Air Quality Testing

There are a number of reasons why you might want to monitor indoor air quality in the workplace environment. These include:

• Making sure that substances which fall under the Control of Substances Hazardous to Health (COSHH) do not exceed set limits.
• Checking that control measures are actually working as they should.
• Helping to choose the appropriate level of protective personal equipment (PPE) for employees undertaking processes which may put them at risk.
• Complying with the advice given by Health and Safety inspectors to provide evidence of improvements requested.
• Assuring employees that their health and safety is a priority where potential hazards exist.

Air quality testing is not a substitute for controlling exposures. It is part of a comprehensive approach to controlling the air quality in your workplace. Levels of indoor air pollutants vary from day to day, so unless you have continuous monitoring, measurements may not give a true level of exposures over time. Furthermore, the data is only as good as the equipment used and the training of the person operating it. It goes without saying that where a consultant is being employed to do your air quality testing, then employees should co-operate with their work. The Health and Safety Executive has guidelines as to what should be contained in a consultant's air quality report – in short, the air quality data should be put into context so employer and employees understand what it means for them and can plan any action needed.

The World Health Organization estimates that nearly 3 per cent of the global burden of disease is attributable to indoor air pollution, including exposures in the workplace setting. We spend up to 90 per cent of our time indoors, at home, school or in the workplace. Poor indoor air quality can lead to a range of health issues, from occupational asthma to the poorly understood condition 'sick building syndrome.' For the employer, a failure to monitor and control workplace air quality can lead to:

• Employee health problems, leading to absenteeism and lost productivity.
• Low morale and high-stress levels among the workforce.

This will depend upon the workplace situation and the type of information you need on air quality. The testing regime may range from simple spot checks carried out on a regular basis by a designated trained employee to a detailed investigation done by a consultant. It may be necessary to install dedicated monitoring equipment to get a readout on air quality at all times, or regular spot checks may be sufficient. Health and safety inspectors and occupational hygiene consultants can advise what is needed for a particular workplace situation.

There are two main technologies – particle counters, and gas detectors.

Particle Counters

Particle counters determine the number and size of particles in the air. Further testing is needed to determine the identity of the particle if this is relevant. A particle counter uses laser counting technology. A sample of air is sucked into a chamber fitted with a laser beam at one side and a photodetector on the other side. As a particle passes through the chamber, it blocks the laser light and a signal is picked up by the detector. The nature of the signal is related to the size and number of particles and can be analysed to give this information. Laser particle counters can detect particles in the 25 to 0.1-micron range, which includes most dust, mould and bacteria. There are three kinds of particle counter:

• Handheld - These are good for 'spot' measurements but otherwise limited in their application.
• Portable - Can be left to work unattended, and so monitor particle levels over a period of time. Often linked to other environmental sensors and can store and print data.
• Remote - Usually part of a major environmental monitoring station and controlled by a computer.

Gas detectors

There are two main types of gas detector - electronic and gas tube. The electronic gas detector is best for a limited range of gases (e.g. carbon monoxide, carbon dioxide and oxygen levels), while the gas tube tends to be used for specific gases such as xylene.

The gas tube consists of an air sampling pump attached to a detector tube. A sample is drawn into the tube, which contains a detector dye capable of reacting in a highly specific way with the gas or vapour under test. The tube is designed so that the concentration of the gas or vapour is read off directly from a measurement scale on the tube. Adjusting the sample volume allows a wide range of gas concentrations to be measured. Gas tubes are available for measuring levels of several hundred different gases and vapours. Moreover, the modern gas tube is easy to use, accurate and gives rapid results.

In the UK, the Control of Substances Hazardous to Health (COSHH) regulations require control of substances that may pose a hazard to health. Some of these are hazardous by inhalation, so levels in the surrounding air need to be controlled. Air quality testing needs to look at whether levels of a hazardous substance is under the Workplace Exposure Limit (WEL). This is the maximum allowable concentration of a hazardous substance in the air, averaged over a period of time. The short-term WEL is the WEL over 15 minutes, while the long-term WEL is the average over 8 hours. The WEL for a particulate substance is given in mg/m3 while that for gas or vapour is given in parts per million (ppm).

The list of WELs covers around 500 hazardous substances and it was last updated in December 2011. This is only a fraction of the many thousands of substances which are used in various industries. Just because a substance does not have a WEL defined for it does not mean it is safe.

The WEL list notes when a substance is carcinogenic, causes asthma or is absorbed through the skin (if this is known). Exposures to any substance that causes cancer, asthma or genetic damage must always be kept to an absolute minimum under COSHH.

The broad categories of hazardous substances are:

• Chemicals
• Dust
• Vapours
• Microorganisms
• Gases 

All of these categories are airborne, so air quality monitoring has an important role in keeping under the WEL set.

Some of the substances you may have heard of that have a WEL include:

• Carbon black
• Cotton Dust
• Carbon monoxide
• Flour dust
• Grain Dust
• Hardwood and softwood dust
• Cement dust
• Silica
• Xylene

Dust of any kind (whether or not its components have a WEL) also has a WEL. Under COSHH, the inhalable fraction of dust must not exceed 10 mg/m3 and the respirable fraction must not exceed 4 mg/m3. Inhalable means dust particles getting into the nose and mouth and can, therefore, get into the lungs. Respirable means the fraction of this that actually gets into the gas exchange section of the lungs. A particle counter would be appropriate for measuring dust levels in the workplace.

There is now a very wide range of air quality testing equipment and many different air quality elements can be monitored. These include:

• Levels of particulate matter (PM)
• Hazardous gases including formaldehyde, ozone and carbon monoxide
• Thermal comfort – that is, humidity, air circulation and temperature
• Airborne bacterial and fungal contamination
• Carbon dioxide levels, to indicate fresh air circulation