From Scp Wiki
Item #: SCP-819
Object Class: Keter
Special Containment Procedures: Item SCP-819 should be stored in a completely airtight and oxygen-evacuated area. At no time may oxygen make contact with the surface of SCP-819, so an airlock is also required. Personnel entering SCP-819's holding area should first be wearing standard-issue breathing apparatus. Should the oxygen tanks of any personnel be breached while inside the chamber of SCP-819, the inner airlock door will be opened, but the outer door will be locked down for a minimum of 3 hours. Once the 3 hours have expired, all remaining personnel inside the airlock will be released. There is no minimum or maximum limit for personnel. There is no minimum or maximum time limit for being inside the chamber. Anyone who is suspected to be affected by SCP-819 is to be quarantined immediately for a period of no less than 24 hours.
Description: Moved to Site 7 April 10, 2002. Found in the Pyrenees mountains. SCP-819 resembles a small fleshy sac approximately the size of a handbag, with several slits along each side that scientists are fairly convinced act as gills. When SCP-819 "breathes" in oxygen, it converts it into an anomalous gas and immediately exhales the gas in a large puff. Any human or animal that inhales the gas will show no symptoms for fifteen minutes to an hour and a half, but afterwards their abdomen will swell up and burst in a matter of seconds via a mechanism that is yet undetermined. The victims usually die instantly. The strange gas exuded by SCP-819 converts to oxygen, sulfur, nitrogen, and hydrogen after a short period of time, making study of the chemical makeup difficult. It should be noted that the victims of the gas release an entirely fresh batch of gas once they are killed by it.
Addendum: Following the events led by ███████ ██████'s exposure to the gas released by SCP-819, which resulted in [DATA EXPUNGED], the minimum quarantine time has been increased to 24 hours.