I have been appointed out carry out an investigation into the air quality in an office building situated on a major UK airport. The occupants of the building were complaining from strong fuel related odours and were concerned about the efficiency of the air management system. My task was to evaluate the levels of volatile compounds such as kerosene and diesel in the ambient supply air and in the indoor air within the offices. I also investigated the general state of the air management units, supply ducts and air treatment elements for sighs of malfunction, deterioration or biological contamination.
To adequately evaluate the air quality in the office in direct relation to the supplied air it was necessary to collect the air samples in the air supply units and ducting before it enters the office areas. The reason for this approach was that the office occupant themselves introduce a variety of volatiles into the indoor environment. The occupant related volatiles would then introduce a complicating factor into the assessment. Because the objective of this indoor air quality investigation was to evaluate the air management system the inspection and sampling was limited to the system itself.
The air handling unit were located on the top floor of the building and facing the main aircraft parking zone. Because the aircraft were being refuelled while stationary in their parking position the building and subsequently the building occupants were likely to be affected by odours from aviation fuel and diesel for the maintenance and transport vehicles.
The aviation fuel consist of many chemical constituents but kerosene is a major component (> 60%) and consists of a mixture of n-Alkanes (~80%), Alkyl-monoaromatics (~13%), and mono-, di- and polynuclear aromatics and Naphthalenes (~7%). The reported odour threshold level for kerosene is approximately 0.5 mg/m3 but because the kerosene is a mixture of various chemical this can vary significantly.
Also there is not occupational exposure limit set for kerosene in the UK several US organisations have produced standards. The National Institute for Occupational Safety and Health (NIOSH) list 100 mg/m3, TWA 10hr, for kerosene in air. The American Conference of Governmental Industrial Hygienists (ACGIH) indicates a 200 mg/m3, 8hr and the US Department of Defence quotes 350 mg/m3 as acceptable workplace exposure level 8hr. Non-occupational levels for kerosene have also been established by The Agency for Toxic Substances and Diseases Registry (ATSDR) and set to 0.01mg/m3 for a minimum risk.
Diesel is a complex mixture of hydrocarbons chemicals mainly obtained from the distillation of crude oil. The reported odours threshold limit for diesel vapours is 0.7ppm. Similarly there is no UK occupational exposure limit set to diesel vapours but UK organisation state 100 mg/m3 8hr, as the maximum workplace exposure limit. UK has established a workplace exposure limit o general volatile organic compounds which varies depending on exact composition of the mixture. For this assessment I have decided to use the 500mg/m3 limit used for aromatic volatiles as both kerosene and diesel fumes contain aromatic volatiles.
As for the biological contamination there are no currently established limit on acceptable levels of bacterial or mould in air supply streams and therefore the assessment is base of comparative evaluation of pre-treated and treated air and also on the relative levels of mould and bacterial on the internal surfaces of the dusting.
In my assessment I have collected large number of biological samples from the internal surfaces of the air duct supply system to evaluate the levels of bacterial and mould contamination. The result of the sampling suggested that the air handling unis and associated ducting were from biological contamination. Visual inspection of the ducting confirmed that the air supply dust were cleaned and well maintained. Inspection of the associated areas however showed significant shortcoming in the overall maintenance of the premises. A large amount of pigeon faeces were detected in the plant room. The presence of pigeon faeces in the plant room by itself does not present a significant air stream contamination risk but is indicative of a lack of maintenance. In any case the due to the presence of pigeon dropping is the areas an immediate clean was strongly recommended.
In relation to chemical contamination of the supply air I have detected significant levels of volatiles in the fresh air supply. This was to be expected due to the building’s location and close proximity to refuelling station. To address the problem of odours in the internal areas the original air management design incorporated the use of carbon filters. My inspection identified that the carbon filters were missing from this unit allowing the fuel related odours pass unhindered through he air treatment units.
My measurement confirmed that levels of volatile in the fresh air supply and treated air supply were very similar.