Section 153.254 - Cargo tank access(a) A cargo tank must have at least one covered manhole opening into the vapor space described in § 153.354 .(b) An access through a vertical cargo tank surface must be at least 60 cm by 80 cm (approx. 23.6 * 31.5 in.) and no more than 60 cm above a foothold grating, or surface on both sides of the access way.(c) An access through a horizontal cargo tank surface must be at least 60 cm by 60 cm (approx. 23.6 * 23.6 in.).(d) An access trunk must be no less than 76 cm (approx. 29.9 in.) in diameter.