What happened? (Spring 1990) An attempt was made to remove a regulator from a cylinder of hydrogen sulfide, which had been in sporadic use for 7 years. Upon loosening the regulator, hydrogen sulfide began to leak from the cylinder, even though it was thought the main valve had seated properly when closed.
The regulator was re-tightened on the leaking cylinder and Risk Management & Safety (RM&S) was contacted. At this point, only the regulator was containing the gas in the cylinder. RM&S took possession of the cylinder, eventually closed the main valve with considerable difficulty, attached a brass cap in place of the regulator and returned it to the distributor.
Why did it happen? During the time the cylinder of hydrogen sulfide was connected to the regulator, the main valve was left open and the gas flow was controlled only by the regulator. Because the main valve was not operated for long periods of time, the valve partially froze and could not be completely closed.
How can a similar occurrence be avoided? Main valves on compressed gas cylinders must be closed when not in use. This is particularly important when using gasses such as hydrogen sulfide which may corrode critical valve components. Use a flow control valve to regulate flow – a regulator is for pressure control.
Note – Hydrogen sulfide is an extremely hazardous chemical that requires prior approval (Chemical Safety Level 3 or CSL-3) by the Institutional Chemical Safety Committee (ICSC). For approval, the Minimum Requirements for Toxic/Corrosive Gas Use (PDF format) will at least be required by the ICSC.
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