S-2.1, r. 13 - Regulation respecting occupational health and safety

Schedule Disposition versions

2020-09-17

SCHEDULE V

(ss. 121, 122, 123 and 124)

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.

Exposure to temperatures in excess of those in Table 1 is permitted under the following conditions: the worker must be under medical supervision and it must be proven that his tolerance for working in heat is greater than that of the average worker.

Table 1

PERMISSIBLE HEAT EXPOSURE LIMIT VALUES, IN °C (WBGT °C (WBGT)

          Alternate Regimen                              Work load
               work/rest
                                        ___________________________________________

                                                 light      moderate      heavy   
                                                 work         work        work   

Continuous work                                   30.0        26.7        25.0

Work 75%, rest 25% (every hour)                   30.6        28.0        25.9

Work 50%, rest 50% (every hour)                   31.4        29.4        27.9

Work 25%, rest 75% (every hour)                   32.2        31.1        30.0
               

Chart

PERMISSIBLE HEAT EXPOSURE VALUES

        ____________________ continuous work
        - - - - - - - - - - - - - - - - -  75% work —  25% rest
        __________• _________ 50% work — 50% rest         every hour
        __________• • ________ 25% work — 75% rest

Method of measurement

WBGT values are measured as follows:

(1) The range of the dry and the natural wet bulb thermometer must be between -5 °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-centimetre 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: accuracy: ± 0.5 °C) must be set at 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.

The WBGT values may also be measured using a direct-reading measuring instrument.

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 classified 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: from 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 assigned to a particular category by measuring the metabolism of the man at work, namely by estimating his metabolism using the following Table 2:

Table 2

ASSESSMENT OF WORK LOAD AND 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 of 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 both arms...................  filing metal, planning wood,
                                               raking a garden
Moderate work using both arms................  cleaning a floor, beating a carpet
Heavy work using the body ...................  railroad track laying, digging,
                                               barking trees 

C. Basal metabolism: kcal/h

Basal metabolism: minimum quantity of calorific energy used when the body is at
complete rest.

Sample calculation: use of 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 used:

(a) Astrand P.O., Rodahl K., Textbook of Work Physiology, New York, San Francisco, McGraw Hill Book Company, 1979;

(b) Ergonomics Guide to Assessment of Metabolic and Cardiac Cost of Physical Work, Amer, Id. Hyg. Assoc. J., 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., Passmore R., Energy, Work and Leisure, London, Heinemenn Educational Books, 1967.

Alternate work/rest regimen

The permissible exposure limit values specified in Table I 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. Limits applicable to continuous work correspond to the following conditions: a 5-day week, an 8-hour working day with a short pause (about a half-hour) for a meal. 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 when the worker’s average metabolic rate will be higher.

When 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 the 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:

(M1) × (t1) + (M2) × (t2) + ... (Mn) × (tn)

M moyen = _____________________________________

(t1) + (t2) + ... (tn)

where M1, M2 and Mn are estimated metabolic rates for each of the worker’s work locations for the entire 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:

(WBGT1) × (t1) + (WBGT2) × (t2) + ... (WBGTn) × (tn)

WBGT moyen = ___________________________________________

(t1) + (t2) + ... (tn)

where WBGT1, WBGT2, WBGTn represent values calculated in WBGT for various tasks at rest and work stations occupied during all time periods and t1, t2, tnconstitute the time in minutes spent at each rest and work station.

When exposure to hot environmental conditions is continuous for several hours or the entire work day, the time-weighted average value must be computed as an hourly time-weighted average, i.e. t1 + t2 + ,,, tn = 60 minutes. Where exposure is intermittent, the time-weighted average values must be computed as two-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

O.C. 885-2001, Sch. V; O.C. 889-2020, s. 7.

2012-09-01

SCHEDULE V

(s. 121, 122, 123 and 124)

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.

Exposure to temperatures in excess of those in Table 1 is permitted under the following conditions: the worker must be under medical supervision and it must be proven that his tolerance for working in heat is greater than that of the average worker.

Table 1

PERMISSIBLE HEAT EXPOSURE LIMIT VALUES, IN °C (WBGT °C (WBGT)

          Alternate Regimen                              Work load
               work/rest
                                        ___________________________________________

                                                 light      moderate      heavy   
                                                 work         work        work   

Continuous work                                   30.0        26.7        25.0

Work 75%, rest 25% (every hour)                   30.6        28.0        25.9

Work 50%, rest 50% (every hour)                   31.4        29.4        27.9

Work 25%, rest 75% (every hour)                   32.2        31.1        30.0
               

Chart

PERMISSIBLE HEAT EXPOSURE VALUES

	____________________ continuous work
	- - - - - - - - - - - - - - - - -  75 % work —  25 % rest
	__________• _________ 50 % work — 50 % rest	 every hour
	__________• • ________ 25 % work — 75 % rest

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-centimetre 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: accuracy: ± 0.5 °C) must be set at 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 classified 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: from 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 assigned to a particular category by measuring the metabolism of the man at work, namely by estimating his metabolism using the following Table 2:

Table 2

ASSESSMENT OF WORK LOAD AND 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 of 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 both arms...................  filing metal, planning wood,
                                               raking a garden
Moderate work using both arms................  cleaning a floor, beating a carpet
Heavy work using the body ...................  railroad track laying, digging,
                                               barking trees 

C. Basal metabolism: kcal/h

Basal metabolism: minimum quantity of calorific energy used when the body is at
complete rest.

Sample calculation: use of 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 used:

(a) Astrand P.O., Rodahl K., Textbook of Work Physiology, New York, San Francisco, McGraw Hill Book Company, 1979;

(b) Ergonomics Guide to Assessment of Metabolic and Cardiac Cost of Physical Work, Amer, Id. Hyg. Assoc. J., 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., Passmore R., Energy, Work and Leisure, London, Heinemenn Educational Books, 1967.

Alternate work/rest regimen

The permissible exposure limit values specified in Table I 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. Limits applicable to continuous work correspond to the following conditions: a 5-day week, an 8-hour working day with a short pause (about a half-hour) for a meal. 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 when the worker’s average metabolic rate will be higher.

When 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 the 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:

(M1) × (t1) + (M2) × (t2) + ... (Mn) × (tn)

M moyen = _____________________________________

(t1) + (t2) + ... (tn)

where M1, M2 and Mn are estimated metabolic rates for each of the worker’s work locations for the entire 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:

(WBGT1) × (t1) + (WBGT2) × (t2) + ... (WBGTn) × (tn)

WBGT moyen = ___________________________________________

(t1) + (t2) + ... (tn)

where WBGT1, WBGT2, WBGTn represent values calculated in WBGT for various tasks at rest and work stations occupied during all time periods and t1, t2, tn constitute the time in minutes spent at each rest and work station.

When exposure to hot environmental conditions is continuous for several hours or the entire work day, the time-weighted average value must be computed as an hourly time-weighted average, i.e. t1 + t2 + ,,, tn = 60 minutes. Where exposure is intermittent, the time-weighted average values must be computed as two-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

O.C. 885-2001, Sch. V.