TLVs for heat stress

Mike Slater

Threshold Limit Values ® (TLVs) for heat stress are included in the American Conference of Governmental Industrial Hygienists (ACGIH) TLV booklet

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.

This flowchart summarises how to apply the TLV’s. However. It’s quite complex. We’ll go through

it step by step

Screening Detailed Analysis

Heat Strain Monitoring

General approach

STOP Heat Stress expected?

NO

YES

SCREENING

Clothing adjustment factors

available?

YES

NO

Screening

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


available?

YES

NO

Screening

If no clothing adjustment factors are available, go straight to heat strain (physiological) monitoring


available?

YES

NO

Screening

This may be necessary, for example, where chemical protective suits are being worn


available?

Are screening criteria for Action Limit exceeded?

YES

YES

NO

NO

Screening

Work out the WBGT from the results of environmental measurements and apply the clothing corrections

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

Compare the corrected WBGT with the Action Limit Values

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

To use this table you have to know • the time spent working and resting • the metabolic rate

Metabolic rate categories

Category Metabolic Rate (W)

Examples

Rest 115 Sitting

Light 180 Sitting or standing Light hand / arm work

Moderate 300 Walking Moderate lifting

Heavy 415 Heavy materials handling

Very Heavy 520 Pick and shovel work



Workload


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

So, for a job involving moderate work where 75% of the time is spent working and 25% resting



Workload


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



Workload


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


available?


YES

YES

Low Risk

NO

NO

Screening


available?


YES

YES

Low Risk Continue work

Monitor

NO

NO

Screening


available?


Are screening criteria for TLV

exceeded?

YES

YES

YES


Monitor

NO

NO

NO

Screening

If the Action Limit is exceeded then the WBGT value is compared with the TLV criteria

ACGIH TLVs – Screening TLV


Workload


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


available?



exceeded?

YES

YES

YES


Monitor

Implement general controls

NO

NO

NO

Screening

General controls

Information, instruction & training

Regular drinks of water

Self regulation

Health screening and surveillance Encourage reporting symptoms

Encourage healthy lifestyles

Monitoring


available?



exceeded?

YES

YES

YES


Monitor


Continue work Maintain controls

Monitor

NO

NO

NO

Screening

Are data available for detailed

analysis?

YES

NO

Detailed analysis

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


analysis?

Action Limit exceeded?

YES

YES

NO

NO

Detailed analysis

The Action Limit referred to here is that associated with the index being used NOT the ACGIH Action Limit


analysis?


YES

YES

NO

NO

Detailed analysis


analysis?


YES

YES

Low Risk

NO

NO

Detailed analysis


analysis?


YES

YES


Monitor

NO

NO

Detailed analysis


analysis?


TLV exceeded?

YES

YES

YES


Monitor

NO

NO

NO

Detailed analysis

The TLV referred to here is the limit value associated with the index being used NOT the ACGIH Screening TLVs


analysis?


TLV exceeded?

YES

YES

YES


Monitor

NO

NO

NO

Detailed analysis


analysis?


TLV exceeded?

YES

YES

YES


Monitor


NO

NO

NO

Detailed analysis


analysis?


TLV exceeded?

YES

YES

YES


Monitor



Monitor

NO

NO

NO

Detailed analysis

TLV exceeded?

YES



Monitor

NO

Heat strain monitoring

What if the TLV is exceeded?

TLV exceeded?

YES



Monitor

NO


Perform heat strain (physiological)

monitoring

Physiological assessment

Core Temperature Heart rate

Personal Monitor

Miner’s Core Temperature & Heart Rate

Source: OHTA.

TLV exceeded?

Excessive heat strain based on

monitoring?

YES

YES



Monitor

NO

NO



monitoring

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 (beats per minute)

120 (at one minute after peak work)

Other Symptoms of sudden and severe fatigue, nausea, dizziness or lightheadedness

TLV exceeded?


monitoring?

YES

YES



Monitor

NO

NO



monitoring

TLV exceeded?


monitoring?

YES

YES



Monitor

NO

NO



monitoring

Implement Job-specific controls

Job-specific controls

Engineering controls

Administrative controls

Personal protective equipment

TLV exceeded?


monitoring?

YES

YES



Monitor

NO

NO



monitoring

Implement Job-specific controls

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

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

At workstation Ta = 24 0C

Tw = 22 0C

Tg = 28 0C

V = 0.4 m/s

WBGT = 23.8 0C


available?

YES

NO

Screening


available?


YES

YES

NO

NO

Screening



Rest 115

Light 180

Moderate 300

Heavy 415

Very Heavy 520



Workload


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



Workload


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


available?


YES

YES

Low Risk

NO

NO

Screening


available?


YES

YES


Monitor

NO

NO

Screening

Boiler Cleaning

Air

temp.

(0C)

Wet

bulb

temp.

(0C)

Globe

temp.

(0C)

Air

velocity

(m/s)

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

Air

temp.

(0C)

Wet

bulb

temp.

(0C)

Globe

temp.

(0C)

Air

velocity

(m/s)

Start of work 34 19 51 0.2

After 5 hours 32.5 18.5 51.5 0.2

WBGT = 28.6 0C

Boiler Cleaning


available?

YES

NO

Screening


available?


YES

YES

NO

NO

Screening



Rest 115

Light 180

Moderate 300

Heavy 415

Very Heavy 520



Workload


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



Workload


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


available?



exceeded?

YES

YES

YES

NO

NO

Screening



Workload


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



Workload


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


available?



exceeded?

YES

YES

YES


Monitor


NO

NO

NO

Screening

Reduce risk

Allow boiler to cool down before starting work

Working methods

Mechanical aids

Self pacing

Manage exposure time

Implement work:rest regime

Work restricted to 25% to 50% of work cycle

Provide information, instruction and training

Risks

Good working practice

Symptoms to look out for

Provide water

Drink at regular intervals

Health surveillance

Pre-placement medical screening

Regular health checks

Encourage reporting of symptoms

Encourage healthy lifestyle

Diet

Exercise

Moderate alcohol consumption


available?



exceeded?

YES

YES

YES


Monitor



Monitor

NO

NO

NO

Screening

Furnace Repair

Air

temp.

(0C)

Wet bulb

temp.

(0C)

Globe

temp.

(0C)

Air

velocity

(m/s)

98 45 150 1

Heavy manual effort required Thick, woollen clothing worn

Furnace Repair

Air

temp.

(0C)

Wet bulb

temp.

(0C)

Globe

temp.

(0C)

Air

velocity

(m/s)

98 45 150 1

WBGT = 76.5 0C

Furnace Repair

Air

temp.

(0C)

Wet bulb

temp.

(0C)

Globe

temp.

(0C)

Air

velocity

(m/s)

98 45 150 1

Corrected WBGT = 79.5 0C


available?


YES

YES

NO

NO

Screening



Rest 115

Light 180

Moderate 300

Heavy 415

Very Heavy 520



Workload


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



Workload


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


available?



exceeded?

YES

YES

YES

NO

NO

Screening



Workload


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



Workload


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 Corrected WBGT = 79.5 0C So TLV is exceeded


analysis?

YES

NO


exceeded?

YES

Detailed analysis Perform heat strain

(physiological) monitoring

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Mike Slater

Mike Slater, Diamond Environmental Ltd. ([email protected])

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TLVs for heat stress

Health & Medicine

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