In a non-anesthetizing area, on which side of a zone valve should the area alarm pressure/vacuum sensor be located?

• A. NFPA 99 does not specify a requirement
• B. upstream side
• C. station outlet/inlet
• D. source

Answer: (C)

The key idea is that area alarm sensors must monitor pressure or vacuum at the boundary where the zone valve separates the protected area from the rest of the system. For a non-anesthetizing area, placing the area alarm sensor on the station side of the zone valve—specifically at the station inlet/outlet side—ensures the sensor reflects the actual conditions in the area being served. If the valve isolates the zone, the sensor on the boundary will detect whether the area is adequately pressurized or if a loss occurs, triggering the alarm appropriately. Placing the sensor upstream of the valve would not detect issues inside the protected area once the valve is closed, and locating it at the source wouldn’t reflect the local conditions of that zone. NFPA 99 requires monitoring on the non-anesthetizing area side at the valve boundary, which is why the station inlet/outlet side is the correct placement.