Fume Hood Ventilation requirements

Fume hoods are used in wet chemistry operations to prevent exposure to vapors . There are many guidelines on what is the minumum face velocity that is required for protection (e.g. 100 ft/min . 80 ft/min). Does anyone have any experience or references of what meets the minumum requirements for safe operations ?

 

[KenRad]

If we are talking about laboratory fume hoods that are used for containment and exhaust of hazardous vapors, my experience has been a range of 60 - 100 FPM on face velocity. There are many factors which determine where you want to be in that range, including the degree of hazard involved, as well as the presence room air currents near the hood face which can disturb the face velocity. Face velocities much higher than 100 FPM can cause turbulence which can actually be detrimental to containment of the vapors.

Some good resources for fume exhaust include the book "Industrial Ventilation," published by the American Conference of Governmental Industrial Hygienists, and the ASHRAE Handbook Chapter 13.

 

[ChasBean1]

I agree with KenRad, but this is a manufacturer issue. If you buy a wood stove that doesn't remove smoke, I wouldn't look in an ASHRAE book, I would call the maker. Some hoods might be good down to 40 fpm or less, but room supply air movement and turbulence at the face can often be higher than that... ASHRAE-110 gives the testing standard, AIHA (ANSI-Z9.5) is the basis.

 

[fredb]

Hi wrbarkey

The American Conference of Governmental Industrial Hygienists Gives the following requirements:

Exhaust Volume
1. 100cfm/sq ft of door area for nuisance, corrosive materials. Moderate toxicity materials, tracer quantities of radioisotopes.

2. 150cfm/sq ft of door area for High toxicity materials (TLV equal to or less than 0.2 mg/cubic meter), Low MPC radioactive materials.

3. Glove Box (Dry Box) for very high toxicity materials. (Pathogenic microorganisms).

 

[ChasBean1]

wrbarkey/fredb - just be careful of the "150 cfm/ft2 of door area for high toxicity materials." Most hoods' performances deteriorate significantly up in that range. Most perform best at 70-110 fpm without flow disturbances (e.g., air throw from diffusers, people walking by, etc.). Cranking up hood exhaust flow usually means worse capture (see KenRad's post above).