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What happened?
Workers were flushing a level bridle on a hydrogen sulphide (H2S) compressor knock out drum.
A temporary hose was used to route condensate/boiler feed water into the top of the level bridle.
A second temporary hose was being used to drain sour water from the bottom of the level bridle to a controlled sour water slop tank.
A worker opened a ¼ turn valve, which inadvertently released H2S to the ground/open atmosphere, instead of draining into the controlled tank.
A fixed monitor 160 feet/50 meters away began alarming, prompting the worker to attempt to close the valve.
The worker experienced symptoms consistent with H2S exposure.
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Why did it happen?
The worker forgot to close a low point bleeder from the bottom level bridle, causing H2S gas to drain to the sour water hose and then to the open atmosphere.
The worker’s H2S monitor was non-functioning.
No written steps in the procedure for processes involving toxic substances.
Less than adequate plan or process for clearing toxic substances.
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What did they learn?
Develop a written procedure for using toxic substances in processes.
Require specific plans for clearing and disposing of toxic substances if used in processes. Include hose selection, and prohibit the use of ¼ turn level ball valves.
Take steps to verify personnel H2S monitors are working before starting the task. Revise the site policy to make this a requirement.
Train personnel on the consequences of H2S exposure in training course. Embed this in existing training courses.
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Ask yourself or your crew
How can something like this happen here?
What are the consequences of H2S exposure? What could have happened if the fixed H2S monitor didn’t begin to alarm?
How do you test if your H2S monitor is functioning?
What are the correct steps in toxic service processes? Do we have a written procedure for this task?
How can we improve our procedures or processes?
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Published on 21/02/20
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During flushing of a level bridle on a Hydrogen Sulfide (H2S) compressor knock out drum, a worker was exposed to H2S gas.
