Abstract: At approximately 10:25 a.m. on August 25, 1988, Employee #1 was sent into a sewer manhole called a valve vault to open a valve. While in the vault, Employee #1 passed out. Employee #2, not knowing why Employee #1 had passed out, went down to help him. Once in the vault, Employee #2 passed out. Employee #3, who had seen Employee #2 enter the vault, decided that there might be bad air in the vault. He tied a rope around himself, then entered, tied a rope around Employee #2, and then passed out himself. Somehow, Employees #2 and #3 were able to get out of the vault. Employee #4, seeing that Employee #3 was dazed, took the rope off him and went into the vault but passed out before he could tie the rope around Employee #1 and had to be pulled out himself. When the fire rescue quad arrived wearing air packs they retrieved Employee #1, who was dead. Employees #2, #3, and #4 recovered.