Thursday, 27 October 2011 19:47

## Case Study: Heat Indices: Formulae and Definitions

Written by
Rate this item
(1 Vote)

I. Index of thermal stress (ITS)

The improved heat balance equation is:

where  is the evaporation required to maintain heat balance,  is the solar load, and metabolic heat production H is used instead of metabolic rate to account for external work. An important improvement is the recognition that not all sweat evaporates (e.g., some drips) hence required sweat rate is related to required evaporation rate by:

where nsc is the efficiency of sweating.

Used indoors, sensible heat transfer is calculated from:

For outdoor conditions with solar load,  is replaced with  and allowance made for solar load (RS ) by:

The equations used are fits to experimental data and are not strictly rational.

Maximum evaporation heat loss is:

and efficiency of sweating is given by:

but

nsc = 1, если

and

nsc = 0.29, если

The index of thermal stress (ITS) in g/h is given by:

where  is the required evaporation rate , 0.37 converts  into g/h andnsc is the efficiency of sweating (McIntyre 1980).

II. Required sweat rate

Similar to the other rational indices,  is derived from the six basic parameters (air temperature (), radiant temperature ( ), relative humidity air velocity (v), clothing insulation ( ), metabolic rate (M) and external work (W)). Effective radiation area values for posture (sitting = 0.72, standing = 0.77) are also required. From this the evaporation required is calculated from:

Equations are provided for each component (see table 8 and table 9). Mean skin temperature is calculated from a multiple linear regression equation or a value of 36°C is assumed.

From the required evaporation (Ereg) and maximum evaporation (Emax) and sweating efficiency (r), the following are calculated:

Required skin wettedness

Required sweat rate

III. Predicted 4-hour sweat rate (P4SR)

Steps taken to obtain the P4SR index value are summarized by McIntyre (1980) as follows:

If , increase wet bulb temperature by .

If the metabolic rate M > 63 , increase wet bulb temperature by the amount   indicated in the chart (see figure 6).

If the men are clothed, increase the wet bulb temperature by .

The (P4SR) is determined from figure 6. The P4SR is then:

IV. Heart rate

where M is metabolic rate,  is air temperature in °C and Pa is vapour pressure in Mb.

Givoni and Goldman (1973) provide equations for predicting heart rate of persons (soldiers) in hot environments. They define an index for heart rate (IHR) from a modification of predicted equilibrium rectal temperature,

IHR is then:

where M = metabolic rate (watts), = mechanical work (watts), clo = thermal insulation of clothing,  = air temperature = total metabolic and environmental heat load (watts),  = evaporative cooling capacity for clothing and environment (watts).

The equilibrium heart rate (in beats per minute) is then given by:

for IHR 225

that is, a linear relationship (between rectal temperature and heart rate) for heart rates up to about 150 beats per minute. For IHR >225:

that is, an exponential relationship as heart rate approaches maximum, where:

= equilibrium heart rate (bpm),

65 = assumed resting heart rate in comfortable conditions (bpm), and t = time in hours.

V. Wet bulb globe temperature index (WBGT)

Wet bulb globe temperature is given by:

for conditions with solar radiation, and:

for indoor conditions with no solar radiation, where  Tnwb= temperature of a naturally ventilated wet bulb thermometer, Ta = air temperature, and  Tg = temperature of a 150 mm diameter black globe thermometer.

Back

### Latest from April Weber

" DISCLAIMER: The ILO does not take responsibility for content presented on this web portal that is presented in any language other than English, which is the language used for the initial production and peer-review of original content. Certain statistics have not been updated since the production of the 4th edition of the Encyclopaedia (1998)."

## Contents

Part I. The Body
Part II. Health Care
Part III. Management & Policy
Part IV. Tools and Approaches
Part V. Psychosocial and Organizational Factors
Part VI. General Hazards
Part VII. The Environment
Part VIII. Accidents and Safety Management
Part IX. Chemicals
Part X. Industries Based on Biological Resources
Part XI. Industries Based on Natural Resources
Part XII. Chemical Industries
Part XIII. Manufacturing Industries
Part XIV. Textile and Apparel Industries
Part XV. Transport Industries
Part XVI. Construction
Part XVIII. Guides

## Heat and Cold References

ACGIH (American Conference of Governmental Industrial Hygienists). 1990. Threshold Limit Values and Biological Exposure Indices for 1989–1990. New York: ACGIH.

—. 1992. Cold stress. In Threshold Limit Values for Physical Agents in the Work Environment. New York: ACGIH.

Bedford, T. 1940. Environmental warmth and its measurement. Medical Research Memorandum No. 17. London: Her Majesty’s Stationery Office.

Belding, HS and TF Hatch. 1955. Index for evaluating heat stress in terms of resulting physiological strain. Heating Piping Air Condit 27:129–136.

Bittel, JHM. 1987. Heat debt as an index for cold adaptation in men. J Appl Physiol 62(4):1627–1634.

Bittel, JHM, C Nonotte-Varly, GH Livecchi-Gonnot, GLM Savourey and AM Hanniquet. 1988. Physical fitness and thermoregulatory reactions in a cold environment in men. J Appl Physiol 65:1984-1989.

Bittel, JHM, GH Livecchi-Gonnot, AM Hanniquet and JL Etienne. 1989. Thermal changes observed before and after J.L. Etienne’s journey to the North Pole. Eur J Appl Physiol 58:646–651.

Bligh, J and KG Johnson. 1973. Glossary of terms for thermal physiology. J Appl Physiol 35(6):941–961.

Botsford, JH. 1971. A wet globe thermometer for environmental heat measurement. Am Ind Hyg J 32:1–10.

Boutelier, C. 1979. Survie et protection des équipages en cas d’immersion accidentelle en eau froide. Neuilly-sur-Seine: AGARD A.G. 211.

Brouha, L. 1960. Physiology in Industry. New York: Pergamon Press.

Burton, AC and OG Edholm. 1955. Man in a Cold Environment. London: Edward Arnold.

Chen, F, H Nilsson and RI Holmér. 1994. Cooling responses of finger pad in contact with an aluminum surface. Am Ind Hyg Assoc J 55(3):218-22.

Comité Européen de Normalisation (CEN). 1992. EN 344. Protective Clothing Against Cold. Brussels: CEN.

—. 1993. EN 511. Protective Gloves Against Cold. Brussels: CEN.

Commission of the European Communities (CEC). 1988. Proceedings of a seminar on heat stress indices. Luxembourg: CEC, Health and Safety Directorate.

Daanen, HAM. 1993. Deterioration of manual performance in cold and windy conditions. AGARD, NATO, CP-540.

Dasler, AR. 1974. Ventilation and thermal stress, ashore and afloat. In Chapter 3, Manual of Naval Preventive Medicine. Washington, DC: Navy Department, Bureau of Medicine and Surgery.

—. 1977. Heat stress, work functions and physiological heat exposure limits in man. In Thermal Analysis—Human Comfort—Indoor Environments. NBS Special Publication 491. Washington, DC: US Department of Commerce.

Deutsches Institut für Normierung (DIN) 7943-2. 1992. Schlafsacke, Thermophysiologische Prufung. Berlin: DIN.

Dubois, D and EF Dubois. 1916. Clinical calorimetry X: A formula to estimate the appropiate surface area if height and weight be known. Arch Int Med 17:863–871.

Eagan, CJ. 1963. Introduction and terminology. Fed Proc 22:930–933.

Edwards, JSA, DE Roberts, and SH Mutter. 1992. Relations for use in a cold environment. J Wildlife Med 3:27–47.

Enander, A. 1987. Sensory reactions and performance in moderate cold. Doctoral thesis. Solna: National Institute of Occupational Health.

Fuller, FH and L Brouha. 1966. New engineering methods for evaluating the job environment. ASHRAE J 8(1):39–52.

Fuller, FH and PE Smith. 1980. The effectiveness of preventive work procedures in a hot workshop. In FN Dukes-Dobos and A Henschel (eds.). Proceedings of a NIOSH Workshop on Recommended Heat Stress Standards. Washington DC: DHSS (NIOSH) publication No. 81-108.

—. 1981. Evaluation of heat stress in a hot workshop by physiological measurements. Am Ind Hyg Assoc J 42:32–37.

Gagge, AP, AP Fobelets and LG Berglund. 1986. A standard predictive index of human response to the thermal environment. ASHRAE Trans 92:709–731.

Gisolfi, CV and CB Wenger. 1984. Temperature regulation during exercise: Old concepts, new ideas. Exercise Sport Sci Rev 12:339–372.

Givoni, B. 1963. A new method for evaluating industrial heat exposure and maximum permissible work load. Paper submitted to the International Biometeorological Congress in Paris, France, September 1963.

—. 1976. Man, Climate and Architecture, 2nd ed. London: Applied Science.

Givoni, B and RF Goldman. 1972. Predicting rectal temperature response to work, environment and clothing. J Appl Physiol 2(6):812–822.

—. 1973. Predicting heart rate response to work, environment and clothing. J Appl Physiol 34(2):201–204.

Goldman, RF. 1988. Standards for human exposure to heat. In Environmental Ergonomics, edited by IB Mekjavic, EW Banister and JB Morrison. London: Taylor & Francis.

Hales, JRS and DAB Richards. 1987. Heat Stress. Amsterdam, New York: Oxford Excerpta Medica.

Hammel, HT. 1963. Summary of comparative thermal patterns in man. Fed Proc 22:846–847.

Havenith, G, R Heus and WA Lotens. 1990. Clothing ventilation, vapour resistance and permeability index: Changes due to posture, movement and wind. Ergonomics 33:989–1005.

Hayes. 1988. In Environmental Ergonomics, edited by IB Mekjavic, EW Banister and JB Morrison. London: Taylor & Francis.

Holmér, I. 1988. Assessment of cold stress in terms of required clothing insulation—IREQ. Int J Ind Erg 3:159–166.

—. 1993. Work in the cold. Review of methods for assessment of cold stress. Int Arch Occ Env Health 65:147–155.

—. 1994. Cold stress: Part 1—Guidelines for the practitioner. Int J Ind Erg 14:1–10.

—. 1994. Cold stress: Part 2—The scientific basis (knowledge base) for the guide. Int J Ind Erg 14:1–9.

Houghton, FC and CP Yagoglou. 1923. Determining equal comfort lines. J ASHVE 29:165–176.

International Organization for Standardization (ISO). 1985. ISO 7726. Thermal Environments—Instruments and Methods for Measuring Physical Quantities. Geneva: ISO.

—. 1989a. ISO 7243. Hot Environments—Estimation of the Heat Stress on Working Man, Based on the WBGT Index (Wet Bulb Globe Temperature). Geneva: ISO.

—. 1989b. ISO 7933. Hot Environments—Analytical Determination and Interpretation of Thermal Stress using Calculation of Required Sweat Rate. Geneva: ISO.

—. 1989c. ISO DIS 9886. Ergonomics—Evaluation of Thermal Strain by Physiological Measurements. Geneva: ISO.

—. 1990. ISO 8996. Ergonomics—Determination of Metabolic Heat Production. Geneva: ISO.

—. 1992. ISO 9886. Evaluation of Thermal Strain by Physiological Measurements. Geneva: ISO.

—. 1993. Assessment of the Influence of the Thermal Environment using Subjective Judgement Scales. Geneva: ISO.

—. 1993. ISO CD 12894. Ergonomics of the Thermal Environment—Medical Supervision of Individuals Exposed to Hot or Cold Environments. Geneva: ISO.

—. 1993. ISO TR 11079 Evaluation of Cold Environments—Determination of Required Clothing Insulation, IREQ. Geneva: ISO. (Technical Report)

—. 1994. ISO 9920. Ergonomics—Estimation of the Thermal Characteristics of a Clothing Ensemble. Geneva: ISO.

—. 1994. ISO 7730. Moderate Thermal Environments—Determination of the PMV and PPD Indices and Specification of the Conditions for Thermal Comfort. Geneva: ISO.

—. 1995. ISO DIS 11933. Ergonomics of the Thermal Environment. Principles and Application of International Standards. Geneva: ISO.

Kenneth, W, P Sathasivam, AL Vallerand and TB Graham. 1990. Influence of caffeine on metabolic responses of men at rest in 28 and 5C. J Appl Physiol 68(5):1889–1895.

Kenney, WL and SR Fowler. 1988. Methylcholine-activated eccrine sweat gland density and output as a function of age. J Appl Physiol 65:1082–1086.

Kerslake, DMcK. 1972. The Stress of Hot Environments. Cambridge: Cambridge University Press.

LeBlanc, J. 1975. Man in the Cold. Springfield, IL, US: Charles C Thomas Publ.

Leithead, CA and AR Lind. 1964. Heat Stress and Head Disorders. London: Cassell.

Lind, AR. 1957. A physiological criterion for setting thermal environmental limits for everybody’s work. J Appl Physiol 18:51–56.

Lotens, WA. 1989. The actual insulation of multilayer clothing. Scand J Work Environ Health 15 Suppl. 1:66–75.

—. 1993. Heat transfer from humans wearing clothing. Thesis, Technical University. Delft, Netherlands. (ISBN 90-6743-231-8).

Lotens, WA and G Havenith. 1991. Calculation of clothing insulation and vapour resistance. Ergonomics 34:233–254.

Maclean, D and D Emslie-Smith. 1977. Accidental Hypothermia. Oxford, London, Edinburgh, Melbourne: Blackwell Scientific Publication.

Macpherson, RK. 1960. Physiological responses to hot environments. Medical Research Council Special Report Series No. 298. London: HMSO.

Martineau, L and I Jacob. 1988. Muscle glycogen utilization during shivering thermogenesis in humans. J Appl Physiol 56:2046–2050.

Maughan, RJ. 1991. Fluid and electrolyte loss and replacement in exercise. J Sport Sci 9:117–142.

McArdle, B, W Dunham, HE Halling, WSS Ladell, JW Scalt, ML Thomson and JS Weiner. 1947. The prediction of the physiological effects of warm and hot environments. Medical Research Council Rep 47/391. London: RNP.

McCullough, EA, BW Jones and PEJ Huck. 1985. A comprehensive database for estimating clothing insulation. ASHRAE Trans 91:29–47.

McCullough, EA, BW Jones and T Tamura. 1989. A database for determining the evaporative resistance of clothing. ASHRAE Trans 95:316–328.

McIntyre, DA. 1980. Indoor Climate. London: Applied Science Publishers Ltd.

Mekjavic, IB, EW Banister and JB Morrison (eds.). 1988. Environmental Ergonomics. Philadelphia: Taylor & Francis.

Nielsen, B. 1984. Dehydration, rehydration and thermoregulation. In E Jokl and M Hebbelinck (eds.). Medicine and Sports Science. Basel: S. Karger.

—. 1994. Heat stress and acclimation. Ergonomics 37(1):49–58.

Nielsen, R, BW Olesen and P-O Fanger. 1985. Effect of physical activity and air velocity on the thermal insulation of clothing. Ergonomics 28:1617–1632.

National Institute for Occupational Safety and Health (NIOSH). 1972. Occupational exposure to hot environments. HSM 72-10269. Washington, DC: US Department of Health Education and Welfare.

—. 1986. Occupational exposure to hot environments. NIOSH Publication No. 86-113. Washington, DC: NIOSH.

Nishi, Y and AP Gagge. 1977. Effective temperature scale used for hypo- and hyperbaric environments. Aviation Space and Envir Med 48:97–107.

Olesen, BW. 1985. Heat stress. In Bruel and Kjaer Technical Review No. 2. Denmark: Bruel and Kjaer.

Olesen, BW, E Sliwinska, TL Madsen and P-O Fanger. 1982. Effect of body posture and activity on the thermal insulation of clothing: Measurements by a movable thermal manikin. ASHRAE Trans 88:791–805.

Pandolf, KB, BS Cadarette, MN Sawka, AJ Young, RP Francesconi and RR Gonzales. 1988. J Appl Physiol 65(1):65–71.

Parsons, KC. 1993. Human Thermal Environments. Hampshire, UK: Taylor & Francis.

Reed, HL, D Brice, KMM Shakir, KD Burman, MM D’Alesandro and JT O’Brian. 1990. Decreased free fraction of thyroid hormones after prolonged Antarctic residence. J Appl Physiol 69:1467–1472.

Rowell, LB. 1983. Cardiovascular aspects of human thermoregulation. Circ Res 52:367–379.

—. 1986. Human Circulation Regulation During Physical Stress. Oxford: OUP.

Sato, K and F Sato. 1983. Individual variations in structure and function of human eccrine sweat gland. Am J Physiol 245:R203–R208.

Savourey, G, AL Vallerand and J Bittel. 1992. General and local adaptation after a ski journey in a severe arctic environment. Eur J Appl Physiol 64:99–105.

Savourey, G, JP Caravel, B Barnavol and J Bittel. 1994. Thyroid hormone changes in a cold air environment after local cold acclimation. J Appl Physiol 76(5):1963–1967.

Savourey, G, B Barnavol, JP Caravel, C Feuerstein and J Bittel. 1996. Hypothermic general cold adaptation induced by local cold acclimation. Eur J Appl Physiol 73:237–244.

Vallerand, AL, I Jacob and MF Kavanagh. 1989. Mechanism of enhanced cold tolerance by an ephedrine/caffeine mixture in humans. J Appl Physiol 67:438–444.

van Dilla, MA, R Day and PA Siple. 1949. Special problems of the hands. In Physiology of Heat Regulation, edited by R Newburgh. Philadelphia: Saunders.

Vellar, OD. 1969. Nutrient Losses through Sweating. Oslo: Universitetsforlaget.

Vogt, JJ, V Candas, JP Libert and F Daull. 1981. Required sweat rate as an index of thermal strain in industry. In Bioengineering, Thermal Physiology and Comfort, edited by K Cena and JA Clark. Amsterdam: Elsevier. 99–110.

Wang, LCH, SFP Man and AN Bel Castro. 1987. Metabolic and hormonal responses in theophylline-increased cold resistance in males. J Appl Physiol 63:589–596.

World Health Organization (WHO). 1969. Health factors involved in working under conditions of heat stress. Technical Report 412. Geneva: WHO.

Wissler, EH. 1988. A review of human thermal models. In Environmental Ergonomics, edited by IB Mekjavic, EW Banister and JB Morrison. London: Taylor & Francis.

Woodcock, AH. 1962. Moisture transfer in textile systems. Part I. Textile Res J 32:628–633.

Yaglou, CP and D Minard. 1957. Control of heat casualties at military training centers. Am Med Assoc Arch Ind Health 16:302–316 and 405.