What this is
What is a thermal stress assessment?
What is a thermal stress assessment?
It is a structured evaluation of heat or cold stress risk built from environmental readings, workload, and clothing, scored against ACGIH TLV and ISO 7243. It drives work-rest cycles, hydration or warm-drink provision, and acclimatisation planning rather than producing a one-off pass or fail.
When is a thermal stress assessment completed?
When a task, area, or worker population is new or has materially changed, and again on a seasonal cycle since ambient conditions shift. It is also triggered by a complaint, a permit requirement, a plant change, or after an incident.
Why does the template score environment and clothing separately from worker factors?
Because the same air temperature produces very different risk depending on work rate, insulation, and acclimatisation. Scoring them as separate blocks lets the assessor see which lever, engineering control, clothing, or rest cycle, actually moves the residual band.
Scope
When is a thermal stress assessment required?
This assessment covers heat or cold stress risk for a specific task, area, or population. It is not the place for a single incident's aftermath or for a role's general fitness requirements, which sit in other templates.
Use this template when
- A task, area, or worker population being assessed is new or has materially changed
- The seasonal cycle has come round, or ambient conditions have shifted enough to warrant a re-check
- A complaint, permit requirement, plant change, or incident has triggered the need for one
- Workers move repeatedly between hot and cold zones and the transition itself needs assessing, not just each zone alone
- A linked record needs this one to exist: links Site, Job, Worker
Do not use it for
- Fitness for Duty Assessment, which determines whether an individual worker can perform their role safely, not whether an environment is safe to work in.
- Impairment Concern Record, which documents a single observed concern about a worker, not an environmental hazard.
- Workload Review, which is the right template when fatigue from hours or pace is the concern rather than temperature.
- Health Screening Event Record, which covers periodic health checks rather than environmental risk assessment.
- Anything outside KnowHealth, which belongs in the workspace that owns that process.
Compliance mapping
Which ACGIH TLV requirements does this satisfy?
The basis here is guidance rather than a single binding regulation, so the mapping cites the provision at the level the source actually supports; local occupational exposure limits will typically incorporate these values by reference.
| Clause | Requirement | Where it lands |
|---|---|---|
| ACGIH TLV — heat stress and heat strain | Work rate, clothing insulation, and acclimatisation are assessed alongside environmental readings before a risk band is assigned | Work and clothing |
| ACGIH TLV — cold stress | Wind chill or an equivalent cold index is recorded, and clothing adequacy against heat loss is separately assessed | Environment |
| ISO 7243 — WBGT index for hot environments | A recognised index, WBGT or wind chill, is calculated rather than relying on air temperature alone | Environment |
| ACGIH TLV — acclimatisation | New starters and workers returning from leave are identified as higher risk and given an acclimatisation period | Individual factors |
| ACGIH TLV — work-rest regimen | Work-rest cycles are formally defined where the residual band indicates a need, not left informal | Controls |
| ACGIH TLV — hydration and self-pacing | Hydration is provided at the workplace, and a buddy system covers workers who cannot recognise their own symptoms | Controls |
| ISO 7243 — periodic review | A next review date is set and a risk assessment reference is linked wherever the residual band is not low | Outcome |
What it does not cover
- A residual band assigned without a work-rest cycle being defined, which leaves the control that actually manages the risk undecided.
- Transitions between extremes marked frequent with no distinct assessment of that transition, which treats a genuine stressor as if it were covered by assessing each zone alone.
- Acclimatisation period recorded as No for a new starter, which leaves the highest-risk population in the workforce unprotected in their first days.
- A WBGT or wind chill index left blank while the residual band is high or above, which means the band was estimated rather than calculated.
- Buddy system marked None in an extreme environment, which removes the only mechanism for catching a worker who cannot recognise their own symptoms.
Global
Thermal Stress Assessment requirements by country
Heat and cold stress sit mostly in general duty-of-care and occupational exposure frameworks rather than a single global statute, and how ACGIH and ISO values get enforced differs sharply by jurisdiction.
OSHA General Duty Clause, and state-level heat standards such as California and Washington
OSHA has no single federal heat standard and enforces heat risk through the General Duty Clause, while several states have adopted specific mandatory heat illness prevention rules with defined water, rest, and shade triggers.
Whether Work Rest Cycles Defined needs to match a specific regulatory trigger depends entirely on which state the site sits in.
Workplace (Health, Safety and Welfare) Regulations and equivalent EU framework directives
Regulation sets a duty to provide a reasonable working temperature and manage extremes as a hazard under general risk assessment duties, rather than prescribing ACGIH-style numeric limits directly.
ACGIH TLVs function as the technical benchmark an assessor points to, not as the legal instrument itself.
Model Work Health and Safety Regulations and Safe Work Australia thermal comfort guidance
The primary duty holder must manage risks to health and safety so far as reasonably practicable, with thermal comfort guidance referencing WBGT-style indices consistent with ISO 7243.
The Environment section's index calculation is what converts a general duty into a defensible, evidenced decision.
How to complete it
How to complete a thermal stress assessment, step by step
Correctly filled fields still leave four judgement calls that decide whether the assessment holds up when conditions push toward the extreme end of the band.
Where Transitions Between Extremes is Frequent, check whether Transitions Per Shift and the associated controls reflect that reality, or whether the assessor simply scored the freezer and the cook room as two unrelated environments.
Engineering Controls Applied and Work Rest Cycles Defined being marked Yes should mean they operate on the shift being assessed, not that a policy exists somewhere. The judgement call is whether the assessor observed the control in use.
A role can have an acclimatisation policy while a specific new starter on the assessed shift has not completed it. The field needs to reflect the people present, not the general policy.
Health Surveillance Indicated should track the residual band and the population's vulnerability, not default to No because surveillance is administratively inconvenient to arrange.
What auditors find
Most common thermal stress assessment findings
Recurring gaps in how this assessment gets completed, and the fix each one implies.
| Finding | Clause | What fixes it |
|---|---|---|
| WBGT or wind chill index left blank while air temperature alone drives the band | ISO 7243 — WBGT index for hot environments | Require the index field whenever Stress Type is Heat or Both |
| Transitions Between Extremes marked Frequent with Transitions Per Shift left blank | ACGIH TLV — heat and cold stress, combined exposure | Make Transitions Per Shift required whenever transitions are Occasional or Frequent |
| Acclimatisation Period Provided marked Yes as a blanket answer for the whole crew assessed | ACGIH TLV — acclimatisation | Prompt the assessor to confirm new starters specifically, not the crew as a whole |
| Work Rest Cycles Defined marked Informal for a residual band of High or above | ACGIH TLV — work-rest regimen | Flag any High-or-above band paired with an Informal or No control field for review before closure |
| Risk Assessment reference left blank despite Action Required being Yes | ISO 7243 — periodic review | Block closure until a linked risk assessment or CAPA reference is entered |
| Next Review Due left as a distant default date regardless of the residual band assigned | ISO 7243 — periodic review | Shorten the default review interval automatically for High, Very high, and Extreme bands |
Case in point
Case in point: the assessment that scored two rooms and missed the corridor
A dairy processor assessed its chill store separately from its pasteurising area, both came back Low or Medium, and closed the assessment. Workers moved between the two roughly fifteen times a shift carrying product, a route the assessment never scored because neither room, taken alone, looked like a problem.
After a worker collapsed on the connecting walkway, a reassessment found the transition itself, repeated shifts from minus two to over thirty degrees with no acclimatisation period for a recent starter, produced a Very High residual band once treated as its own stressor. The template's Transitions Between Extremes and Transitions Per Shift fields exist specifically to catch what two isolated room scores cannot.
The template
The template, field by field
The form exactly as it installs. Every field, option, score and conditional rule is editable, and the links to other templates come with it.
6 sections
- Reference
- HLT-040
- Archetype
- Assessment
- Record ID
- THS-2026-000
- Scoring
- Risk band
- Direction
- High is bad
- Singleton
- No
- Basis
- ACGIH TLV, ISO 7243
- Links
- Links Site, Job, Worker
- Tags
- Health, Thermal
- Sections
- 6
- Fields
- 52
- Follow up fields
- 3
- Repeating sections
- 0
- Links out
- 3
Header
12 fieldsAssessment ID*
Auto sequence. Format TSA-2026-000.
The record's own ID. Other templates point at this value.
Status*
Drives who this goes to next.
- Planned2 pts
- In progress2 pts
- Complete3 pts
- Deferred0 pts
- Open0 pts
- Closed3 pts
- Overdue0 pts
Date and Time*
Completed By*
Site*
Site ID*
Format SITE-000.
Links to FDN-001 Site ID
Area*
The area within the site.
Exact Location
Drop a pin for anything hard to find.
Both Directions Matter Here
A meat plant has cold stores at minus twenty and cook rooms above thirty, sometimes twenty metres apart. People move between them repeatedly through a shift.
Stress Type*
Assessment Trigger*
Workers Covered*
Environment
8 fieldsAir Temperature*
Humidity Percent
Air Movement*
- Good3 pts
- Some2 pts
- Still0 pts
Radiant Heat Source
- None3 pts
- Some1 pt
- Significant0 pts
WBGT Or Wind Chill Index
Exposure Duration Per Occasion*
- Yes3 pts
- Partly1 pt
- No0 pts
Transitions Between Extremes*
Repeated movement between freezer and cook room is a distinct stressor beyond either alone.
- None3 pts
- Occasional1 pt
- Frequent0 pts
Transitions Per Shift
Work and clothing
6 fieldsWork Rate*
- Light3 pts
- Moderate2 pts
- Heavy0 pts
Clothing Insulation*
- Appropriate3 pts
- Marginal1 pt
- Inadequate0 pts
Clothing Restricts Heat Loss
Waterproof and chain mail layers trap heat in warm areas.
- No3 pts
- Some1 pt
- Significantly0 pts
PPE Adds Thermal Load*
- No3 pts
- Some1 pt
- Significantly0 pts
Cold Weather Gear Provided
- Yes, full3 pts
- Partial1 pt
- No0 pts
Gloves Allow Dexterity
- Yes3 pts
- Marginal1 pt
- No0 pts
Individual factors
3 fieldsAcclimatisation Period Provided*
New starters and those returning from leave are at highest risk in the first days.
- Yes3 pts
- Partly1 pt
- No0 pts
Health Conditions Considered*
- Yes3 pts
- No0 pts
Medication Effects Considered
- Yes3 pts
- No0 pts
Controls
9 fieldsEngineering Controls Applied*
- Yes4 pts
- Partly2 pts
- None0 pts
Work Rest Cycles Defined*
- Yes3 pts
- Informal1 pt
- No0 pts
Rest Area At Neutral Temperature*
- Yes3 pts
- Marginal1 pt
- No0 pts
Hydration Provided*
- Yes, at the workplace3 pts
- Available elsewhere1 pt
- No0 pts
Warm Drinks Provided For Cold Work
- Yes3 pts
- No0 pts
Buddy System In Place*
Somebody suffering thermal stress often cannot recognise it in themselves.
- Yes3 pts
- Informal1 pt
- None0 pts
Symptom Awareness Training Given*
- Yes3 pts
- No0 pts
Emergency Response Defined*
- Yes3 pts
- No0 pts
Lone Working Prohibited In Extremes*
- Yes3 pts
- No0 pts
Outcome
14 fieldsResidual Band*
- Low, 1 to 45 pts
- Medium, 5 to 94 pts
- High, 10 to 142 pts
- Very high, 15 to 191 pt
- Extreme, 20 to 250 pts
Exposure Acceptable*
- Yes3 pts
- Marginal1 pt
- No0 pts
Health Surveillance Indicated*
- No3 pts
- Yes1 pt
Risk Assessment
Risk ID
Format RSK-2026-00000.
Links to FDN-012 Risk ID
Action Required*
Raise the action record, then enter its reference here.
- No2 pts
- Yes0 pts
Priority
- High0 pts
- Medium1 pt
- Low3 pts
CAPA ID
Format CAPA-2026-00000.
Links to FDN-014 CAPA ID
Action Owner
Next Review Due*
Occupational Hygienist*
Signature*
Safety Lead*
Second Signature*
HLT-040 · record IDs look like THS-2026-000 · Links Site, Job, Worker
Open in KnowellaRun it with agents
From a document you fill in to a programme that runs itself
The assessment scores a moment in time well. Catching seasonal drift, transition exposure, and stalled follow-up actions across every site is the harder, ongoing problem.
Holds every thermal stress assessment against site and worker history, flags overdue reviews, and tracks whether a promised risk assessment or CAPA reference actually gets entered.
Correlates seasonal and site environmental data with assessment triggers, so a re-check happens when conditions shift rather than only on a fixed calendar date.
Watches for High-or-above residual bands paired with informal or missing controls, and surfaces sites where work-rest cycles exist on paper but not on the floor.
Coordinates the crew across KnowHealth, KnowEnviro and KnowSafe, rolls exposure and completion into one view, and holds every write for your approval before it touches a record.
This template lives in KnowHealth — employee wellbeing. Exposure monitoring, health surveillance, case management and return to work.
Meet KnowHealth→Glossary
Thermal Stress Assessment definitions and key terms
- WBGT
- Wet Bulb Globe Temperature, a composite index of air temperature, humidity, radiant heat, and air movement used by ISO 7243 to estimate heat stress more accurately than air temperature alone.
- Acclimatisation
- The physiological adaptation to heat or cold that develops over days of repeated exposure; new starters and returning workers lack it and carry the highest risk in their first days.
- Residual band
- The risk classification, low through extreme, remaining after environment, work rate, clothing, and controls are all scored together, rather than the raw environmental reading alone.
- Work-rest cycle
- A defined pattern of work periods and recovery breaks calibrated to the residual risk band, intended to keep cumulative exposure within safe limits.
- Threshold limit value (TLV)
- An ACGIH-published exposure guideline, here for heat and cold stress, intended as a level below which nearly all workers can be repeatedly exposed without adverse effect.
FAQ
Frequently asked questions about thermal stress assessment
What is the thermal stress assessment template based on?+
ACGIH threshold limit values for heat and cold stress, and ISO 7243 for the WBGT index used to score hot environments. Both are widely adopted guidance rather than a single binding global statute.
What sections does the thermal stress assessment contain?+
Six sections: Header, Environment, Work and clothing, Individual factors, Controls, and Outcome. Together they hold 52 fields, 36 of them required.
How often is a thermal stress assessment raised?+
Seasonally as a matter of course, and whenever a task, area, or population is new or has materially changed. A complaint, permit requirement, plant change, new installation, or incident also triggers one.
Why does the template separately assess transitions between hot and cold areas?+
Because repeated movement between extremes, common in meat and dairy processing, is a distinct stressor beyond either environment scored alone, and controls calibrated to one zone can fail entirely on the transition.
How is a thermal stress assessment scored?+
It produces a residual risk band from Low to Extreme, where high is bad. The band, not any single reading, determines whether work-rest cycles, hydration provision, and health surveillance are required.
Can this template be changed?+
Yes. Every field, option, score, and conditional rule is editable, and the links to Site, Job, and Worker records carry over. Most teams install it as it is, run it for a cycle, then adjust.
Keep going
Related templates and programmes
Industries this is written for
Programmes this belongs to
Used together in Wellbeing and Mental Health
Wellbeing Survey
Asks workers about workload, support, stress and how they are coping
Psychosocial Risk Assessment
Assesses workplace factors that affect mental health, including demand, control, support and change
Workload Review
Reviews whether workload, hours and staffing are sustainable for a team
Wellbeing Program Plan
Sets out what wellbeing support is available and how people access it
Support Referral Record
Records that a worker was pointed towards support services, without recording why
Fitness for Duty Assessment
Assesses whether a worker is currently able to perform their role safely
Written and reviewed by
Siddarth Singh
Founder & Chief Executive Officer, Knowella
Certified Safety Professional and industrial and systems engineer with more than a decade inside food supply chain, freight and manufacturing operations. This page was written against the current text of the standards it cites, not against secondary summaries of them.
- Certified Safety Professional (CSP), Board of Certified Safety Professionals
- MBA, University of Chicago Booth School of Business
- MS and BS, The Ohio State University, Industrial and Systems Engineering
- Six Sigma Black Belt
Sources and last review. Reviewed 16 August 2026 against:
- ACGIH Threshold Limit Values — Heat Stress and Strain
- ACGIH Threshold Limit Values — Cold Stress
- ISO 7243:2017 — Ergonomics of the thermal environment, WBGT index
- Safe Work Australia — Managing the risks of working in heat
This page is general guidance, not legal advice. Confirm requirements with your jurisdiction’s regulator.