Thermal Work Limit Chart
Thermal Work Limit (TWL)
|
Working zones |
Interventions |
Rehydration Schedule |
Work-Rest Schedule(minutes) |
|
Low Risk TWL: 140 – 200 |
No limits
on self-paced work for educated hydrated workers |
Light Work
0.6 – 1 Litres/Hour |
Safe for all continuous self-paced work |
|
Medium Risk TWL: 115 – 140 |
Additional precautions required Â
|
Light Work
1-1.2 Litres/Hour |
Safe for all continuous self-paced work |
| Heavy Work
>1.2 Litres/Hour |
Continuous paced work
45 Work – 15 Rest |
||
|
High Risk TWL: < 115 |
Strict Work – Rest Cycling required
|
All Work
>1.2. Litres/Hour |
Light Work
45 Work – 15 Rest |
| Heavy Work
20 Work – 40 Rest |
TWL LEGEND
- Self-paced work – Workers must be allowed to adjust their work rate according to environmental conditions. Paced work is when the work rate is not under the worker’s controls
- Unacclimatized workers are defined as new workers ot those who have been of work for more than 14 days due to illness or on vacation leave (in a cool climate area)
- Light work – sitting or standing, light arm work
- Heavy Work – carrying, climbing, lifting, pushing, whole body work
Note: At high workloads and or thermal stress, sweat rate exceed 1.2 Litres/Hour. Increasing fluid intake much above this level is not practical due to gastric discomfort as the upper limit for gastric absorption is ~ 1.5 Litres/Hour so control solutions to improve thermal conditions should be implemented in addition to providing adequate hydration to replace sweat lost.
Additional factors contributing to heat illness
- Wearing of additional PPE e.g. chemical suit; RPE
- Heavy or forced paced workload
- High level of task complexity e.g. precision operation
- High level of environmental noise or vibration
- Body Mass Index (BMI) greater than 30
- Aging worker / Unfit worker
- Medical condition or medications taken.
Asalamualikum,
The above thermal chart index details from which standatd uk/Usa/oman?
Wa aleykum Salam
Dear Shabeer,
This is the chart used by the Industrial Hygienists in PDO, at least it was back in 2019.
Hope this helps,
EntirelySafe.com team