What HAL means
Hand Activity Level estimates manual activity by considering repetition and continuity of work. In ACGIH’s methodology it is combined with normalised peak force to assess exposure. An isolated HAL score is therefore not a complete result: two operations with a similar pace may require very different forces.
Where it is useful
It can help study hand-intensive operations such as certain assembly, food preparation or component finishing tasks. Observation should represent usual cycles and their variations. Hands should be analysed separately where their functions differ: holding an item and making cuts, for example, do not necessarily create the same demand.
Choosing the instrument is part of selecting the ergonomic assessment methods available for each exposure.
What information to collect
Activity, force used, recovery periods, tools and task duration are documented. Force estimation requires the relevant procedure, through observation or measurement and worker participation as specified by the method. Video can help reviewers compare assessments, but does not by itself reveal grip force.
What its reference values mean
The methodology includes action and exposure references. NIOSH notes that the 2018 revision substantially changed application of the criterion compared with 2001. A report should identify the edition used and avoid combining graphs, formulas or interpretations from different versions. ACGIH’s technical values do not automatically become legal limits in every country.
Prevention example
In a hypothetical manual cutting example, pace changes little after a tool is renewed, but the required force falls. Assessing movement count alone would miss that improvement. The study reassesses both components and checks sharpness maintenance, handle design and recovery. The intervention must be sustained under real production conditions, not only during the trial.
What it does not replace
HAL does not diagnose carpal tunnel syndrome or cover all upper-limb ergonomics. Postures, contact with edges, vibration and other demands require specific attention. Assessment should lead to changes in tools, process and organisation, with exposure and discomfort monitored. It is not used to select workers able to tolerate a poorly designed job.
