Heat generated by activity

The body’s activity produces energy and influences thermal balance with the environment. Metabolic rate represents this contribution in assessment models. It does not describe external temperature alone and is not equivalent to heart rate. Estimating it helps interpret occupational heat stress or cold exposure.

Units must not be mixed

It may be expressed in watts or relative to body surface area in watts per square metre. Enter data in the units required by the method. Copying a number from a table without identifying its unit or definition can substantially alter the result, even when the software accepts it without an error.

Assess the task, not only the job title

One job may alternate walking, carrying, handling and waiting. Assessment must describe these phases, their durations and intensities. Labels such as light or heavy work require a shared technical criterion. Observer impressions may be insufficient where there are brief exertions, repetitive movements or conditions making normal task execution more difficult.

Methods and representativeness

Table-based estimates or more precise methods can be used where the objective requires them. Choice depends on acceptable uncertainty and the situation. Physiological measurements require professional interpretation: other factors may modify the observed response. The report must state the procedure and explain which activities it covers and which it excludes.

An operational-change example

In a hypothetical situation, a conveyor replaces manual box carrying. Room temperature remains unchanged, but activity and therefore heat production change. The previous thermal assessment may no longer represent the work. In a cold area, reduced activity may also increase the need for protection against heat loss.

Using the result

Interpret metabolic rate alongside clothing, air, radiation and the method’s other variables. It is not an individual performance indicator or a basis for demanding faster work. It supports adjustments to work organisation, breaks and technical measures. Decisions must account for variation across the shift and the needs of particularly vulnerable people.