46 CFR §197.322

1. (a)Each surface-supplied helmet or mask must have—
   1. (1)A nonreturn valve at the attachment point between helmet or mask and umbilical that closes readily and positively;
   2. (2)An exhaust valve; and
   3. (3)A two-way voice communication system between the diver and the dive location or bell.
2. (b)Each surface-supplied air helmet or mask must—
   1. (1)Ventilate at least 4.5 ACFM at any depth at which it is operated; or
   2. (2)Be able to maintain the diver's inspired carbon dioxide partial pressure below 0.02 ATA when the diver is producing carbon dioxide at the rate of 1.6 standard liters per minute.