Measuring Air Quality

Respiratory Protective Equipment (RPE)

One of the most valuable services that we offer in this area is a comprehensive assessment of the way in which RPE is selected, used and maintained. The current COSHH code of practice states that a thorough examination and where appropriate, testing of RPE should take place at least once a month and more frequently where conditions are particularly severe. The inspection, maintenance and testing of RPE should be carried out by trained personnel and a proper records of these activities should be kept.

The use of appropriate RPE is especially important when two-pack polyurethane coatings and other potential respiratory allergens are used

We can measure the quality of air supplied to air-fed masks and helmets using colorimetric detector tubes. Substances monitored include water vapour, carbon monoxide, carbon dioxide and oil mist.

Spray Booths

During paint spraying operations the whole paint is transformed to a mixture of VOC’s and particles and consequently is potentially both respirable and ingestible. If the coating contains flammable solvents, there is also a risk that the mixture of vapour and particles will exceed the lower explosive limit (LEL).

We can carry out a number of checks on spray booths. A smoke test will reveal any regions within the booth where air is either stagnant of recirculating. We would then use an explosimeter to measure the flammable vapour concentration in these regions in order to check that it was less than 25% of the LEL. We would also measure the extract face velocity using a rotating vane anemometer and compare this value with the minimum recommended value given in the HSE guidance document HS (G) 54 “Maintenance, examination and testing of local exhaust ventilation” (1998).

From a knowledge of the extraction rates together with the paint and the spraying conditions used, we are able to estimate the potential VOC, particulate and (where appropriate) the isocyanate concentrations.

Spray Guns

When a paint is spray-applied, all the VOC’s and a proportion of the particles leaving the gun are destined to become air pollutants. A well designed and correctly operated spray gun will produce a minimum amount of paint overspray.

We can measure how efficient spray guns are at transferring paint to the object being coated ( as opposed to transferring it to the atmosphere or to surrounding structures). We follow the general principles of ASTM D5286-95 “Determination of transfer efficiency under general production conditions for spray application of paint”.

The test is normally carried out using a paint and a spray booth which are representative of the client’s normal production process. Metal test panels are weighed before and after paint is spray-applied. The weight of the paint leaving the nozzle of the gun is measured and the non-volatile content of the paint is determined. Using these values it is then possible to calculate the weight of the paint on the test panels as a percentage of the weight of paint that was discharged from the gun. This value is the spray gun transfer efficiency. A minimum value of 65% is recommended in the Process Guidance Notes PG 6/23 “Coating of metal and plastics” (1997) and PG 6/34 “Respraying of road vehicles” (1997).

Consultancy Services

In addition to measuring air quality and equipment efficiency, we will be pleased to advise on the most efficient and cost effective methods of complying with the appropriate legislation and guidelines. In particular our consultant can tell you about the advantages and limitations of:-

  • changing the operational procedures
  • using alternative materials
  • installing or modifying ventilation equipment

We are very experienced with working for small companies where money is simply not available for re-equipping the factory or installing state of the art ventilation equipment. We can usually suggest a practical, low-cost solution that will enable you to maintain production and work within current emission limits.

Measuring Air Quality

We can measure the concentration of air pollutants in the general working atmosphere and in the breathing zone of selected operators:-

Volatile Organic Compounds (VOC’s)

We can carry out these measurements at static points or within the breathing zone of operators. Depending on the circumstances, we collect samples using either an adsorption tube-pump combination or diffusive tubes.

The absorption tube method is carried out in accordance with MDHS 96 “Volatile organic compounds in air (4)” (2000) while the diffusive tube method follows the basic principles of MDHS 80 “Volatile organic compounds in air” (1995). In either case the tubes are returned to a UKAS accredited laboratory where they are desorbed and the volatiles identified and quantified using gas chromatography.


We can collect total or respirable particulates using static or breathing zone sampling techniques. Both methods involve the use of a pump-filter combination with the filter being weighed to determine the amount of particles collected from a measured volume of air. In the case of respirable particulate determination, a cyclone device is used to prevent non-respirable sized particles reaching the filter.

All particulate determinations are carried out using the principles for personal sampling given in MDHS 14/3 “General methods for the gravimetric determination of respirable and total dust” (2000).


Isocyanate concentrations are measured in accordance with MDHS 25/3 “Organic isocyanates in air” (1999). This involves drawing a measured volume of air through a filter impregnated with 1-(2-methoxyphenyl) piperazine reagent. The filter is then returned to a UKAS accredited laboratory where the concentration of free isocyanate groups is determined using high performance liquid chromatography (HPLC).

 Measuring Equipment Efficiency

It is vital that ventilation and respiratory protection equipment used in the workplace is fit for the purpose, correctly operated and properly maintained. Our tests are designed to address all of these points.