2. Threshold Limit Values ® (TLVs)
for heat stress are included in
the American Conference of
Governmental Industrial
Hygienists (ACGIH) TLV booklet
3. TLVs® are guidelines designed
for use by occupational
hygienists in making decisions
regarding safe levels of
exposure to various chemical
substances and physical agents
found in the workplace.
4. This flowchart summarises how
to apply the TLV’s. However. It’s
quite complex. We’ll go through
it step by step
5. General approach
Detailed Heat Strain
Screening
Analysis Monitoring
6. General approach
Detailed Heat Strain
Screening
Analysis Monitoring
8. Screening
NO Clothing
adjustment factors
available?
YES
9. TLV Clothing Corrections
Clothing Type WBGT Correction
Work clothes (long sleeve and pants) 0
Cloth (woven material) coveralls 0
Double layer woven clothing 3
SMS polypropylene coveralls 0.5
Polyolefin overalls 1
Limited use vapour-barrier overalls 11
10. Screening
NO Clothing
adjustment factors
available?
YES
If no clothing adjustment factors are
available, go straight to heat strain
(physiological) monitoring
11. Screening
NO Clothing
adjustment factors
available?
YES
This may be necessary, for
example, where chemical
protective suits are being worn
12. TLV Clothing Corrections
Clothing Type WBGT Correction
Work clothes (long sleeve and pants) 0
Cloth (woven material) coveralls 0
Double layer woven clothing 3
SMS polypropylene coveralls 0.5
Polyolefin overalls 1
Limited use vapour-barrier overalls 11
13. Screening
NO Clothing
adjustment factors
available?
YES
Are screening NO
criteria for Action
Limit exceeded?
YES
14. Work out the WBGT from the
results of environmental
measurements and apply the
clothing corrections
15. WBGT Index
No direct exposure to sunlight
WBGT = 0.7 tnwb + 0.3 tg
With direct exposure to sunlight
WBGT = 0.7 tnwb + 0.2 tg + 0.1 ta
17. ACGIH TLVs – Action Limit
Allocation of Workload
work in work Light Moderate Heavy V ery
cycle 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
18. To use this table you have to know
• the time spent working and resting
• the metabolic rate
19. Metabolic rate categories
Category Metabolic Examples
Rate (W)
Sitting
Rest 115
Sitting or standing
Light 180 Light hand / arm work
Walking
Moderate 300 Moderate lifting
Heavy materials handling
Heavy 415
Pick and shovel work
Very Heavy 520
20. ACGIH TLVs – Action Limit
Allocation of Workload
work in work Light Moderate Heavy V ery
cycle 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
21. So, for a job involving moderate
work where 75% of the time is spent
working and 25% resting
22. ACGIH TLVs – Action Limit
Allocation of Workload
work in work Light Moderate Heavy V ery
cycle 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
23. ACGIH TLVs – Action Limit
Allocation of Workload
work in work Light Moderate Heavy V ery
cycle 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
24. ACGIH TLVs – Action Limit
Allocation of Workload
work in work Light Moderate Heavy V ery
cycle 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
25. ACGIH TLVs – Action Limit
Allocation of Workload
work in work Light Moderate Heavy V ery
cycle 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
26. ACGIH TLVs – Action Limit
Allocation of Workload
work in work Light Moderate Heavy V ery
cycle 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
If the adjusted WBGT is below this value the Action Limit is not exceeded
27. Screening
NO Clothing
adjustment factors
available?
YES
Are screening NO
criteria for Action Low Risk
Limit exceeded?
YES
28. Screening
NO Clothing
adjustment factors
available?
YES
Are screening NO
Continue work
criteria for Action Low Risk
Monitor
Limit exceeded?
YES
29. Screening
NO Clothing
adjustment factors
available?
YES
Are screening NO
Continue work
criteria for Action Low Risk
Monitor
Limit exceeded?
YES
NO
If the Action Limit is
Are screening
exceeded then the WBGT
criteria for TLV
exceeded? value is compared with the
TLV criteria
YES
30. ACGIH TLVs – Screening TLV
Allocation of Workload
work in work Light Moderate Heavy V ery
cycle 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
31. Screening
NO Clothing
adjustment factors
available?
YES
Are screening NO
Continue work
criteria for Action Low Risk
Monitor
Limit exceeded?
YES
Are screening NO Implement
criteria for TLV general
exceeded? controls
YES
32. General Information, instruction & training
controls Regular drinks of water
Self regulation
Health screening and surveillance
Encourage reporting symptoms
Encourage healthy lifestyles
Monitoring
33. Screening
NO Clothing
adjustment factors
available?
YES
Are screening NO
Continue work
criteria for Action Low Risk
Monitor
Limit exceeded?
YES
Are screening NO Implement Continue work
criteria for TLV general Maintain controls
exceeded? controls Monitor
YES
34. Screening
NO Clothing
adjustment factors
available?
YES
Are screening NO
Continue work
criteria for Action Low Risk
Monitor
Limit exceeded?
YES
Are screening NO Implement Continue work
criteria for TLV general Maintain controls
exceeded? controls Monitor
YES
35. Detailed analysis
NO Are data available
for detailed
analysis?
YES
If the TLV is exceeded,
consider carrying out a
more detailed analysis
using a more sophisticated
method, such as the
Predicted Heat Strain
(PHS) index
36. Detailed analysis
NO Are data available
for detailed
analysis?
YES
NO
Action Limit
exceeded?
YES
37. The Action Limit referred to
here is that associated with the
index being used NOT the
ACGIH Action Limit
38. Detailed analysis
NO Are data available
for detailed
analysis?
YES
NO
Action Limit
exceeded?
YES
39. Detailed analysis
NO Are data available
for detailed
analysis?
YES
NO
Action Limit
Low Risk
exceeded?
YES
40. Detailed analysis
NO Are data available
for detailed
analysis?
YES
NO
Action Limit Continue work
Low Risk
exceeded? Monitor
YES
41. Detailed analysis
NO Are data available
for detailed
analysis?
YES
NO
Action Limit Continue work
Low Risk
exceeded? Monitor
YES
NO
TLV exceeded?
YES
42. The TLV referred to here is the
limit value associated with the
index being used NOT the
ACGIH Screening TLVs
43. Detailed analysis
NO Are data available
for detailed
analysis?
YES
NO
Action Limit Continue work
Low Risk
exceeded? Monitor
YES
NO
TLV exceeded?
YES
44. Detailed analysis
NO Are data available
for detailed
analysis?
YES
NO
Action Limit Continue work
Low Risk
exceeded? Monitor
YES
NO Implement
TLV exceeded? general
controls
YES
45. Detailed analysis
NO Are data available
for detailed
analysis?
YES
NO
Action Limit Continue work
Low Risk
exceeded? Monitor
YES
NO Implement Continue work
TLV exceeded? general Maintain controls
controls Monitor
YES
46. Heat strain monitoring
NO Implement Continue work
TLV exceeded? general Maintain controls
controls Monitor
YES
What if the TLV is exceeded?
47. Heat strain monitoring
NO Implement Continue work
TLV exceeded? general Maintain controls
controls Monitor
YES
Perform heat strain
(physiological)
monitoring
51. Heat strain monitoring
NO Implement Continue work
TLV exceeded? general Maintain controls
controls Monitor
YES
Perform heat strain
(physiological)
monitoring
Excessive heat NO
strain based on
monitoring?
YES
52. Guidelines for limiting Heat Strain
Factor Work should be discontinued if:
Heart rate (beats per minute) Greater than 180 minus age in years
Core temperature Greater than 38.5 0C (acclimatised)
Greater than 38.0 0C (unacclimatised)
Recovery heart rate 120
(beats per minute) (at one minute after peak work)
Other Symptoms of sudden and severe
fatigue, nausea, dizziness or
lightheadedness
53. Heat strain monitoring
NO Implement Continue work
TLV exceeded? general Maintain controls
controls Monitor
YES
Perform heat strain
(physiological)
monitoring
Excessive heat NO
strain based on
monitoring?
YES
54. Heat strain monitoring
NO Implement Continue work
TLV exceeded? general Maintain controls
controls Monitor
YES
Perform heat strain
(physiological)
monitoring
Excessive heat NO
strain based on
monitoring?
YES
Implement Job-
specific controls
55. Job-specific controls
Engineering controls
Administrative controls
Personal protective
equipment
56. Heat strain monitoring
NO Implement Continue work
TLV exceeded? general Maintain controls
controls Monitor
YES
Perform heat strain
(physiological)
monitoring
Excessive heat NO
strain based on
monitoring?
YES
Implement Job-
specific controls
57. Heat strain monitoring
NO Implement Continue work
TLV exceeded? general Maintain controls
controls Monitor
YES
Perform heat strain
(physiological)
monitoring
Excessive heat NO
strain based on
monitoring?
YES
Implement Job-
specific controls
58.
59.
60. At workstation
Ta = 24 0C
Tw = 22 0C
Tg = 28 0C
V = 0.4 m/s
Work involves monitoring process
Minimal manual effort required
Standard overalls worn
61. WBGT Index
No direct exposure to sunlight
WBGT = 0.7 tnwb + 0.3 tg
With direct exposure to sunlight
WBGT = 0.7 tnwb + 0.2 tg + 0.1 ta
62. At workstation
Ta = 24 0C
Tw = 22 0C
Tg = 28 0C
V = 0.4 m/s
WBGT = 23.8 0C
63. Screening
NO Clothing
adjustment factors
available?
YES
64. TLV Clothing Corrections
Clothing Type WBGT Correction
Work clothes (long sleeve and pants) 0
Cloth (woven material) coveralls 0
Double layer woven clothing 3
SMS polypropylene coveralls 0.5
Polyolefin overalls 1
Limited use vapour-barrier overalls 11
65. Screening
NO Clothing
adjustment factors
available?
YES
Are screening NO
criteria for Action
Limit exceeded?
YES
67. ACGIH TLVs – Action Limit
Allocation of Workload
work in work Light Moderate Heavy V ery
cycle 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
68. ACGIH TLVs – Action Limit
Allocation of Workload
work in work Light Moderate Heavy V ery
cycle 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
WBGT = 23.8 0C
69. Screening
NO Clothing
adjustment factors
available?
YES
Are screening NO
criteria for Action Low Risk
Limit exceeded?
YES
70. Screening
NO Clothing
adjustment factors
available?
YES
Are screening NO
Continue work
criteria for Action Low Risk
Monitor
Limit exceeded?
YES
71.
72. Boiler Cleaning
Air Wet Globe Air
temp. bulb temp. velocity
(0C) temp. (0C) (m/s)
(0C)
Start of work 34 19 51 0.2
After 5 hours 32.5 18.5 51.5 0.2
Heavy manual effort required
Standard overalls worn
73. Boiler Cleaning
Air Wet Globe Air
temp. bulb temp. velocity
(0C) temp. (0C) (m/s)
(0C)
Start of work 34 19 51 0.2
After 5 hours 32.5 18.5 51.5 0.2
WBGT = 28.6 0C
74. Screening
NO Clothing
adjustment factors
available?
YES
75. TLV Clothing Corrections
Clothing Type WBGT Correction
Work clothes (long sleeve and pants) 0
Cloth (woven material) coveralls 0
Double layer woven clothing 3
SMS polypropylene coveralls 0.5
Polyolefin overalls 1
Limited use vapour-barrier overalls 11
76. Screening
NO Clothing
adjustment factors
available?
YES
Are screening NO
criteria for Action
Limit exceeded?
YES
78. ACGIH TLVs – Action Limit
Allocation of Workload
work in work Light Moderate Heavy V ery
cycle 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
79. ACGIH TLVs – Action Limit
Allocation of Workload
work in work Light Moderate Heavy V ery
cycle 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
80. ACGIH TLVs – Action Limit
Allocation of Workload
work in work Light Moderate Heavy V ery
cycle 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
WBGT = 28.6 0C
So Action Limit is exceeded
81. Screening
NO Clothing
adjustment factors
available?
YES
Are screening
criteria for Action
Limit exceeded?
YES
Are screening NO
criteria for TLV
exceeded?
YES
82. ACGIH TLVs – Screening TLV
Allocation of Workload
work in work Light Moderate Heavy V ery
cycle 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
83. ACGIH TLVs – Screening TLV
Allocation of Workload
work in work Light Moderate Heavy V ery
cycle 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
WBGT = 28.6 0C
So TLV is NOT exceeded provided
work is restricted to 50% of shift
84. Screening
NO Clothing
adjustment factors
available?
YES
Are screening NO
Continue work
criteria for Action Low Risk
Monitor
Limit exceeded?
YES
Are screening NO Implement
criteria for TLV general
exceeded? controls
YES
92. Screening
NO Clothing
adjustment factors
available?
YES
Are screening NO
Continue work
criteria for Action Low Risk
Monitor
Limit exceeded?
YES
Are screening NO Implement Continue work
criteria for TLV general Maintain controls
exceeded? controls Monitor
YES
93.
94. Furnace Repair
Air Wet bulb Globe Air
temp. temp. temp. velocity
(0C) (0C) (0C) (m/s)
98 45 150 1
Heavy manual effort required
Thick, woollen clothing worn
101. ACGIH TLVs – Action Limit
Allocation of Workload
work in work Light Moderate Heavy V ery
cycle 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
102. ACGIH TLVs – Action Limit
Allocation of Workload
work in work Light Moderate Heavy V ery
cycle 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
Corrected WBGT = 79.5 0C
So Action Limit is exceeded
103. Screening
NO Clothing
adjustment factors
available?
YES
Are screening
criteria for Action
Limit exceeded?
YES
Are screening NO
criteria for TLV
exceeded?
YES
104. ACGIH TLVs – Screening TLV
Allocation of Workload
work in work Light Moderate Heavy V ery
cycle 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
105. ACGIH TLVs – Screening TLV
Allocation of Workload
work in work Light Moderate Heavy V ery
cycle 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
Corrected WBGT = 79.5 0C
So TLV is exceeded
106. Are screening
criteria for TLV
exceeded?
YES
NO Are data available
for detailed
analysis?
YES
Perform heat strain
(physiological) Detailed analysis
monitoring
108. Mike Slater, Diamond Environmental Ltd. (mike@diamondenv.co.uk)
This presentation is distributed under the Creative Commons
Attribution-NonCommercial-ShareAlike
UK:International Licence