Abstract: At approximately 11:35 a.m. on August 23, 1995, Employee #1 entered an 8.4 ft deep and 8 ft wide geothermal vault, with a manhole entry of 32 in., in an attempt to rebuild a pressure reducing valve. According to the Environmental Control Industrial Waste Section, the geothermal vault oxygen level content measured between 19.6 and 19.7 percent oxygen before any chemical substances were introduced into the geothermal vault. The measurements taken by the Environmental Control Industrial Waste Section were taken with a Gastech GX-82, serial #HX-13452, an oxygen meter without an extension hose. Employee #1 also used the Gastech GX-82 when he conducted atmospheric monitoring and he found levels between 19.5 and 19.6 percent of oxygen. After WD-40 and Graff-Off were introduced into the geothermal vault, the oxygen level dropped to 18.9 percent. Employee #1 complained of dizziness, nausea, and difficulty in breathing. He was diagnosed with pulmonary edema that later turned into pneumonia. The causal factors of the accident included the employer's failure to train employees in confined space entry and hazard communication. In addition, the employer did not provide the employees with a material safety data sheet for the products they used.