Indoor Air Quality in Office Buildings: A Technical Guide

5. Detailed Assessment

5.2 Individual Source Evaluation

5.2.5 Formaldehyde

Formaldehyde is a colourless gas. A pungent odour often indicates its presence at a concentration greater than 0.2 ppm. Formaldehyde is present when vapours off-gas from building materials (e.g., carpets, particleboard, fabrics), cleaning fluids, and adhesives.

Indoor concentrations are dependent on the age of the source, ventilation rate, indoor and outdoor temperatures, and humidity. Formaldehyde concentrations can also vary by as much as 50% from day to day and from season to season.

The measured results can be compared with the various guidelines available; typical office levels should be under 0.1 ppm.

Formaldehyde is a known irritant and sensitizer. Symptoms include dry or sore throat, nosebleeds, headaches, fatigue, memory and concentration problems, nausea, dizziness, breathlessness, and burning, stinging, and pain in the eyes. Irritant effects have been associated with concentrations in the median range of 0.5 ppm, and concentrations as low as 0.01 ppm have been reported to affect sensitive individuals.

Animal studies indicate that formaldehyde is a carcinogen. The American Conference of Governmental Industrial Hygienists (ACGIH) has identified formaldehyde as a "suspected human carcinogen" and sets a ceiling threshold limit value (TLV-C) of 0.3 ppm.

5.2.5.1 Checklist

• Records should be examined for evidence of recent renovation: painting, installation of plywood or particleboard, replacement of carpets, and installation of new furniture.
• Enquire about cleaning procedures.

5.2.5.2 Measurement Methods and Equipment

Monitors for formaldehyde include grab, continuous, and time-averaged samplers. Some equipment can provide direct readouts of formaldehyde in parts per million, whereas others require laboratory analysis of the samples.

a. Direct-reading tubes

This method employs detector tubes containing a substance that reacts with formaldehyde to produce a measurable colour change. Tubes are available that span several sensitivity ranges. Concentrations are read directly from the calibrated tube by the length of the stain. The tubes require a hand-operated or mechanical pump.

This method is only marginally sensitive at normal indoor air levels but may be useful for source identification and evaluation. Some samplers can measure in the range of 0.2-5 ppm.

b. Chemical analysis

In chemical analysis, formaldehyde is first collected in a sorption medium, then treated chemically and analysed to determine its concentration.

Passive samplers are small portable dosimeters that sample by diffusion onto a treated medium. The sample is analysed by the investigator or in a laboratory using the colorimetric or chromatographic method. Passive samplers are inexpensive, require little training to deploy, and involve little equipment. The sensitivity is good in the ppb, and an average formaldehyde level is determined for the measurement period, usually one day to one week.

The active sampling methods require a pump and bubbler. Some training is recommended, and solutions or solid sorbents must be prepared and processed in a laboratory.

c. Electrochemical detector

The electrochemical detector is a direct-reading active analyser. Formaldehyde is electrochemically reacted at the sensing electrode, generating a current in proportion to the concentration. A small internal air pump samples the air continuously. The minimum detectable level is in the 0.02-0.05 ppm range.

Advantages of the unit are portability, quickness of response, simplicity of operation, and continuous measurement capability. Disadvantages are the cost, the need for some training for calibration and maintenance, and the limited lifetime of the sensor.

5.2.5.3 Strategy for Remediation

Formaldehyde should be minimized in indoor air through both source and ventilation control methods.

Source control methods include:

• removing or reducing the source (selecting products with reduced emission levels, relocating contaminant-producing materials to a better-ventilated space)
• sealing the source with a barrier, such as polyurethane varnish
• off-gassing furnishings and building materials in storage prior to installation.

Ventilation control methods include:

• increasing the flow of outside air during the occupied and non-occupied hours
• controlling air pressure relationships (local exhausting, eliminating pollutant pathways)
• controlling source/distribution relationships (relocating occupants, avoiding recirculation of contaminated air).