Estimating metabolic rate

Metabolic rate can be estimated using either tabulated values as given here, or alternatively by referring to British Standard BS 8966

Level	Method	Accuracy	Inspection of the workplace
I	A – Classification according to kind of activity	Rough information where the risk of error is very great	Not necessary
	B – Classification according to occupation		Information on technical equipment, work
II	A – Use of tables of group assessment	High error risk; accuracy ± 15%	Time study necessary
	B – Use of estimation tables for specific activities
	C – Use of heart rate user defined conditions		Not necessary
III	Measurement	Risk of errors within the limits of the accuracy of the measurement and of the time study; accuracy ±5%	Time study necessary

Classification of metabolic rates by activity.  (ISO 8996)

Class	Mean metabolic rate  (Wm-2)	Example
Resting	65	Resting
Low	100	Sitting at ease/standing
Moderate	165	Sustained hand/arm work
High	230	Intense work
Very high	290	Very intense to maximum activity

Classification by occupation.  (Examples from ISO 8996)

	Occupation	Metabolic rate (Wm-2)
Craftsmen:
	Bricklayer	110  to  160
	Carpenter	110  to  175
	Glazier	90    to  125
	Painter	100  to  130
Agriculture:
	Gardener	115  to  190
	Tractor driver	85    to  110
	etc.

Calculation of average metabolic rate over a period where a number of tasks and activities are carried out.  (BS EN 8996).

	Duration (s)	Metabolic rate (Wm-2)
Walk in factory 4 km h-1	35	165
Carry sack of 30 kg	50	250
Standing	25	70
Time weighted average  =  200 Wm-2

Estimated Increases in Metabolic rate due to wearing PPE

Increase in metabolic rate due to wearing RPE (W.m-2)

PPE		Resting	Low metabolic rate	Moderate metabolic rate	High Metabolic rate	Very high metabolic rate
Safety shoes/short boots		0	5	10	15	20
Safety boots (long)		0	10	20	30	40
Respirator (low/moderate performance e.g. P1, P2)		5	10	20	30	40
Respirator (high performance e.g. P3)		5	20	40	60	80
Self contained breathing apparatus		10	30	60	95	125
Light, water vapour permeable chemical coverall (e.g. Disposable)		5	10	20	30	40
Chemical protective water vapour impermeable PPE e.g. polyvinyl chloride (PVC) with hood, gloves and boots		10	25	50	80	100
Highly insulating, water vapour semi-permeable clothing e.g. firefighter’s helmet, tunic, over trousers, gloves and boots		15	36	75	115	155

According to BS 7963, the following needs to be considered:

• Metabolic rate values have been rounded off to the nearest 5 W.m^-2.
• Respirator classification defined in BS EN 143 (1991).
• As can be seen from the estimated increases in metabolic rate, very high metabolic rate cannot be maintained when wearing some forms of PPE.  Here job redesign would be necessary if engineering controls were not possible.
• Do not add footwear induced increase in metabolic rate for sedentary tasks.
• If more accurate methods of obtaining metabolic rate values are required, refer to BS EN 8996.
• If metabolic rate is measured instead of estimated, corrections for the increased metabolic rate are not necessary.

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