I would like to "piggy-back" on this conversation a bit and also ask a question. We recently underwent a full control systems and alarm upgrade for all of our hoods on campus.  About 25% underwent a full hood replacement while the remainder had controls, VAV boxes, displays, sash sensors, and proximity sensors added or replaced. 

The plus side to this is that centrally, I can pop onto our BMS system and get an graphical representation of sash heights, flows, etc.  The downside is that now that we have functional alarms, they alarm a whole lot more (this is not actually a downside, but my researchers interpret it as such).  I have taken a two prong approach to this:

1.  If an exhaust fan serving the building goes offline or if there is a significant drop in static pressure within the ducts, our central plant gets an emergency alarm, including strobes, that a science or engineering building has a possible exhaust failure and facilities responds immediately.  The system automatically emails me as well, so that I can pop in and check on things either remotely or, depending on circumstances, in person. 

2.  Any lab-wide purge button use sends a notification to EHS. 

3.  For localized, low flow alarms on the hoods, the labs usually handle those.  They are trained to ensure that their sash is closed as soon as possible to 18" or below when in alarm.  If it continues to alarm, then a work order should be submitted for EHS and Facilities to look into the issue.   In actuality though, I have a few labs that simply mute the alarms constantly and continue working. 

My question is this:  We are pushing exhaust capacity limits in our chemistry building.  For my old school organic synthesis lab, they run columns all day, everyday.  Because of this it is very routine for the sash heights to be above 18" during column loading for extended periods of time.  This usually causes the hoods to be in alarm as they end up with a face velocity of 50-60fpm at those heights (our set points for alarms are 80fpm).  The hoods still maintain containment based on smoke testing, but the alarms are extremely uncomfortable for the labs and they end up muting them quite often.   Does anyone have thoughts or suggestions on this?