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When do you have to apply "lethal service"?

When do you have to apply "lethal service"?

When do you have to apply "lethal service"?

Dear all,

ASME defines very well what to do in case of "lethal service". Unfortunately, there is no guideline under which conditions (substances, concentration, temperature etc.) the requirement of "lethal service" have to be used.

Are there government regulation when to apply lethal service?
Is it up to engineers, to decide which equipment requires "lethal service"?

RE: When do you have to apply "lethal service"?

Do a keyword search for 'lethal', this has been discussed before but I can't seem to get the link here to show up correctly.  Also, there was another reference someone posted to substances considered 'lethal' by a government agency which I'm trying to find.

At the end of the day, it's up to the company to define what they want to consider as lethal substances even though that open you up to questions later by Regulation Agencies.

RE: When do you have to apply "lethal service"?

Various govt. agencies have stipulated the lethal (limits) for various materials at different conditions.  You can find that info on the ineternet.

RE: When do you have to apply "lethal service"?

Theoretically, if a leak of the substance contained within the pressure vessel is lethal to anyone exposed to the leak, the vessel should be designated "Lethal Service". However, the ASME Code makes it the responsibility of the Owner/Operator of the vessel to designate the service "Lethal". In practise, this does not happen - especially in H2S service where prolonged exposure to as little as 100 ppm can cause death. Some operators are afraid to designate a vessel "Lethal Service" for insurance and legal liability reasons. However, I believe that their failure to do so could cost them big time if someone died as a result of a leak. This should be covered more thoroughly by ASME or government regulations.

G. Gordon Stewart, P.Eng.
Gas & Oil Process Engineering Consultant

RE: When do you have to apply "lethal service"?

In Australia, Australian standard AS4343 specifies the severity of a good number of substances. The definitions are tied in with the Pressure Vessel and Pressure Piping codes.

A lethal substance is defined by AS4343 as a very toxic substance or highly radioactive substance which, under the expected concentration and operating conditions, is capable, on leakage, of producing death or serious irreversible harm to persons from a single short-term exposure to a very small amount of the substance even when prompt restorative measures are taken, usually with an exposure limit <= 0.1 ppm by volume (or equivalent) to NOHSC:1003. Examples include phosgene, sarin, acrolein and chloropicrin…

There are other classifications used by the Australian pressure equipment codes: Very harmful (eg chlorine, H2S), Harmful (eg high temperature steam, krypton), Non-harmful.

Of course AS4343 does not preclude engineering judgement. For example, CO2 is defined as non-harmful. But if it is part of a fire suppression system fed into a confined space, then in my experience, some aspects of the system may be subjected to more stringent safety requirements.

I hope this is helpful, but be careful "cross-pollinating" codes, as the detail of the safety requirements does not always correspond exactly.

James Wheeler

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