LEV.

LEV catches dust, fume, mist or vapour where it is released and takes it out of the room: a hood placed close to the source, ducting, an air cleaner, a fan, and a discharge. A fan in the wall is not LEV. It dilutes, and it drags contaminated air past the operator's face on the way out, which is the opposite of capture. HSE treats an LEV system as something that has to be proved rather than owned, so the employer must keep its performance up and arrange a thorough examination and test at least every 14 months, with airflow indicators at the hood recommended because the usual failure is a slow loss of flow nobody can see. On a print floor that means the powder shaker's extraction, the screen wash booth and the dryer stack, and it means somebody reads the indicator at the start of a shift rather than after a complaint. A hood knocked out of position, or a duct half-packed with adhesive powder, still hums and still looks like it is working.