> Architects are telling us that hoods with a combination sash (that can work horizontally or vertically) are
> available and would be better for students who need accommodations. Does anyone have experience with this kind of fume hood? What are the advantages/disadvantages of the combination sash fume hood?
From a safety and EHS point of view, I have more experience with the disadvantages than the advantages. The disadvantages are:
1. Workers will essentially always use the horizontal sliding option rather than the vertical option when moving the slash. This means that they open up the hood face in a way that provides a direct path for wayward chemicals to the person‰??s face. It also means that it is much easier to lean into the hood to make adjustments to the process (following the ergonomics rule that posture is driven by vision needs).
2. Providing effective training in how to most use a hood is significantly more complicated for combo hoods that vertical only sashes. The designer‰??s suggestion that the vertical pane be used as a shield is ergonomically problematic, at best.
3. For VAV systems with combo sashes, the control systems that adjust the face velocity are much more complicated and likely to confuse both hood users and the maintenance staff with random alarms which are ignored or silenced.
4. From an periodic hood certification point of view, establishing a reproducible protocol for combo sashes is more complicated.
5. I‰??m unconvinced that redesign of the hood, and the resulting mechanical complications associated with the ‰??ADA hoods‰?? is the best way to provide accommodations to students who need them. There are many conditions that could require accommodation and the ability to sit while working at the fume hood, which seems to be the only accommodation envisioned in hood re-design, raises many safety questions in my mind.
The sustainability advantage of combo hoods is that they can reduce the total air volume required to maintain face velocity because the open face area when it is being used is smaller.
Ralph Stuart, CIH, CCHO
Chemical Hygiene Officer
Keene State College
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