Clients often ask me if they should provide continuous gas detection in their laboratory hoods. I always start by asking them why they believe it is necessary and usually get some version of the following. (These are numbered for reference not any priority.)
- To warn them they have a leak or similar loss of containment.
- To warn them their scrubbing, neutralization, or treatment systems are not working properly.
- To allow them to lower the area electrical classification inside the hood to unclassified (AKA general purpose or ordinary).
- To warn them “something” happened inside and alert the operators that they may be at risk.
The issue with any gas detection in a hood is dilution. Assume a fairly typical 4 ft long benchtop hood with a vertical sash designed for a maximum 24” opening and an average hood face velocity of 100 ft/min. This hood would require at least 800 CFM. That means you are going to need a lot of leakage to get to a detectable level. Look at these examples:
