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Indoor Air Quality Monitoring

Indoor Air Hygiene is currently regulated by both COSHH and Workplace Regulations 1992. Companies should be able to demonstrate that the air does not contain substances hazardous to health and that ventilation systems are regularly and properly cleaned, tested and maintained.

Paragraph 33 of the Workplace (Health & Safety Welfare) Regulations 1992 requires that:-

“Mechanical ventilation systems (including air conditioning systems) should be regularly and properly cleaned, tested and maintained to ensure that they are kept clean and free from anything which may contaminate the air.”

The key analyses that should be carried out are:-

1. Airborne Microbiological Sampling

This is carried out by a device drawing a pre-determined volume of air over an exposed nutrient plate so that airborne bacteria and fungi are impinged onto the medium and captured.

While there are no specified levels of airborne bacteria and fungi for a general uncontrolled environment the makers of the equipment propose a number of classes of total microbial count per cubic metre. For an office environment the following results are normally considered acceptable:-

1500 cfu/cubic meter MAX
1000 cfu/cubic meter MAX
2. Surface Microbiological Sampling

This is carried out by swabbing the surfaces with a sterilised swab, so that bacteria and fungi are imprinted onto the swab, the individual counts for each location are converted to counts per 10 square centimetres.

Colony Forming Units (cfu per 10cm²)
Less than 10
Greater than 10 but less than 20
Greater than 20
3. Harmful Gas Sampling

This is carried out by drawing a pre-determined volume of air through colour change detector tubes Occupational Exposure Standards or Maximum Exposure Limits are assigned. These levels of exposure are relative to an industrial workplace and are intended to protect a normal population of healthy workers working normal shifts. For offices, accommodation and other non-industrial environments a background concentration of less than one tenth of the OES or MEL is normally accepted.

OES/MEL (8hour TWA)
Office Environment
Carbon Dioxide
5000 ppm OES
500 ppm max
Carbon Monoxide
50 ppm OES
5 ppm max
2.0 ppm MEL
0.2 ppm max
0.10 ppm MEL
0.01 ppm max
4. Comfort Conditions

These are normally measured using appropriate direct reading electronic instruments as hand-held or as static arrangements to determine if conditions are within comfortable ranges. Thermal comfort is dependent upon a number of factors which can vary between different people carrying out different jobs in the same building. A normal population of people has a wide range of what is perceived as comfortable conditions. For normal office activity, conditions approximating to the following will normally be near to acceptable for most people:-

Approximate Comfort Parameters
Air Temperature
20°C - 23°C
Relative Humidity
40% - 70%
Air Velocity
0.1 - 0.2 m/s

One of the major purposes of heating, ventilation and air conditioning (HVAC) systems is to supply air to the occupied areas of a building in what is generally accepted as the most comfortable range of temperature for the majority, that is at least 80%, of the building users. This “acceptable” range will vary depending on the use and location of the specific building but for most practical purposes the ranges recommended by CIBSE for office and similar buildings should be suitable.

5. Airborne Particle Counts

This is measured by passing a pre-determined volume of air through a light beam and using scintillation to measure particle count and particle size. Counts are normally given for a range of particle sizes.

Particle counts can be used to compare air cleanliness in different parts of a building or with fresh and recycled air. In certain situations they can be compared to BS 5295. (Environmental Cleanliness in Enclosed Spaces).

Related Information

Surveys are carried out to the clients specification and prices for the works are dependent on the number of tests carried out and the size of the building. A comprehensive IAQ report is issued following the testing which contains the sampling results and gives a more detailed explanation of the areas covered by the survey.

The report can be posted on Health & Safety notice boards and gives a clear indication of monitoring of air in the working environment, to the benefit of employees. This has been proven to increase productivity of staff whilst reducing absenteeism in the workplace.