Annex III of NR9 – Heat

(MTP Ordinance no. 426, of September 7, 2021)


  1. Objectives
  2. Scope
  3. Responsibilities of the organization
  4. Preventive measures
  5. Acclimatization
  6. Emergency procedures
  7. Objectives

1.1 To establish the requirements for assessing occupational exposure to heat, when identified in the Risk Management Program (RMP), provided for in NR-01, and to support the implementation of prevention measures.

  1. Scope

2.1 The provisions set out in this Annex shall apply to occupational exposure to the physical agent of heat.

  1. Responsibilities of the organization

3.1 The organization shall take preventive measures to ensure that occupational exposure to heat does not have an adverse effect on the health of workers.

3.1.1 The organization shall provide workers with specific guidance on:

a) factors affecting the risks associated with exposure to heat
b) heat-related disorders, with examples of their signs and symptoms, treatment, etc;
c) the need to report the occurrence of heat-related signs and symptoms to a supervisor or doctor;
d) preventive measures related to exposure to heat, in accordance with the risk assessment of the activity;
e) information about the working environment and its characteristics; and
f) emergency situations arising from occupational exposure to heat and the action to be taken.

3.1.2 Specific annual periodic training shall be provided when indicated in the preventive measures.

3.2 The preliminary assessment of occupational exposure to heat shall take into account the following aspects, as appropriate:

a) identification of the hazard;
b) characterization of the sources of generation;
c) identification of the possible pathways and means of propagation of the agents in the work environment;
d) identification of the functions and determination of the number of exposed workers;
e) characterize the activities and the type of exposure, taking into account the organization of work;
f) identify existing data in the enterprise indicating possible health effects as a result of work;
g) possible injuries or health problems related to the identified hazards that are available in the technical literature;
h) a description of existing preventive measures;
i) characteristics of environmental factors and other working conditions that may affect heat exposure and the mechanism of heat exchange between the worker and the environment;
j) estimates of the time spent in each activity and thermal situation to which the worker is exposed during the working day;
k) the metabolic rate for performing activities involving heat exposure; and
i) available records of occupational exposure to heat.

3.2.1 The preliminary assessment shall support the adoption of preventive measures, without prejudice to other measures provided for in other NRs. If the information obtained in the preliminary assessment is not sufficient to allow a decision to be taken on the need to implement prevention measures, a quantitative assessment shall be carried out to:

a) demonstrate control of exposure or the absence of risks identified in the preliminary assessment;
b) measure the exposure of workers;
c) support the development of preventive measures.

3.3 The quantitative assessment of heat shall be carried out on the basis of the methodology and procedures described in the Occupational Hygiene Standard No. 06 (NHO 06) (2nd edition – 2017) of Fundacentro, in the following aspects:

a) determination of thermal overload by means of the IBUTG index – Globe Thermometer Wet Bulb Index;
b) measurement devices and methods of placement, positioning and procedures for their use in the evaluated locations;
c) procedures for the conduct of the operator; and
d) measurements and calculations.

3.3.1 The metabolic rate shall be estimated by comparing the activity performed by the worker with the options presented in Table 3 of this Annex. If a specific activity is not shown in Table 3 of this Annex, the value of the metabolic rate shall be obtained by association with a similar activity in that Table. If classification by similarity is not possible, the metabolic rate may be estimated from other technical references, provided they are technically justified.

3.3.2 For outdoor activities without artificial heat sources, a Fundacentro tool, if available, may be used to estimate the IBUTG as an alternative to the provisions of items 3.3 (b), (c) and (d).

  1. Preventive measures

4.1 Preventive measures

4.1.1 Whenever the action levels for occupational exposure to heat set out in Table 1 are exceeded, the organization shall take one or more of the following measures:

a) provide and encourage the consumption of fresh drinking water (or other suitable replacement fluid); and
b) schedule the heaviest work (above 414 W – four hundred and fourteen watts), preferably during periods of milder thermal conditions, provided that these periods do not pose additional risks.

4.1.2 For enclosed environments or those with artificial heat sources, in addition to 4.1.1, the employer shall provide work clothing appropriate to the type of exposure and the nature of the activity.

4.2 Corrective measures

4.2.1 The aim of corrective measures is to reduce occupational exposure to heat below the exposure limit value.

4.2.2 If the exposure limits set out in Table 2 are exceeded, the organization shall take one or more of the following corrective measures:

a) adjust work processes, routines or operations;
b) alternate activities that result in exposure to higher levels of heat with other activities that do not result in exposure or that result in exposure at lower levels, thereby reducing exposure; and
c) provide access to places, including natural places, that are thermally milder, that allow spontaneous breaks, and that allow for thermal recovery in activities performed in open areas and away from any buildings or natural or artificial structures. For enclosed environments or those with artificial heat sources, in addition to 4.2.2, the organization must

a) adjust workplaces and workstations
b) reduce the temperature or emission of heat sources;
c) use radiant heat barriers
d) adjust the ventilation system; and
e) adjust the temperature and relative humidity of the air.

4.2.3 The occupational health screening program (PCMSO) provided for in Regulatory Standard No. 07 shall include medical procedures and evaluations, taking into account the need for complementary examinations and physiological monitoring, when the exposure limit values provided for in Table 2 of this Annex are exceeded and the risk of thermal and physiological overload of workers exposed to heat is characterized. The risk of thermal and physiological overload with the possibility of serious injury to the physical integrity or health of workers shall be identified:

a) if the measures provided for in item 4 of this Annex are not adopted; or
b) if the measures taken are not sufficient to reduce the risk.

  1. Acclimatization

5.1 For occupational exposure to heat above the action level, worker acclimatization as described in the PCMSO shall be considered.

5.2 If it is necessary to draw up an acclimatization plan for workers, the parameters set out in Fundacentro’s NHO 06 or other technical references issued by a competent organization shall be taken into account.

  1. Emergency procedures

6.1 The organization shall have a specific heat emergency procedure, including

a) the means and resources necessary to provide first aid or refer workers for medical care; and
b) information for all people involved in emergency scenarios.

Table 1 – Action level for acclimatized workers

Table 1 – Action level for acclimatized workers

Table 2 – Occupational exposure limit to heat for acclimatized workers

Table 2 – Occupational exposure limit to heat for acclimatized workers

Note 1: The limits established are valid only for workers wearing clothing that does not increase the average IBUTG in accordance with the corrections provided in Table 4 of this Annex.

Note 2: The limits apply to workers who are fit for work as determined by the medical assessment provided in NR-07.

Table 3 – Metabolic rate by type of activity

ActivityMetabolic rate (W)
Light work with hands126
Moderate work with hands153
Heavy work with hands171
Light work with one arm162
Moderate work with one arm198
Heavy work with one arm234
Light work with two arms216
Moderate work with two arms252
Heavy work with two arms288
Light work with arms and legs324
Moderate work with arms and legs441
Heavy work with arms and legs603
Standing, squatting or kneeling
At rest126
Light work with the hands153
Moderate work with the hands180
Heavy work with the hands198
Light work with one arm189
Moderate work with one arm225
Heavy work with one arm261
Light work with two arms243
Moderate work with two arms279
Heavy work with two arms315
Light work with the body351
Moderate work with the body468
Heavy work with the body630
Standing, moving
Walking on the level ground
1. Without load
2 km/h198
3 km/h252
4 km/h297
5 km/h360
2. With load
10 kg, 4 km/h333
30 kg, 4 km/h450
Running on the level ground
9 km/h787
12 km/h873
15 km/h990
Going up a ramp
1. Without load
at 5° incline, 4 km/h324
at 15° incline, 3 km/h378
at 25° incline, 3 km/h540
2. With 20 kg load
at 15° incline, 4 km/h486
at 25° incline, 4 km/h738
Going down a ramp (5 km/h) without load
at 5° incline243
at 15° incline252
at 25° incline324
Climbing stairs (80 steps per minute – step height of 0.17 m)
without load522
with load (20 kg)648
Descending stair (80 steps per minute – step height of 0.17 m)
without load279
with load (20 kg)400
Moderate arm work (e.g sweeping, warehouse work)320
Moderate lifting or pushing349
Pushing wheelbarrows on the same level with a load391
Carrying weights or vigorous arm movements (e.g. working with a scythe)495
Heavy lifting, pushing or pulling (e.g. shovelling, digging)524
Table 3 – Metabolic rate by type of activity

Table 4 – Average IBUTG Adjustment Increments for Some Types of Clothing*

Type of ClothingAddition to IBUTG [°C]
Work uniform (trousers and long-sleeved shirt)0
Fabric coveralls0
SMS (Spun-Melt-Spun) polypropylene coveralls0.5
Polyolefin coveralls2
Lined coveralls or jumpsuits3
Steamproof long sleeve apron4
Steamproof lined coveralls10
Steamproof lined coveralls over work clothes12
Table 4 – Average IBUTG Adjustment Increments for Some Types of Clothing

*The IBUTG value for clothing with a hood should be increased by 1 °C.