Abstract: At approximately 11:35 a.m. on August 23, 1994, Employee #1 entered a 8.4 ft deep by 8 ft wide geothermal vault with a 32 in. wide manhole entry to rebuild a pressure reducing valve. Before any chemical substance was introduced into the vault, the oxygen level was between 19.5 and 19.6 percent. Atmospheric testing was conducted by the EC unit and by Employee #1 using a Gastech GX-82 oxygen meter, serial #HX-13452, without an extension hose; the oxygen levels found were between 19.6 and 19.7 percent. After WD-40 and Graff-off were introduced into the vault, the oxygen level dropped to 18.9 percent. Employee #1 also noted hydrogen sulfide levels of 8 ppm. Employee #1 complained of dizziness, nausea, and difficulty in breathing. He was diagnosed as having pulmonary edema, which turned into pneumonia three weeks later. The casual factors of this accident include the employer's failure to provide employees with confined space and hazard communication training and with the material safety sheet for the product used in the confined space. The chemical constituents of WD-40 include aliphatic petroleum distillates and A-70 hydrocarbon propellant; the chemical constituents of Graff-off include isopropyl alcohol and 40 percent toluene by weight.