Heather Mawhinney assesses the control mechanisms that should be used to minimise exposure to respiratory sensitisers.

Background

Each year thousands of people become ill and/or die from work-related diseases mainly due to past working conditions. In 2011/12 an estimated 35,000 individuals suffered "breathing or lung problems" which they believed to be work-related, according to the Labour Force Survey. This estimate includes respiratory diseases and occupational asthma. Such diseases can result from workers breathing in excessive airborne contaminants at work, often because control measures do not work well enough.

Most industries are affected, from scientific laboratories to foundry work, so the problem is widespread.

Conventionally, airborne contaminants, which are present in workplace air, are controlled using local exhaust ventilation (LEV) — extracting the contaminants before they are inhaled.

Purpose of LEV

The primary purpose of an LEV system is to remove or dilute a hazardous substance from the immediate workplace, and hence prevent people inhaling airborne contaminants that could cause short or long term damage to health. The LEV system will not eliminate the hazard, it just moves it to another location, nor will the LEV protect against contact hazards.

A well designed LEV will collect the air that contains the contaminants, ensure the contaminated air is contained and removed from people, clean the air (if necessary) and get rid of the contaminants safely.

Characteristics of LEV

LEV is an engineering control system. Most systems have some, if not all, of the following features.

  • Hood: where the contaminant cloud enters the LEV.

  • Ducting: conducting air and the contaminant from the hood to the discharge point.

  • Air cleaner or arrestor: filtering or cleaning the extracted air.

  • Air mover: powering the extraction system, usually by means of a fan.

  • Discharge: releasing the extracted air to a safe place.

Types of LEV

A typical LEV system works by drawing contaminated air from a process through a partial enclosure or hood at, or close to, the source of emission or contamination. The contaminated air is then drawn away and may be discharged into the air at a distant point (such as the rooftop) where the dilution effect of the atmosphere reduces the concentration to acceptable levels, or may be cleaned up (eg by particulate filtration) and then discharged to the environment.

There are basically two types of LEV: capture or extraction.

Capture systems are normally small local systems designed to provide point extraction. They remove the substance from the point of generation, to a filter pack or capture container.

An extract system is normally a larger system, often built into the building. This system will normally reduce the risk by dilution of the substance before venting it to atmosphere.

Legislation requirements

The principle legislation is the Control of Substances Hazardous to Health Regulations 2002 (as amended) (COSHH) and supported by the Provision and Use of Work Equipment Regulations 1998 (PUWER).

The need for a fume cupboard must be established by COSHH assessment; it must be considered when other means of control have failed to reduce the hazard, as per the Hierarchy of Control. Other options which should be considered before LEV are eliminating the source, substituting the material being used by something safer, reducing the size of the source, modifying the process, reducing the duration or frequency of the emission, reducing the number of employees involved in the process and enclosing the process.

When the need for an LEV has been established it must then be carefully selected. It is vitally important to match the hood to the source that needs to be controlled. It is possible to purchase “off-the-shelf” systems but it is essential to ensure they are fit for purpose and capable of adequately controlling exposure.

Selecting the right contractor is crucial; the supplier should be competent to do the job. On installation, the supplier should test the LEV to ensure it is working according to the specification. Commissioning should be carried out under normal working conditions and will prove if the LEV has been installed properly and that it controls exposure. On completion of commissioning, the supplier should provide a user manual, a logbook and a commissioning report together with training on how the LEV works and how to check and maintain it.

The COSHH regulations specify that:

  1. an employer who supplies a control measure to comply with the regulations shall ensure that it is maintained in an efficient state, in an efficient working order, in good repair and in a clean condition

  2. LEV plant provided to comply with the regulations should be examined and tested at least once every 14 months, (once a year is common practice)

  3. a suitable record of the examination and test should be kept for a minimum of five years from the date on which it was made.

The environmental permitting regime (England and Wales) and the pollution prevention and control (PPC) regime (Northern Ireland and Scotland) regulate emissions to air.

In general, emissions from fume cupboards are not likely to contain large amounts of chemicals. However, if a process uses organic solvents in particular, it may be necessary to check that the total quantity of solvents used across the site does not exceed certain thresholds. An environmental permit will contain details of limits on solvent emissions and how and when these must be met.

When emissions cause annoyance to the surrounding community, they may have to be dealt with as a statutory nuisance. A business regulated under the environmental permitting regime (England and Wales) or the pollution prevention and control (PPC) regime (Northern Ireland and Scotland) will have conditions that control emissions that could be a nuisance, such as noise, dust or odour, contained in their permit.

The design and fitting of fume cupboards should comply with British Standards. Depending on the age of equipment, it should be built and fitted in compliance with BS 7258:1994 or BS EN 14175:2003. These standards set out the safety and performance requirements and specify that the air being drawn into the fume cupboard has an average velocity of 5m/s and that the minimum velocity at any point is 4m/s or greater.

Requirements for specific types of fume cupboard

A fume cupboard for work involving radioactive substances must be fitted with a filter and be labelled as a “Filtered Fume Cupboard”.

A fume cupboard for work involving reactive materials, such as hydrofluoric acid, which can damage pipework and the cupboard itself, should be fitted with cascading water over the airflow outlet and be labelled as a “Scrubbed Fume Cupboard”.

Filters from fume cupboards must be treated and disposed of as hazardous/special waste. Contaminants can be identified with the aid of Safety Data Sheets (SDS).

Fume cupboard good practice

  • Plan carefully and aim to minimise the use of materials and reduce both emissions and waste.

  • Never use fume cupboards to store chemicals, as this will avoid accidental spills and unplanned reactions.

  • Always ensure that containers have lids securely fixed in place.

  • Keep appropriate spill kits in the vicinity.

  • Be aware that fume cupboards do not provide complete containment and use a glove box or glove bag if further protection is necessary.

Last reviewed 30 January 2013