gas leak test atmosphere detector at confined space permit manhole entry door

accident adult application asphyxiation atmosphere atmospheric attention authorization background banner barricade barrier business caucasian caution concept confined construction controlling danger dangerous design detector discretion emissions enforcement entry environment equipment forbidden gas granted greenhouse h2s hazardous health helmet industrial industry inspecting inspector invention legal machine manhole monitoring natural nature occupation operator people permit permitting professional project protection provisions restricted safety scanning security sensor severe sign site space striped supervisor technology test tool warning work worker