Abstract: Employee #1 entered a semi tanker trailer to wash out the inside, which had contained a fatty acid (linseed oil). A short time later, he was found lying at the bottom under the hatch opening. Employees #2 and #3 jumped in to rescue him and were nearly overcome. Employee #1 died, and blood tests conducted two hours after exposure revealed carboxyhemoglobin levels of 56 percent for Employee #1, and 15 and 25 percent for Employees #2 and #3, respectively. The vessel's atmosphere was later found to be an inert gas containing mostly nitrogen and about 5 percent carbon monoxide. The gas had been made by the plant that unloaded the trailer, and had been used to blow off the load. When the driver arrived at the truck washing facility, he had not informed the workers about the inert gas, nor had the manifest indicated its use. The tank washing facility had not tested the atmosphere in the tank before Employee #1 entered, and there was no confined space entry program in effect.