RE: Hood Face Velocity

["Aaron Chen 609-540-4448, 609-472-0046(cell)" <Aaron.Chen@usa.dupont.com>]

	Chuck,

	I would be very careful with just looking at face 
	velocity as determining if a hood of any type is "safe"
	to work in.  I would suggest doing some type of a
	quantitative or qualitative containment testing to assure
	that whatever face velocity you select actually does 
	protect.   Most folks, including ACGIH, ASHRAE and many
	hood manufacturers tend to suggest that 100 feet/min
	will work well in most instances.   But that is in most
	instances and there may be some other situations where
	the chemical toxicity TLV is so low or the set up of
	equipment in the hood may change that number.  This is
	where a containment test is useful to verify that you 
	can protect.  I would suggest doing it when working with
	highly toxic chemicals and/or radioisotopes.

				Aaron Chen
				DuPont Jackson Lab
				Aaron.Chen@USA.dupont.com
				(609) 540-4448