The joys of LEV testing - Part 1

Quite often when testing a local ventilation system it isn't possible to access the hoods when the process is operating due to safety considerations. Many woodworking processes fall into this category, but there are plenty of other situations where this is the case. It's only possible to measure face and capture velocities when the process isn't running and as the process itself will affect the airflow, measurements taken when the process is down are not representative.

In such cases it's often best to measure the static pressure behind the hoods (in a location that can be accessed safely) but the results are only meaningful where there is data from an initial evaluation obtained when the system is performing as intended and when it is known that control is being achieved. You also need to know what variance in pressure is acceptable (i.e. at what pressure the system stops being effective). Of course, most companies do not have such data!!