After taking the boating safety courses
http://www.uscgboating.org/recreatio...ty-courses.php
Here is my take.
Always run blowers 5 minutes before cold starting engine(s). Sniff test the exhaust. If the gas presence is heavy visually check the engine compartment.
Blowers should be off during refueling. After the gas hose is put away, run the blowers before starting engine(s).
Cost Guard approved bilge blowers should not spark on initial start up to cause an explosion. Marine grade starters are suppose to be spark resistant although I heard otherwise from mechanics.