Abstract: Two electricians arrived at a manhole to work in an underground vault. One of them put the probe of his Gastech meter into the manhole with the cover in place. He made tests at the bottom of the 2.5 to 3.5 meter deep vault and about halfway down; all the tests were negative. The other employee began to remove the manhole cover with a cover removal tool. When the cover was about half off, an explosion occurred in the manhole. The employee removing the manhole cover, who was standing at the top of the manhole, sustained burns over his face and chest. He was admitted to the hospital in serious condition.