Indoor Air Quality in Office Buildings: A Technical Guide

5.2.7 Volatile Organic Compounds

The term "organic compounds" covers all chemicals containing carbon and hydrogen. Volatile organic compounds are those organic compounds that have boiling points roughly in the range of 50-250^oC. There are probably several thousand chemicals, synthetic and natural, that can be called VOCs. Of these, over 900 have been identified in indoor air, with over 250 recorded at concentrations higher than 1 ppb. Some of the most commonly encountered ones and their sources are listed in Table 3.

Outdoor levels of VOCs should be low (0.1 mg/m³ or less) if there are no sources. Indoor levels may be substantially higher. Typical office levels range from a few micrograms to a few milligrams per cubic metre. All buildings contain a large variety of chemical sources, such as plastics, cigarette smoke, floor wax, cleaning compounds and substances associated with combustion, liquid-process printers, or copiers.

Identification and measurement of individual VOCs are expensive and time-consuming, and invariably the total is underestimated because the VOCs present at very low concentrations are difficult to identify or measure. The concept of total VOCs (TVOC) was developed to deal with this situation. Measurements of TVOC record total VOCs present without distinguishing different chemicals.

5.2.7.1 Standards

The threshold limit values (TLVs) for individual chemical substances that have been adopted by the ACGIH are not appropriate for office environments, for several reasons. For example, ACGIH TLVs apply to industrial workers who may be exposed to a few known contaminants at high concentrations over a 40-hour work week. Industrial workers are usually provided with adequate protective equipment (e.g., source ventilation, protective clothing or face masks, breathing equipment). In addition, the industrial workforce is generally made up of young, healthy, adult males.

Office workers, on the other hand, are exposed, without protective equipment, to a broad spectrum of contaminants at low concentrations over periods often longer than 40 hours per week. The synergistic effect of these compounds on occupant comfort is not known. As well, the population composition of the office workforce covers a much broader spectrum than that of the industrial workforce.

It would therefore seem that individual limits much lower than ACGIH TLVs are more appropriate. ASHRAE Standard 62-1989 recommends using one tenth of ACGIH limits for compounds for which comfort guidelines do not exist. Although there are at present no Canadian or U.S. standards for TVOC, target and action units of 1 and 5 mg/m³ respectively, are being discussed. The European Community has prepared a target guideline value for TVOC of 0.3 mg/m³, where no individual VOC should exceed 10% of the TVOC concentration.

5.2.7.2 Health and Comfort Effects. Research in Europe and North America has demonstrated that VOCs at concentrations much lower than the ACGIH TLVs can cause discomfort. Symptoms of low TVOC exposure include fatigue, headaches, drowsiness, dizziness, weakness, joint pains, peripheral numbness or tingling, euphoria, tightness in the chest, unsteadiness, blurred vision, and skin and eye irritation.

In an exposure range of 0.3-3 mg/m³, odours, irritation, and discomfort may appear in response to the presence of TVOC together with thermal comfort factors and stressors. Above about 3 mg/m³, one may expect complaints; above 25 mg/m³, temporary discomfort and respiratory irritation have been demonstrated for a common mix of chemicals in an office building. Typical office levels cover a range from below to above the amounts found to cause discomfort.

Hypersensitive individuals can have severe reactions to a variety of VOCs at very low concentrations. They can react to organic compounds that are released by building materials, carpets, and various consumer

products, including cosmetics, soaps, perfumes, tobacco, plastics, and dyes. These reactions can occur following exposure to a single sensitizing dose or sequence of doses, after which time a much lower dose can provoke symptoms. Chronic exposure to low doses can also cause reactions. Symptoms are usually non-specific and may be insufficient to permit identification of the offending compounds.

Because the available knowledge of toxicological and sensory effects of VOCs and their mixtures is incomplete, reduction of overall exposure to VOCs is desirable.

5.2.7.3 Checklist

Inspections should be carried out in complaint areas and in locations that are potential sources of VOCs, such as local printshops, photographic darkrooms, laboratories, and chemical storage areas.

The following questions should be asked:

• Is the building less than a year old, or has any area been renovated, redecorated or newly furnished within the past month?
• Are suitable cleaning products being employed? Is time of use optimum, so as to reduce exposure of occupants?
• Do any activities involve the use of large amounts of chemicals, especially highly volatile solvents? Are solvent odours present? Are soaked materials and solvents being disposed of properly?
• Is extra ventilation or a separate ventilation system being used where there are localized sources? Is the ventilation system recirculating VOCs from a source throughout the building?

5.2.7.4 Measurement Methods and Equipment

Suitable control and test locations are identified from results of the preliminary assessment. The assumptions and analytical methods used should be clearly stated when reporting VOC results.

a. Direct-reading tubes

Direct-reading tubes contain chemicals that react with certain individual VOCs to produce a colour change. A fixed volume of air is drawn through the tube by means of a hand pump. The length of stain observed is proportional to the volume of air sampled and the concentration of VOCs. The method was developed for the industrial environment and is only marginally suitable for use in the office environment because of the much lower VOC concentrations usually found there. The method may, however, be useful for screening purposes. Sensitivities are in the parts per million range.

b. Passive badges

Passive organic vapour samplers are available with sensitivity levels in the range of sub-parts per million. These samplers employ charcoal or another medium as an adsorbent and use sampling periods of 8 hours to 1 week. The sampler is sent to a laboratory for analysis and provides average concentration.

c. Photoionization detectors

Photoionization detectors (PIDs) are direct-reading instruments that detect airborne chemicals by first breaking them into electrically charged fragments by means of an ultraviolet (UV) lamp, then detecting the fragments (ions) on a metal screen. The number of VOCs that can be detected increases as the lamp’s UV energy increases: 11.7 electron volt is the highest energy commonly available and the most suitable for offices. Note that identification of the individual chemicals present is not possible.

Responses have been measured for a number of chemicals commonly found in office air. As they vary quite widely, detector accuracy is probably no better than 50% when measuring TVOC. Toluene is recommended for use as the calibration gas, as it has an intermediate response.

PIDs are very useful screening devices and can identify source locations and pollution migration routes.

d. Flame ionization detectors

In the flame ionization detector (FID) method of measuring TVOC, chemicals in air are burned to produce ionized products that generate a current in proportion to the concentration. The ionization process is non-specific, and the result is displayed in real time.

Like PIDs, FIDs are useful for qualitative survey work, such as source location during a walkthrough and the identification of sampling points. The variability in response is much less for the FID than for the PID. Also, a greater number of VOCs are detected by the FID method.

Several instruments combine a FID for screening with a portable gas chromatography (GC) unit for more detailed analysis and specific compound quantitation.

e. Infrared detectors

Infrared detectors are direct-reading instruments suitable for monitoring individual VOCs. The variable-wavelength models can be adjusted to scan for several different VOCs.

The sensitivity is in the parts per million and sub-parts per million range but is not as good as that of a GC, and there can be a problem with interferences when several VOCs are present together.

Direct-reading instruments such as PID, FID, and infrared detectors can be operated over several hours or several days with chart recorders and external or internal data loggers to yield concentration profiles over time.

f. Active sorption/chemical analysis

Active sorption methods employ tubes packed with a sorbent that traps the VOCs when air is pumped through the tubes. Sorbents include organic polymer resins, such as Tenax, XAD, or activated charcoal. The analysis yields information on the type and quantity of chemicals present.

In charcoal tube sampling with solvent extraction, charcoal tubes are used with battery-operated sampling pumps, and the VOCs collected are extracted with solvent, usually carbon disulphide. Either GC or GC with mass spectrometry (MS) is used for the analysis. The GC/MS gives more detailed information for identification of chemicals present.

Charcoal tubes demonstrate nearly 100% accuracy in detecting non-polar hydrocarbon and chlorinated hydrocarbon solvents with boiling points in the range of 50-200^oC. However, some chemicals (those that tend to dissolve in water rather than in solvent, such as ammonia and darkroom chemicals) are not well trapped or extracted and are detected with low efficiency. An additional problem with this method is that VOCs are measured individually, so one must total the individual measurements to calculate TVOC. Where complex mixtures of chemicals are present (e.g., liquid-process photocopier solvent), this method underestimates TVOC, because many of the chemicals are present in quantities too small to be measured.

Multi-sorbent sampling with thermal desorption seeks to improve on the charcoal tube method in three ways:

• Using tubes containing three adsorbents extends the trapping range of the tubes to a wider boiling point range.
• Thermal desorption is used to transfer the VOCs from the tube to a GC or a GC/MS. This increases the number of VOCs detected, because only chemicals in the charcoal tube that dissolve in the solvent during solvent extraction will be transferred.
• The sample is split, and part goes directly to a FID that detects all the chemicals in the sample regardless of the type and quantity present. This gives a better measure of TVOC than the charcoal tube method. The remainder of the sample is analysed by a GC or GC/MS in the usual way to provide identification.
  

A variety of other adsorbent tubes exists, using both solvent extraction and thermal desorption. For example, there are tubes specifically prepared for collecting dioxins or polychlorinated biphenyls (PCBs). It is also possible to measure individual chemical concentrations using thermal desorption.

5.2.7.5 Strategy for Remediation

Measures to control VOC emissions include selection of materials with low emission rates, and increased ventilation during the first 3 months of occupancy in new or retrofitted buildings.

Chemical emissions occurring as a result of occupant or maintenance activities should be counteracted. Courses of action include:

• increasing outside air levels to dilute concentrations if the source is weak (e.g., emissions from new furnishings)
• storing paints, cleaners, and solvents in areas with separate exhaust and not in the mechanical room
• choosing dry process copiers over wet copiers if many copiers are used in the building
• installing local exhaust for print machines and photographic dark-rooms.