Abstract: At approximately 11:00 a.m. on February 3, 2004, Employees #1, #2, and #3 arrived at a utility hole. They started venting the hole with a blower hose from one of the trucks and at approximately 11:30 a.m. they used a MSA Microgard meter to check the atmosphere. The meter did not alarm so they began work by first pumping out the water in the bottom of the hole. They then opened the case, changed the wires and closed the case. At approximately 1:30 p.m. two of the employees complained of light-headedness and nausea. They stated that they re-checked the meter, and noted there was no problem. When they came out of the manhole, they stated that their hearts were racing, and their pulse rates were elevated. At that time, they could smell exhaust fumes on their clothes. They used another MSA Microgard meter that was on site and as they began to lower it into the manhole, it began alarming. At approximately 1:50 p.m., they walked a half block to a Fire Station. They explained what happened to a fireman and he told them they should go to the hospital and they should contact their supervisor. They contacted their supervisor and then went to a restaurant to eat. Their supervisor contacted them at the restaurant at approximately 3:10 p.m. and told them that he would pick them up and take them to the hospital. They arrived at Davis Hospital and had blood taken in the emergency room. The carboxyhemoglobin level for two of the employee's was 18 and the third employee's level was 19. They were then administered oxygen and were admitted overnight into the hospital.