of our riders who are transit dependent, including many elderly and disabled persons.  Omnitrans does not currently have another piece of property where the CNG fueling station could be moved to.

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What more can Omnitrans do to address our concerns?

Omnitrans is investigating the possibility of installing filters to mask or reduce the smell. Omnitrans is also soliciting bids for a liquid compressed natural gas (LCNG) fueling station at its Montclair facility with an option to install such a facility in San Bernardino.  CLNG would be stored in tanks on the property rather than brought in via gas company lines.  LCNG does not have an odorant such as methyl mercaptan added to it. Omnitrans would have the option of adding a less offensive odorant to the LCNG.  If this option were approved and funded, acquisition and installation still would take many months.  An LCNG station in San Bernardino would not replace the current CNG station, but would reduce its use and potential odor leaks.

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Omnitrans
1700 W Fifth St
San Bernardino, CA 92411
1-800-966-6428

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