gas test leak atmosphere confined space warning sign permit entry by permit only and red barricade danger tape

accident asphyxiation atmosphere atmospheric authorization background barricade barrier book business caution concept confined construction controlling danger dangerous defocused detector discretion editorial emissions enforcement entry environment equipment forbidden gas h2s hazardous health industrial industry inspecting inspector invention isolated leak machine manhole monitoring occupation only operator pen permit permitting professional protection red restricted safety security severe sign space supervisor tape technology template test warning yellow