The ASME Code defines “lethal substances” as poisonous gases or liquids of such a nature that a very small amount of the gas or of the vapour of the liquid mixed or unmixed with air is dangerous to-life when inhaled.

Aromatic plants provide plenty of challenges in this respect.  For example, Jord supplied 64 air coolers to a Benzene, Toluene and Xylene (BTX) plant in Thailand where there were a number of lethal services. Another project involved natural gas production air coolers in Oman, where an unusually high level of H2S was expected. For projects such as these, attention to detail is everything.  In particular, the provisions of UW-2 in ASME VIII-1 must be complied with in their entirety.