Indoor Air Quality in Office Buildings: A Technical Guide

5. Detailed Assessment

During a detailed assessment of an indoor environment, air quality indicators and pollutant sources are investigated and measured and the HVAC system is checked. Tools include checklists and calibrated measuring equipment.

Some measurements may require the use of complex instruments and laboratory analysis. Specialists may be required at certain stages of the diagnostic process, and a team approach is advisable. An industrial hygienist, chemist, or engineer may be able to measure and evaluate a variety of suspected pollutants, whereas a mechanical engineer can evaluate the effectiveness of the design and operation of the ventilation system. Because most office buildings rely on the HVAC system to provide contaminant control by ventilation, it is important to understand the performance of the system.

5.1 Collecting Information about Air Quality Indicators

Before discussing the individual pollutant sources, we will examine the factors that should be considered when making a measurement, the equipment and methods employed, and the investigative procedures.

5.1.1 Purpose of Measurements

Air sampling should not be undertaken until some or all of the other investigative methods available have been exhausted. The sampling strategy should be based on a comprehensive understanding of how the building operates and the nature of the complaints.

Air sampling of the various indoor contaminants is needed to address the problem of SBS. High readings may be considered conclusive evidence of a problem. However, low readings do not necessarily preclude the existence of subtle or intermittent air quality problems.

It may be desirable to take certain preliminary air quality measurements that are indicative of common IAQ concerns, such as temperature, relative humidity, air movement, and carbon dioxide.

Air sampling makes it possible to:

• establish baseline conditions so that levels measured in problem areas can be compared with concentrations at other times and at other locations
• compare indoor with outdoor air quality
• test a hypothesis about the source of the problem
• confirm that a control approach has the desired effect of reducing pollutant concentrations or improving ventilation
• reveal the existence of compounds associated with particular types of building problems (e.g., a carbon dioxide reading over 1000 ppm is an indicator of underventilation; a carbon monoxide reading over 5 ppm is an indicator of unvented combustion products or vehicle exhaust entrainment)
• compare measured concentrations with occupational exposure standards and with public health and comfort guidelines for specific pollutants.

5.1.2 Sampling Considerations

There are several ways to locate sampling sites for an IAQ investigation. A building may be divided:

• by individual HVAC zones
• by types of HVAC zones (interior vs. perimeter)
• by complaint vs. non-complaint areas
• by relationship to major sources (e.g., proximity to smoking areas, printing shop)
• by complaint types.

It is best to measure pollutants arising from the building structure, furnishings, or ventilation (e.g., formaldehyde, VOCs, microbial contamination) in the morning if the ventilation system is turned off overnight or over the weekend. Pollutants generated by the occupants (e.g., carbon dioxide) or by the occupants' activities (e.g., use of photocopiers) are best checked toward the end of the working day in order to detect the highest concentration.

The time of year is also an important consideration. If the building is on an economizer cycle, outdoor air supply will be less during very cold or very hot weather, which generally makes pollutant concentrations higher. Also, some sources are seasonal, emanating from humidifiers and air conditioning systems.

Proper operation of IAQ measuring equipment and proper calibration are critical to the success of any sampling program. Calibration to ensure accurate measurements is usually done using a known standard on the low (zero) and high (span) range of the expected measurement.

Sampling strategy should be designed to assess worst-case conditions, such as instances of maximum equipment emissions, minimum ventilation, or disturbance of contaminated surfaces. Worst-case sampling results can be very helpful in characterizing maximum occupant exposure.

Sampling time can vary in length according to the lower detection limit of the analytical method, the emission characteristics of the source, the degree to which pollutant concentrations vary, and any specific objectives of the measurement.

Experience has shown that the vast majority of chemical pollutants will be present at concentrations far below those known to cause health-related problems. Although the capability of these substances to cause discomfort in trace concentrations, alone or as part of a mixture, is not well understood, it is clear that the use of traditional industrial hygiene standards and criteria does not provide a meaningful basis for the evaluation and subsequent resolution of IAQ complaints.

5.1.3 Overview of Monitoring Methods and Equipment

Simple measurement methods are available for the non-specialist, such as the building operator or property manager who has received complaints about air quality in a building. These measurements are easy and quick to perform.

Failure to detect IAQ problems through measurement of individual parameters does not mean that no problem exists. Chances are that an irrelevant parameter was measured, the measurement was taken at an inappropriate time, or existing permissible exposure standards are simply not adequate to determine if one air contaminant or a combination of contaminants constitutes a comfort risk for some people.

Measurement effectiveness can vary according to whether the method is passive or active, whether the instrument is a sampler, analyser, or direct-reading device, and whether measurements are continuous or grab (spot). Passive samplers such as badges are inexpensive and simple to deploy; however, they usually require laboratory analysis to

determine the contaminant level. An active sampler, such as the colorimetric sampling tube, is also inexpensive and will provide on-site spot measurements for carbon monoxide, carbon dioxide, and other specific pollutants. However, it has limited sensitivity.

Direct-reading instruments can be employed for spot checks or can be set up for continuous monitoring of specific pollutants. However, they are expensive and equire calibration and some operator training.