Posted By Mike Beckett With the amount of deaths that occur due to nitrogen asphyxiation I am interested to know if anyone has investigated the possible use of odourant in Nitrogen when purging vessels and pipelines ? Any such additive would need to be non poisonous to catalysts and acceptable to local communities when venting.

Posted By Mike Beckett Sorry, perhaps I should have been more descriptive in my initial question. I work in the oil industry where it is common practice to use large amounts of nitrogen in a gas state to purge vessels and pipelines for either hydrocarbon freeing prior to maintenance or oxygen freeing before introducing hydrocarbons. One of the more common incidents that we hear about is when a vessel is open to atmosphere for maintenance but has a small nitrogen purge to prevent oxygen ingress. Someone then inadvertantly put a tarpaulin cover up because its raining and creates a confined space which fills with nitrogen.We have many procedures in place to control access, but there is always that one person who makes a quick decision to keep the job going without realizing the risk. Now if you could smell the nitrogen that must surely be safer. Mike Beckett

Posted By Bob Pedley Mike, I have had extensive experience in using nitrogen within the oil and chemical industries for the uses you are familiar with. I agree there are hazards and I have been involved in investigating a serious incident involving the same where we considered introducing an agent. Stenching agents (usually a form of mercaptan), if you could introduce them would probably cause more problems than the known hazards associated with nitrogen, given the typical volumes of products involved and the amount of agent that would be required . Think about how you would purge the vessel or equipment. With just nitrogen you simply purge to air, with a stenching agent you would stink the site out. This could become an environmental nuisance even if it wasn't a safety hazard. For leak detection following a shutdown searching odourless inert gas mixtures are used. To make that job easier, if it was viable I guess someone would have introduced a stench if possible. (NOWSCO was the company we used for this activity). Unfortunately I think we are stuck with the usual permit controls for now. Unless some of the new chemicals used in "air freshners" could be adapted, I have wondered about the general safety of those things these days! I would be interested if you come up with a solution, it could be quite an innovation if you succeed. Bob