When a vessel is carrying acetaldehyde, butadiene, ethylene oxide, or vinyl chloride, the master shall ensure that air is:

1. (a) Purged from the cargo tanks and associated piping before the cargo is loaded; and

2. (b) Excluded after the cargo is loaded by maintaining a positive pressure of at least 13.8 kPa gauge (2 psig) by:

   1. (1) Introducing a gas that:

      1. (i) Is not reactive;
      2. (ii) Is not flammable; and
      3. (iii) Does not contain more than 0.2% oxygen by volume; or
   2. (2) Controlling the cargo temperature.