The HSE can often be perceived as rather vague about whether airflow indicators should or must be fitted to LEV systems.
Is it a recommendation or a stipulation?
Many of you may know Bill Cassells. Bill has over 30 years experience in Industrial Ventilation both with HSE and as a private consultant. He owns the LEV training company Oxly8, and is widely regarded as one of the foremost authorities on the design, management and testing of Industrial Ventilation systems. He teaches the full range of BOHS P600 LEV courses, and also acts as an engineering Expert Witness for the UK Courts in cases relating to occupational respiratory diseases.
In this comprehensive article on his website oxyl8.com Bill discusses the use of airflow indicators to put their use into perspective, not only as a recommendation of HSG 258, but also as a means of complying with the broader legal requirements of COSHH.
Bill goes into some depth to fully explain the subject so you may want to make yourself a cup of tea before you start!