Fume Hoods in Rad Labs -Reply

[FRAMEP@ORAU.GOV]

Denny wrote in part:

>The architect is inquiring about specs for the fume hood, primarily
>material of the surfaces and ductwork.  My thinking is sheet metal
>of the normal thickness for ductwork.  Seamless would be great, but
>I don't whether that is cost effective or not.
>Any thoughts?

The suggested ACGIH reference is good: Industrial Ventilation: A
manual of Recommended Practice, 22 nd ed. 1995. Also, it is dirt
cheap for what you get.

Also:

ANSI/AIHA Z9.5 Laboratory Ventilation 1992. Its got a lot of good
stuff in it! Expensive, but get it. 

The latter recommends the use of ANSI Z9.2-1979 "Fundamentals
Governing the Design and Operation of Local Exhaust Systems"
for determining duct requirements. Alas, I have not a copy but if I
were in your position, I'd get one.

But an old ERDA document I do have, "Nuclear Air Cleaning Handbook"
ERDA 76-21, UC-11, 70, recommends values for sheet metal thicknesses
for various ducts under negative pressure.  The recommendation
depends on the pressure, diameter and spacing between reinforcement.
Assuming an 8 to 12 inch round duct at minus 8 to 12 inches of water,
the recommended sheet metal would be 24 to 16 gage U.S. That might be
a little overkill. 

Sheet metal for the ducts sounds fine as long as there are no highly
corrosive vapors being vented.  The ACGIH document recommends average
flows according to the nature of the material being transported. 1500
fpm is usually recommended as the minimum, 2000 fpm to 3000 fpm are
common. Like you, ANSI Z9.5 likes seemless. For the hood lining
itself I'd be partial to stainless steel although that is not the
only option. 

Best wishes

Paul Frame
Oak Ridge Institute for Science and Education
Professional Training Programs
framep@orau.gov