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Indoor Air Quality

Nov 14, 2018

EBS Ltd was asked to investigate complaints of ill health and reduced productivity of staff, linked to suspected poor air quality in a large local authority building.


The building was made up of six levels including a basement.  This is a modern building with open plan administration units fitted with passive multiservice chilled beams based in the heart of City Centre. Over 2000 members of staff worked on different floors in open plan working stations.

A group of staff reported specific health concerns and similar symptoms in certain areas. The symptoms being claimed by the affected employees were; 

  • Bouts of coughing
  • Chest tightness
  • Wheezing
  • Breathlessness 

 Additional symptoms experienced by staff working in specific areas were headaches, fatigue and ailments such as itchy eyes.

Prior to EBS Ltd’s involvement, two previous indoor air quality  Investigations had been undertaken and no abnormal conditions had been found.



EBS Ltd investigation


EBS Ltd performed a preliminary investigation, concentrating on the first floor of the property in June. During this process we looked at the following;


  • Mycoflora and Environment - To determine airborne, surface and hidden particulate contamination by moulds and biological matter in the indoor environment.
  • Ambient and Air Extraction Locations - Monitoring for mould Colony forming units (CFU) per cubic meter at floor level, breathing zone level and ceiling level.
  • House Dust Mite Analysis - Monitoring and analysis for house dust mite.
  • Air Movement - Measurements of air movement were taken at various positions throughout the first floor.
  • Temperature and Humidity - Temperature and relative humidity were recorded simultaneously at various locations throughout the first floor.
  • Formaldehyde - Sampling for formaldehyde vapours at various locations.  
  • Tests for ozone emissions from copier and other electronic equipment in office areas - Monitoring for ozone was carried out in areas where equipment such as printers were situated 
  • Airborne Dust Monitoring - Respiration/total inhalable dust, collection and analysis of dust samples.
  • CO2Monitoring - Carbon dioxide and temperature monitoring sensors were used for ventilation testing.  Data Loggers were used to store and record data from the CO2monitors. 


Continuous Environmental Monitoring

Continuous environmental monitoring was carried out using HOBO data loggers and these were set to monitor every ten minutes. The data loggers monitored temperature and relative humidity in three locations on the first floor.


Contact Mould Sampling

Contact sampling for mould infestation was undertaken by the readymade malt extract strip lift method and mould analysis was carried out to species level because it is vital to know if the species found in the monitored locations are pathogenic or toxic.


Pump Sampling Location


Sampling for viable and non-viable Moulds

Monitoring for viable and non-viable moulds was undertaken on the first floor.


Airborne Contaminant & Atmospheric Gases

Monitoring for airborne contaminant gases was carried out using environmental sensor technology. 




Mycoflora Monitoring

The results of mycoflora monitoring (colony forming units per cubic meter) revealed that the concentration of moulds in the monitored areas of the indoor environment on the first floor was low when judged on the scale proposed by theWorld Health Organisation (WHO).


House Dust Mite Analysis

Active house dust mite infestation was detected in the first floor.

This was mainly due to a build up of dust and organic matter on the floors. House dust mite (Dematophagoides pteronyssinus) lives in dust, which accumulates in unventilated voids and cavities, carpets, fabrics and furniture. 

Exposure to the faecal pellets of house dust mites can trigger a variety of true allergic reactions in susceptible individuals.  The allergens of house dust mite are Derp I, cysteine proteases, serine proteases and amylase. All these allergenic enzymes have been found in extracts of mite faecal pellets.

The results of the house dust mite analysis indicated low-level active infestation of house dust mite.

   Dust Mite Monitoring


Airborne Dust Monitoring

Airborne dust concentrations were well within accepted limits for occupational exposure to nuisance dust and in themselves appeared unlikely to be related to ill health amongst the occupants.


Airborne Contaminant Gases

The absence of inorganic pollutant gases had been confirmed at the time of the monitoring exercise. 


Airborne Atmospheric Gases

The levels of oxygen within the environment were entirely consistent with typical atmospheric concentrations.  Toxic gases were not detected at any time during the monitoring exercise. 


Air Movement

Air movement in a workplace is recommended by HSE to be between 0.1 and 0.15 metres/second and up to 0.25 m/s in summer. 

The monitoring carried out showed that air movement was generally below these limits.  The only area that was within these limits was below the ventilation grilles.


Air Movement Testing


Ozone Monitoring 

The results of this exercise have shown that ozone gas was not present at levels above the instrument’s detection limit.  


Monitoring Gasses



The carbon dioxide concentration levels normally observed in indoor environments range from 350 to 1772 ppm and are typically between 500 and 1,300 ppm.

However it has been demonstrated that levels above 1000 ppm tend to result in health complaints and a general guideline is that levels should be below 800 ppm to ensure everyone's comfort. However the levels observed was well within acceptable limits.

CO2levels above 1000 ppm correlate with complaints of minor health problems such as eye and throat irritation, headache and fatigue.  It is unlikely that CO2is causing these problems, more likely, CO2levels are high due to poor ventilation in the building and the cocktail of all the pollutants trapped at the same time as carbon dioxide building up. CO2levels above 5000 ppm are considered an occupational health risk and can cause drowsiness and other problems.

As the primary cause of high indoor COis the respiration of the occupants, reducing the level can only be achieved by increasing the air exchange rate.

   CO2 Sampling


Formaldehyde Sampling

Sampling for formaldehyde vapours showed that levels were all well within WHO guideline levels and therefore unlikely to be related to the ill health issues in the buildings.



The environmental conditions in the monitored areas at the time of EBS Ltd’s monitoring period ranged from of 25.1°C to 28.1°C, i.e. high temperatures. 

All the logger locations monitored high temperatures above the recommended guidelines, this was mainly due to exceptional summer weather.


Relative Humidity

The environmental conditions at the time of our monitoring period in the monitored areas e.g. relative humidity ranged from 23.4% to 48.1%.

The average relative humidity recorded ranged between 24% to 34%.

It was noted that although it is not ideal, RH values of 40% or below are not uncommon in heated only buildings, particularly when there are periods of cold weather. 

Furthermore, RH levels of 30% and below are acceptable for short periods of time if precautions are taken to limit dust and other airborne irritants. 

All the logging locations gave readings below 30% (23.4% to 26%) during the  two weekmonitoring period.




The detailed indoor air quality testing, monitoring was undertaken in the first floor only. A range of testing and monitoring works were undertaken over a period of two weeks and the majority of the factors tested were within acceptable limits.

However physical environmental condition monitoring indicated; 

  • That the relative humidity was very low 
  • Temperatures were high 
  • Air movement and ventilation was poor
  • CO within recommended guidelines but not ideal
  • The staff also lacked control to improve these conditions 


These conditions correlate with complaints of minor health problems such as eye and throat irritation, headache, fatigue and lower staff morale. 

Efforts should be made to improve the physical environment including ventilation and air movement.

In addition, active house dust mite infestation was found, which reflects inadequate cleaning practices.

We recommended that in order to gain a meaningful holistic view of the air quality, health, comfort and productivity, it would be necessary to investigate the whole building. 




House Dust Mite Hygiene

It was recommended to thoroughly and regularly vacuum floors with HEPA filter vacuum and ensure that these are free of dust.  Regularly vacuum the floors and crevices around carpets. 


Environmental Conditions

When the RH is significantly low for long periods the skin and mucous membranes of the nose and throat dry out, dry skin becomes itchy and scratching can lead to dermatitis.  Dry mucous membranes mean a greater susceptibility to infection.

It was recommended to limit the negative effects of high and low RH levels, a range between 40% and 65% should be maintained.  

Efforts should be made to maintain temperatures below 24°C if possible.


Ventilation & Air Movement

The monitoring carried out showed that air movement was generally below what is recommended in workplaces.  

It has been demonstrated that CO2 levels above 1000 ppm tend to result in health complaints and a general guideline is that levels should be below 800 ppm to ensure everyone's comfort.

Efforts should be made to improve ventilation and air movement, and increase the number of air changes per hour.


Mycoflora Monitoring

The purpose of this exercise is to determine the counts of moulds in the indoor environment, so that appropriate recommendations can then be put in place if necessary.

On going long term environmental monitoring to monitor the indoor environment throughout the building and over different seasons throughout the year, will help to assess the quality of the indoor environment.  If the various contributory factors are found to be below the comfort range, then appropriate recommendations should be put in place.

This pilot investigation provides information on the concentration of fungi, which can be encountered in the indoor environment. The databases on the distribution of the levels, in conjunction with occupants’ response, must be large enough to provide useful information for this assessment and management. 

It was therefore recommended that a systematic Mycoflora assessment be undertaken, so that appropriate recommendations can be provided.


Airborne Dust

The concentrations of airborne dust measured were all within acceptable limits and although the nature of the dust was not studied, it was concluded that, other than for particularly sensitive individuals, the atmosphere within the building was satisfactory for occupation.  


Remedial Chemical Treatments 

No remedial chemical treatments, such as spraying with chemicals for infestation control were recommended.


Duct Work Hygiene

We recommended a systematic inspection of the ductwork hygiene throughout the building and to take representative samples to assess levels of contamination.  To then carry out ductwork cleaning as appropriate.


Further Investigation


Continuous CO2Monitoring

It was recommended to carry out continuous CO2monitoring in the building over a period of one month in existing and other areas of the building, so that appropriate analysis and recommendations could be made.

   CO2 Sampling


Continuous Environmental Monitoring

It was recommended to carry out continuous environmental monitoring over a period in existing and other areas of the building, to monitor the conditions over different seasons.

On going long term environmental monitoring of parameters such as temperature and RH should be monitored over different seasons throughout the year.  This will help to further assess the environment, check the efficacy of the remedial works carried out to date and to provide information to calculate additional environmental changes.

On going environmental monitoring should also be undertaken as a check that the intended environmental conditions are being achieved and provide a platform to monitor for any adverse effects.


Environmental Conditions Monitoring 


Mycoflora Monitoring, Contact Sampling, Viable and Non-viable Mould Monitoring 

We recommended that a systematic Mycoflora assessment be undertaken throughout the buildingin various locations, including cavities and voids to get a meaningful picture, so that appropriate proposals could be provided.

Contact mould sampling for mould infestation would need to be undertaken throughout the building.  Mould analysis carried out to species level, as it is vital to know if the species found in the building are pathogenic or toxic.


Examination of Ventilation System 

It was considered that the ventilation system might have some involvement in the health issues amongst some staff.  Therefore it was recommended that the operation of the system, including the intake of appropriate quantities of fresh air, be verified.

It was also recommended that the internal condition and cleanliness of the various components of the ventilation system be investigated.  This would entail visual examination and sampling from internal surfaces.

Samples should be subsequently analysed for both chemical and microbiological contamination.  As part of this study it was also recommended that measurement of the actual ventilation conditions be made to establish whether sufficient fresh air was being supplied to the building.  


HVAC System and Moulds

In a large building with HVAC system, the common source of moulds is from dirty filters, accumulated debris in ducts, humidifiers subject to condensation and leaks and contaminated ductwork. 

This aspect of the HVAC system needs to be independently and systematically investigated. 

  Contact Mould Sampling



Mould Sampling Location


House Dust Mite and Mycoflora and Environmental Investigation

House dust mite, Mycoflora and spot environmental monitoring should be undertaken at six monthly intervals to check for seasonal changes in the indoor Mycoflora.


Formaldehyde Sampling

As Formaldehyde levels were all within acceptable levels, it was not considered to be an issue.  


VOC Formaldehyde Monitoring