Indoor Air Quality in Office Buildings: A Technical Guide

5.2.6 Particulates

Particulates are solid or liquid matter with aerodynamic diameters ranging from 0.005 to 100 mm. Dusts, fumes, smoke, and organisms such as viruses, pollen grains, bacteria, and fungal spores are solid particulate matter, whereas mists and fog are liquid particulate matter. Indoor particles come from both indoor and outdoor sources and can be drawn into the building via infiltration and outdoor air intakes. The mechanical ventilation system itself may be a source of particulates (e.g., humidifier additives, scale, rust, disinfectants, biological growth, duct and pipe insulation).

Fibres, synthetic or natural, are also classified as particulates. Asbestos fibres are not included in this report, as they are covered comprehensively in other publications. Product information sheets on respirable glass wool fibres bear the following caution: "Based on studies of laboratory animals, fibre glass wool has been classified as a possible cause of cancer." Although no comfort standards currently exist for respirable glass fibres, it would seem prudent to minimize exposure through safe work practices. Work areas being renovated should be sealed off, and damaged ceiling tiles, pipe insulation, sound barriers, etc., should be replaced or repaired.

The size range of concern to human health and IAQ is 0.1-10 mm. Particles smaller than 0.1 mm are generally exhaled, and most particles above 10 mm will be filtered by the nose. Particulates are classified as total suspended particulates (TSP) or respirable suspended particulates (RSP), which consists of those with particle size under 10 mm. Small particles that reach the thoracic or lower regions of the respiratory tract are responsible for most of the adverse health effects, and guidelines have been developed for those particles 10 mm or smaller (PM ₁₀). ASHRAE Standard 62-1989 has adopted the U.S. Environmental Protection Agency PM ₁₀ standard of 50 mg/m3 for annual exposure and 150 mg/m3 for 24-hour exposure.

In office buildings, the average particulate concentration found in a non-smoking environment is 10 mg/m3. In smoking areas, it can range from 30 to 100 mg/m3.

Excessive levels of particulates can cause allergic reactions, such as dry eyes, contact lens problems, nose, throat, and skin irritation, coughing, sneezing, and respiratory difficulties. The effects of exposure to tobacco smoke particulates range from headaches and short-term irritation of the eyes, nose, and throat to aggravating the conditions of people with pre-existing diseases - including respiratory and heart disease, allergies to other substances, and cancer.

5.2.6.1 Checklist

Inspections should be carried out in areas that have been recently renovated, in areas where there have been complaints, and in the mechanical equipment room. The following questions should be asked when assessing the likelihood of particulate contamination:

• Are materials coming into the building through the air intake?
• Are the outside air dampers screened, and is the entry free of debris and dirt? Is there dust on surfaces?
• Is the filtering system designed for primary filters, rated between 10% and 30% dust-spot efficiency, and for secondary filters, rated between 40% and 85% dust-spot efficiency?
  Are filters installed and maintained properly?
• Are particulates entering the air from the humidification equipment (spray or ultrasonic humidifiers, chemical disinfectants, corrosion, rust)?
• Are there chalky marks or cement-like odours around the humidifier?
• Are there personal ultrasonic humidifiers in the workplace?
• Is there evidence of damaged insulation in the ducts or AHUs?
• Are there dirt marks or white dust on diffusers, indicating particulates entering from the ventilation system?
• Is smoking taking place anywhere in the building?
• Are large amounts of paper being stored or moved, or are there paper-shredding activities?
  

5.2.6.2 Measurement Methods and Equipment

Weight by volume of sampled air or particle count is measured. The exposure standard is by weight.

a. Gravimetric method

In the gravimetric method, a portable sampling pump is used to draw a measured volume of air through a filter enclosed in a cassette. Collected materials are deposited on the filter. The difference in the weight of the dried filter before and after sampling corresponds to the mass of particulates. Matched-weight filters are available to correct for humidity changes in the filter during and after sampling and to eliminate the need for weighing the filter before sampling.

The procedure uses a 37-mm filter and a calibrated pump capable of at least 8 hours of sampling at 2 L/min. The particulates can be further examined under a microscope to determine whether particles or fibres are present.

To separate particulates into size fractions, usually less than 10 mm, a nylon cyclone can be used. Another method uses a series of size-selective plates, or a cascade impactor, collecting particles at each stage on filters.

Filtration methods are the simplest and lowest-cost methods available; however, a precise balance and stringent quality control procedures are required. A large air volume must be sampled to obtain accurate measurements, which have a detection limit of 5 mg/m3.

b. Optical scattering

In the optical scattering method, air passes through a size-selective inlet to an optical cell, where the presence of the particulates results in light scattering. The amount of scattering is related to the number of particles. Depending on the instrument and the length of the sampling period, levels of 0.001-200 mg/m3 can be measured. Measurements are indirectly related to mass concentrations, as a factor is used to convert particulate number to weight. Some instruments provide particule counts and concentration by size range and are ideal for outdoor/indoor and site comparison.

These instruments provide immediate results and can be used by personnel without specialized training, which makes them a popular choice for surveys and walkthroughs.

c. Piezoelectric resonance

Piezoelectric monitors pass air through a size-selective inlet, and particles are electrostatically precipitated onto a quartz crystal sensor. The collected particles change the oscillation frequency of the crystal, and these changes are related to the collected particle mass. These instruments have a measurement range of 0.005-20 mg/m3 and can be used by operators with little training.

Piezoelectric monitors can obtain true mass concentrations in real time. They do not provide samples for later analysis. They can be used with data loggers for continuous measurements.

5.2.6.3 Strategy for Remediation

Methods of reducing particulate levels are:

• controlling, exhausting, sealing, or relocating the source
• upgrading the filtering system
• increasing the outdoor airflow
• avoiding recirculation of air that contains contaminants.

High levels of particulates due to smoking are ideally controlled by banning smoking or, alternatively, by isolating the activity in a specially designed room maintained at negative pressure, with a dedicated exhaust.