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S-2.1, r. 11 - Regulation respecting the quality of the work environment

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SCHEDULE D
(ss. 37, 38, 39 and 40)
EVALUATION OF HEAT STRESS
Wet Bulb-Globe Temperature Index (WBGT) is computed by using the following equations:
(a) outdoors with solar load:
WBGT = 0.7 WB + 0.2 GT + 0.1 DB
(b) indoors or outdoors with no solar load:
WBGT = 0.7 WB + 0.3 GT
where: WB = natural wet-bulb temperature
DB = dry-bulb temperature
GT = globe thermometer temperature
To determine WBGT, the instruments required are a black globe thermometer, a natural (static) wet-bulb thermometer and a dry-bulb thermometer.
Heat exposures higher than those shown in Table I are permissible on the following conditions: the worker must be under medical supervision and it must be proven that his tolerance for working in heat is greater that that of the average worker.
Table I
PERMISSIBLE HEAT EXPOSURE LIMIT VALUES, IN °C (WBGT)
_________________________________________________________________________________
| | |
| | Work load |
| Alternate work/rest |___________________________________|
| regimen | | | |
| | light | moderate | heavy |
| | work | work | work |
|_____________________________________________|___________|___________|___________|
| | | | |
| Continuous work | 30.0 | 26.7 | 25.0 |
|_____________________________________________|___________|___________|___________|
| | | | |
| Work 75%, rest 25% (each hour) | 30.6 | 28.0 | 25.9 |
|_____________________________________________|___________|___________|___________|
| | | | |
| Work 50%, rest 50% (each hour) | 31.4 | 29.4 | 27.9 |
|_____________________________________________|___________|___________|___________|
| | | | |
| Work 25%, rest 75% (each hour) | 32.2 | 31.1 | 30.0 |
|_____________________________________________|___________|___________|___________|
Graph
PERMISSIBLE HEAT EXPOSURE LIMIT VALUES
Method of measurement
WBGT values are measured as follows:
(1) The range of the dry and the natural wet bulb thermometer must be between -50 °C and + 50 °C, with an accuracy of ± 0.5 °C. The dry bulb thermometer must be shielded from the sun and other radiant surfaces without restricting the airflow around the bulb. The wick of the natural wet bulb thermometer must be kept wet with distilled water for at least 30 minutes before the temperature reading is made. It is not enough to immerse an end of the wick into a reservoir of distilled water and wait until the wick becomes wet by capillarity; the wick must be wetted by direct application of water from a syringe one-half hour before each reading. The wick must extend over the bulb of the thermometer, covering the stem about one additional bulb length. The wick should always be clean and new wicks should be washed before being used.
(2) A globe thermometer, consisting of a 15-cm diameter hollow copper sphere painted on the outside with a matte black finish or equivalent, must be used. The bulb or sensor of the thermometer (range: -5 °C to + 100 °C with an accuracy of ± 0,5 °C) must be fixed in the centre of the sphere. The globe thermometer must be exposed at least 25 minutes before it is read.
(3) A stand must be used to suspend the 3 thermometers so that they do not restrict free air flow around the bulbs, and so that there is no obstacle between the heat sources and the wet bulb globe thermometer.
(4) Any other type of temperature sensor may be used that gives a reading identical to that of a mercury thermometer under the same conditions.
(5) The thermometers must be placed so that the readings are representative of the conditions in which the men work or rest, respectively.
Work load
The total heat load is the sum of the heat produced by the body and the environmental heat. Therefore, if the work is performed under hot environmental conditions, the workload category of each job must be established and the permissible heat exposure limit value pertinent to the work load evaluated against the applicable standard in order to protect the worker from exposure beyond the permissible limit.
The jobs performed by a worker must be classed in the following categories:
(a) light work: up to 200 kcal/h (sitting or standing to control machines, performing light hand or arm work, etc.);
(b) moderate work: from 200 to 350 kcal/h (walking about with moderate lifting and pushing, etc.);
(c) heavy work: form 350 to 500 kcal/h (pick and shovel work, etc.).
Table I thus gives the permissible heat exposure limit value for the specified work load.
An activity may be classed in a particular category by measuring the metabolism of the man at work or by estimating his metabolism using the following Table II:
Table II
ASSESSMENT OF WORK LOAD AVERAGE VALUES OF METABOLIC RATE DURING DIFFERENT ACTIVITIES
_________________________________________________________________________________
| | |
| A. Body position and movement | kcal/h |
|________________________________________________|________________________________|
| | |
| Sitting....................................... | 18 |
| | |
| Standing...................................... | 36 |
| | |
| Walking....................................... | 120-180 |
| | |
| Walking uphill................................ | Add 48 per metre rise |
|________________________________________________|________________________________|

_________________________________________________________________________________
| | | |
| | | |
| B. Type of work | average | Range |
| | (kcal/h)| (kcal/h) |
|______________________________________|_________|________________________________|
| | | |
| Handwork............................ |.........| 12-72 |
| light............................. | 24 | |
| heavy............................. | 54 | |
| | | |
| Work using one arm.................. |.........| 42-150 |
| light............................. | 60 | |
| heavy............................. | 108 | |
| | | |
| Work using both arms................ |.........| 60-210 |
| light............................ | 90 | |
| heavy............................ | 150 | |
| | | |
| Work using body..................... |.........| 150-900 |
| light............................ | 210 | |
| moderate......................... | 300 | |
| heavy............................ | 420 | |
| very heavy....................... | 540 | |
|______________________________________|_________|________________________________|
| | |
| Light handwork................................ |writing, knitting |
| Heavy handwork................................ |typing |
| Heavy work using one arm...................... |hammering in nails |
| |(shoemaker, upholsterer) |
| Light work using 2 arms....................... |filing metal, planning wood, |
| |raking a garden |
| Moderate work using 2 arms.................... |cleaning a floor, beating a |
| Heavy work using the body..................... |carpet railroad track laying, |
| |digging, barking trees |
|________________________________________________|________________________________|

_________________________________________________________________________________
| |
|C. Basal metabolism: 60 kcal/hre |
| |
| Basal metabolism: minimum quantity of calorific energy used when |
| the body is at complete rest |
|_________________________________________________________________________________|

_________________________________________________________________________________
| |
| Sample calculation: using a heavy hand tool on an assembly line | | |
|_________________________________________________________________________________|
| | |
| A. Walking along.............................. | 120 kcal/h |
| | |
| B. Intermediate value between heavy work | |
| using 2 arms and light work using | |
| the body................................... | 180 kcal/h |
| |________________________________|
| | |
| | 300 kcal/h |
| | |
| C. Basal metabolism........................... | 60 kcal/h |
| |________________________________|
| | |
| Total........................... | 360 kcal/h |
|________________________________________________|________________________________|
The tables in the following publications may also be utilized:
(a) Astrand P.O., and Rodahl K., Textbook of Work Physiology, New York, San Francisco, McGraw-Hill Book Company, 1979;
(b) Amer. Id. Hyg. Assoc. J., Ergonomics Guide to Assessment of Metabolic and Cardiac Cost of Physical Work, No. 32;
(c) Energy Requirements for Physical Work, Research Progress Report No. 30, Purdue Farm Cardiac Project, Agricultural Experiment Station, 1961;
(d) Durnin, J.V.G.A., and Passmore, R., Energy, Work and Leisure, London, Heinemann Educational Books, 1967.
Alternate work/rest regimen
The permissible exposure limit values specified in Table 1 and the Graph are based on the assumption that the WBGT value of the resting place is the same or very close to that of the work location. The permissible exposure limit values for continuous work are applicable where there is 5-day work week and an 8-hour work day with a short break (approximately half an hour) for meals. Higher exposure limits are permitted if additional rest periods are allowed. All breaks, including pauses and administrative or operational waiting periods during work may be counted as rest time when additional rest periods must be given because of high environmental temperatures.
A worker whose job is self-paced will spontaneously limit his hourly work load to 30-35% of his maximum physical performance capacity, either by setting an appropriate work speed or by interspersing unscheduled breaks. Thus the daily average of the worker’s metabolic rate seldom exceeds 330 kcal/h. However, within an 8-hour work shift, there may be periods where the worker’s average metabolic rate will be higher.
Where the WBGT index of the work location is different from that of the rest area, a time-weighted average value should be used for both environmental heat and metabolic rate. When time-weighted average values are used, the curve to be referred to in the above graph is the solid line.
The time-rated average metabolic rate is determined by the following equation:
Maverage =(M1) × (t1) + (M2) × (t2) + ... (Mn) × tn)
_______________________________
(t1) + (t2) + ... (tn)
where M1, M2 and Mn are estimated metabolic rates for each of the worker’s work locations for the whole work period, and t1, t2 and tn are the time in minutes spent at each corresponding metabolic rate.
Similarly, the time-weighted average WBGT is determined by the equation:
WBGT average =
(WBGT1) × (t1) + (WBGT2) × (t2 + ... (WBGT) × (tn)
______________________________________________
(t1) + (t2 + ... (tn)
where WBGT1, WBGT2 and WBGTn are calculated values of WBGT for various jobs performed at rest areas and work locations occupied during total time periods, and t1, t2, tn are the times in minutes spent in the work locations and in each rest area.
Where exposure to hot environmental conditions is continuous for several hours or the entire work day, the time-weighted average must be computed as an hourly time-weighted average, i.e. t1 + t2 + tn + = 60 minutes. Where exposure is intermittent, the time-weighted averages must be computed as 2-hour time-weighted averages, i.e. t1 + t2 + tn = 120 minutes.
Scope of method
The WBGT method does not apply to unacclimatized workers who are physically incapable of performing a specific job or to workers who wear clothing especially adapted to certain dangerous tasks as protection against the heat.
R.R.Q., 1981, c. S-2.1, r. 15, Sch. D.
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