12. > 43 Tissue damage - Death
40 - 43 Failure of sweating mechanism
38 - 40 Limit set by WHO for avoidance of physiological strain
36.4 - 37.6 Normal core temperature
34 - 36.4 Shivering, decreased efficiency, confusion
30 - 34 Drowsiness, irregular heart rate, cramp
26 - 30 Loss of consciousness, severe impairment of respiratory and
cardiac functions
< 26 Death
61. WBGT Reference Values from ISO 7243
Metabolic
Rate Class
Metabolic
Rate W/m2
Reference Value of WBGT (C)
Acclimatised Non-acclimatised
0 <65 33 32
1 65 - 130 30 29
2 130 - 200 28 28
3 200 - 260 no air movement 25
with air movement 26
no air movement 22
with air movement 23
4 >260 no air movement 23
with air movement 25
no air movement 18
with air movement 20
62. ACGIH TLVs – Action Limit
Allocation of
work in work
cycle
Workload
Light Moderate Heavy V ery
heavy
75% to 100% 28.0 25.0 - -
50% to 75% 28.5 26.0 24.0 -
25% to 50% 29.5 27.0 25.5 24.5
0 to 25% 30.0 29.0 28.0 27.0
63. ACGIH TLVs
Allocation of
work in work
cycle
Workload
Light Moderate Heavy V ery
heavy
75% to 100% 31.0 28.0 - -
50% to 75% 31.0 29.0 27.5 -
25% to 50% 32.0 30.0 29.0 28.0
0 to 25% 32.5 31.5 30.5 30.0
64. TLV Clothing Corrections
ClothingType WBGT Correction
Work clothes (long sleeve and pants) 0
Cloth (woven material) coveralls o
Double layer woven clothing 3
SMS polypropylene coveralls 0.5
Polyolefin overalls 1
Limited use capour-barrier overalls 11
65. ISO Standards
7243 Estimation of heat stress usingWBGT
7730 Evaluation of moderate thermal
environments using PMV and PPD
7933 Analytical determination of heat stress
using the Predicted Heat Strain Index
7726 Instruments and methods
8996 Physiological methods
66. Predicted Heat Strain Index
Complex!
Based on heat balance equation
Solve using computer program
69. Predicted Heat Strain Index
Gives maximum allowable exposure
times based on
o Heat storage
o Water loss
70. Outdated heat stress indices
Effective temperature (ET)
Corrected effective temperature (CET)
Predicted four hour sweat rate (P4SR)
The heat stress index (HSI)
Index of thermal stress (ITS)
74. Assess Risk
using screening methods
WBGT Index
ISO 7243 or ACGIH TLVs
Expert analysis
PHS Index - ISO 7933
Expert analysis
Physiological measures
– ISO 9886
ISO 27726
Specification of equipment used
to measure thermal environment
ISO 28996
Estimation or measurement of
Metabolic rate
Identify Hazards
Identify Controls
A Structured Approach to Heat Stress Risk Assessment
94. Time Reduce exposure time
Job rotation
Work – rest regimes
Work scheduling
Distance Segregation
Restrict access
Rest areas
Organisation Reduce numbers exposed
Good working practice
Written procedures
“Permits to work”
Work practices / organisation