Does a list exist, where the gases and liquids are classified as lethal or none lethal? Is toxic the same as lethal?

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Not in ASME Code.
It is responsibility of the User to state whether the pressure vessel is in lethal service or not. Toxic (I see it applied by Engineering, for their proper use in accordance with their specifications, I presume), does not mean lethal.
Mauro.

Aussie,

Please read the footnote to UW-2, that is ASME definition of LETHAL.
With respect to a list, this depends on the location of installation, Ammonia for example is considered lethal in some places, in others not.

The Owner shall specify whether or not it is L. and do not forget the nameplate stamping.

Best greetings to "down under", Bavaria from Prussia.

DK.

Check oou AS4343