What’s wrong with captor hoods?

Captor hoods are one of the most common types of inlet that you’ll find on extraction systems. With these hoods, the contaminant is generated and disperses outside the hood. It has to be drawn into the system by the airflow. Unfortunately, in most cases, they are largely ineffective at controlling contaminants. The following diagram illustratesContinue reading “What’s wrong with captor hoods?”

Testing LEV systems when baseline data isn’t available

One of the main problems we encounter when carrying out a thorough examination and test of a local exhaust ventilation (LEV) system is the lack of “baseline data” – i.e. information on what the pressures and velocities should be when the system is operating in accordance with the design specification. Providing the system has beenContinue reading “Testing LEV systems when baseline data isn’t available”

Managing LEV systems – have things improved?

Yesterday I went over to the Health and Safety laboratories for a “stakeholder meeting” with HSE/HSL to discuss a potential new one day course on the management of local exhaust ventilation (LEV)systems. It was a good meeting and I feel that HSE were willing to listen and take on board suggestions that I and otherContinue reading “Managing LEV systems – have things improved?”


When you’ve been working in a particular profession for a while its easy to forget how confusing terminology can be. I find that although we take for granted what is meant by “local” and “general” ventilation, the meaning is not necessarily obvious to someone new to occupational hygiene or to non-specialists, such as managers andContinue reading “Jargon”

P601 – Competence in LEV testing

I received the following query a few days ago: A large part of my working life during the last 14 years has been involved with the Thorough Examination and Test of Local Exhaust Ventilation (LEV) systems within the company I work for. I have now moved on within the same company to a health and safety position,Continue reading “P601 – Competence in LEV testing”

The joys of LEV testing – Part 1

I’ve been out on site this week with Deb, getting our hands dirty doing some ventilation testing. A number of the systems were quite large, with several hoods and branches. Most of the hoods couldn’t be reached when the process is operating due to safety considerations. This makes testing difficult. It’s only possible to measure face andContinue reading “The joys of LEV testing – Part 1”

Stack Heights

When designing and testing local exhaust ventilation systems we need to pay particular attention to the design of the extraction hoods – where the contaminant enters the system. If this isn’t right then the system is unlikely to be effective at controlling contaminants. However, this doesn’t mean that we shouldn’t ensure that other aspects ofContinue reading “Stack Heights”