Best Practice for LEV Hood Design

Research undertaken by the Health and Safety Executive (HSE) has shown widespread evidence of overconfidence in the level of effectiveness of local exhaust ventilation (LEV) systems design.

Poor hood design is seen as the most common cause for ineffective LEV systems operation. It is ironic that designers pay little attention to the design of the hood as this is normally the part of the system with the lowest cost, however it will be determining factor as to whether a system will work or not. The result is a LEV system that does not control contaminants and risks exposing employees to harmful dusts or fumes on a daily basis.
The HSE released a technical guidance document, HSG 258, to improve best practice within the industry. A requirement of this is that designers to undergo a proficiency test (module P602) to improve competency in LEV design. Unfortunately industry designers are slow on the uptake, resulting in a continual stream of new systems being installed which fail to conform to the COSHH Regulations.
To control airborne contaminants, we must first fully understand their properties, the processes involved, emission sources and how the operator physically carries out the tasks involved. The hood selection must match the process involved. Designers are required to verify the workplace exposure limit (WEL) before undertaking a design. WEL’s may be obtained from the HSE guidance tables, EH40.

The more the  hood is able to enclose the source of contaminant, the more effective the extraction system will be. A partially enclosed hood can reduce the requirement for airflow rate by up to 100 fold. The benefits to this reduction in airflow are decreased energy consumption, capital costs and increased protection of the operators.

The correct capture and face velocity should be applied to the hood and is dependent on the process or task being carried out. The capture velocity is defined as “the velocity required at a contaminant source to overcome the movement of the contaminant cloud and draw it into the hood.”

For over 10 years, MECHON’sability to provide cost effective and environmentally responsible solutions has been proven time after time. A failing system can be redesigned to improve performance without the requirement for additional air, filtration or power consumption.

MECHON are able to offer no-obligation consultation on:
. Existing system analysis for compliance and expansion
. Hood redesign and installation
. Redesign and rationalisation of systems to reduce power consumption and maintenance costs
. Stack Emission calculations (TGN-D1, Dispersal)

This ability stems from an accumulation of decades of industry experience, MEng & BEng qualified engineers and industry accredited qualifications that include BOHS, CIBSE, and IOA. Energy saving considerations including recirculation of filtered air are made as standard in all Mechon system designs.

Mechon are able to offer a free, no obligation consultation on:

  • Existing system analysis for compliance and expansion.
  • Hood redesign and installation.
  • Redesign and rationalisation of systems to reduce power consumption and maintenance costs.
  • Stack Emission calculations (TGN-D1, Dispersal)

This ability stems from an accumulation of decades of industry experience, MEng & BEng qualified engineers and industry accredited qualifications that include BOHS , CIBSE, and IOA.Energy saving considerations including recirculation of filtered air are made as standard in all Mechon designs.