* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * INFORMATION ALERT * * * * Produced by: Saskatchewan Human Resources, * * Labour and Employment * * Provided by: Canadian Centre for Occupational Health and Safety * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * INDOOR AIR QUALITY ... MEASURING FRESH AIR SUPPLY RATES The carbon dioxide exhaled by the occupants of a space will accumulate during the workday. In a space which ahs been occupied during the day, the carbon dioxide concentration can be used to measure the fresh air supply rate. The relationship is indicated in the table of the information sheet, 'Indoor Air Quality ... Fresh Air Supply'. A direct reading carbon dioxide instrument may be used to measure concentrations. Such an instrument will accurately measure carbon dioxide levels provided that frequent calibration with gases of known carbon dioxide concentration is performed. If only a limited number of spaces are of concern the use of direct reading colourimetric tubes may be more apporpriate. Technically trained personnel are not required to use these tubes. The carbon dioxide concentration can usually be estimated to within 100 ppm with colorimetric tubes. Colourimetric tubes are glass tubes filled with chemically treated granules which change colour in the presence of carbon dioxide. A hand held pump is used to draw air through the tube. A numerical scale is printed on the side of the tube. The granules inside the tube will change colour (stain). The length of stain can be matched to the scale on the tube. Most safety equipment suppliers will market a brand of colourimetric tube and pump. Carbon dioxide tubes which will indicate levels in the range from 300 parts per million (ppm) to 2000 ppm or higher are required for this type of testing. These are typically the lowest range of carbon dioxide tubes available. When measuring carbon dioxide levels by any method, avoid breathing in the direction of the probe or tube. Exhaled breath contains approximately 50,000 ppm of carbon dioxide. If using one of the tube systems it is often best to lay the pump down after drawing air through the tube and momentarily leaving the area to avoid inadvertent contamination by your own breath. Testing is normally performed in the mid to late afternoon to allow occupant generated carbon dioxide to accumulate. Occupied areas where fresh air is not being adequately supplied will exhibit elevated carbon dioxide levels (over 1000 ppm and/or significantly higher than other areas). Poor air exhange/inadequate air supply may be due to blocked supply air diffusers, an unblanced system, an improperly set fresh-air inlet damper or other ventialtion system deficiency. Unless the cause is obvious (such as materials piled on top of a supply grill), the services of an experienced ventilation professional will be necessary. In an area where partial dividers are used to provide privacy and separation, tests are best performed at heights below the top of the dividers (preferably at the typical head height of an occupant). It is not unusual for fresh air supplied to this type of office layout to pass above the tops of dividers without reaching the worker's location. If carbon dioxide testing indicates that this may be occuring the simplest, usually effective, solution is to raise each divider 10 centimetres above the floor. This usually allows supplied air access down into the partitioned space. * * * * * * * * * * * * * * * * * * * * * * * *