在通风不良或封闭式的地下室、水池、坑道、深井、仓库、污水管、化粪池、挖孔桩、油罐、气罐等处施工，空气中常常积聚着一些对人体有害的气体，它们是无形杀手。从以往许多伤亡事故中得出教训，分析这些有害气体大致有下列几种。１．甲烷（CH４）无色、无味，本身毒性虽然很 In poorly ventilated or closed basements, ponds, tunnels, deep wells, warehouses, sewers, septic tanks, dug piles, tanks, tanks and other places of construction, the air is often accumulated in a number of harmful gases, they Invisible killer. Draw lessons from many casualties in the past, analysis of these harmful gases generally have the following. 1. Methane (CH4) colorless, odorless, although its own toxicity