That’s a common question. If there was a good, all-purpose answer to it, we’d make sure it was in every data sheet and on every Web page. Unfortunately, physical area isn’t the limiting factor in all cases.
The gases that mix well with air (CO, CO2) can sometimes be treated by area because they fill the space at a constant rate when they’re introduced, as long as barriers aren’t substantial. So for an open area, manufacturers will say their sensor has a “50-foot surveillance radius” or covers “5,000 square feet,” or something else that pretty much covers liability from the manufacturer’s perspective. That’s OK.
However, for gases that are either much lighter than air (methane, hydrogen, helium) or much heavier (most refrigerants, butane, propane, etc.), the placement of the sensor really has to be engineered.
If your customer has a chiller full of R-134A and it springs a leak, the gas will fall to the floor and spread just like water. If there’s a trough in the room, or a curb, or another obstruction, the gas will stop there and stack up until it flows over it. You need to observe the room and pick the best spot to put the sensor to catch the leak in the shortest amount of time. Low spots are the best bet, and the closer to the machine, the better. If there are multiple machines in a giant room, I wouldn’t get more than 25 feet from any given machine.
If you’re watching for methane (or natural gas) in a closed space, find the high spot for your sensor. Any leaking methane will head there first. Once you’ve found the high point, go find the building owner, the architect, the engineer, or someone in authority and ask why the heck they don’t have a vent in that closed room when there could be a potential leak.
Just think those gas sensor placements through before simply applying a square-foot-per-sensor rule to them. And call Kele—we’ll be glad to help.