The work of breathing or WOB is in simple terms, the effort required by the lungs to breathe. But to be more accurate it refers to the energy expended to inhale and exhale a breathing gas. The WOB is usually expressed as work per unit volume.
Divers Alert Network or DAN is a non-profit agency that collects and analyze information for divers safety. It has branches that sell different diving oriented services and products such as insurance or oxygen providing kits or First Aid and CPR courses.
fsw or feet of seawater is a measurement unit of the imperial system and represent the pressure in 1 foot of seawater or about 15 psi. 33 feet is also roughly 1 atmosphere.