The requirement that Airflow Indicators (Pressure Gauges) should be fitted where possible to all extraction hoods is clearly spelt out in HSE guidance HSG 258 and INDG 408.

The guidance states 'The client needs an airflow indicator at every hood. That is because the operator needs some simple indication that the hood is working. The air flow meter must indicate simply and clearly when the air-flow is adequate.'

The rational behind the requirement for air indicators is that LEV systems like any mechanical system will wear out.  LEV system have ducting that can leak, dampers that move over time, filters that can break and rotating fans that wear out it is therefore inevitable, if nothing is done, that their performance will degrade over time.

The way LEV systems work usually mean they don't suddenly and completely fail. Usually the airflow rate falls off slowly over time without anyone noticing.   Slow change over time is difficult to spot but air flow is particularly difficult to assess because we humans are not design to measure airflow, the best we can normally do is 'is it flowing or not' and not how much. As airflow starts to fall away a person using the systems will notice a decrease in airflow until the failure to control exposure is  obvious. By the time failure is noticed over-exposure may have been occurring for weeks if not months. The only practical way an operator, or supervisor, can tell that a LEV system is likely to be operating effectively is by seeing that the hood is known to be drawing the required volume of air.

Can I tell if a LEV systems is working by the noise it makes?
The sound of an LEV system is the same over a wide range of volume flow rates (unless the system is completely blocked) this makes using sound levels a poor way of assessing airflows.

Can I use the feel of air over the front/back of my hand to judge airflow at a LEV hood?
It isn't usually possible to measure airflow rates 'by hand' this measurement is very much an off/on type of feeling on the hand and no good for determine true airflow volumes.

How can I gauge airflow?
To gauge the volume of air flowing into an LEV hood the operator or supervisor (or other person) needs some form of airflow indicator. This requirement is clearly spelt out in HSE guidance HSG 258 and INDG 408.

Enviro Safety Partnership can calibrate and install airflow indicators at LEV hoods.  If you would like more information please get in contact.