46 CFR §154.901

1. (a)Each vessel must have a piping system for purging each cargo tank and all cargo piping.
2. (b)The piping system must minimize the pocketing of gas or air remaining after purging.
3. (c)For cargo tanks certificated to carry flammable gases, the piping system must allow purging the tank of flammable vapors before air is introduced and purging the tank of air before the tank is filled with cargo.
4. (d)Each cargo tank must have:
   1. (1)Gas sampling points at its top and bottom; and
   2. (2)Gas sampling line connections that are valved and capped above the deck.