ISO-7933-2004 Ergonmics of the thermal environment-Analytical determination and interpretation of heat stress using calculation of the predicted heat strain.pdf

Reference number ISO 7933:2004(E) © ISO 2004 INTERNATIONAL STANDARD ISO 7933 Second edition 2004-08-15 Ergonomics of the thermal environment Analytical determination and interpretation of heat stress using calculation of the predicted heat strain Ergonomie des ambiances thermiques Détermination analytique et interprétation de la contrainte thermique fondées sur le calcul de l'astreinte thermique prévisible Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=Aramco HQ/9980755100 Not for Resale, 04/11/2007 04:37:11 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 7933:2004(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat accepts no liability in this area. Adobe is a trademark of Adobe Systems Incorporated. Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below. © ISO 2004 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO's member body in the country of the requester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ii © ISO 2004 All rights reserved Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=Aramco HQ/9980755100 Not for Resale, 04/11/2007 04:37:11 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 7933:2004(E) © ISO 2004 All rights reserved iii Contents Page Forewordiv Introduction v 1 Scope1 2 Normative references .1 3 Symbols .2 4 Principles of the method of evaluation.5 5 Main steps of the calculation.5 5.1 General heat balance equation5 5.2 Calculation of the required evaporative heat flow, the required skin wettedness and the required sweat rate .7 6 Interpretation of required sweat rate 8 6.1 Basis of the method of interpretation.8 6.2 Analysis of the work situation.8 6.3 Determination of maximum allowable exposure time (Dlim).9 6.4 Organization of work in the heat .9 Annex A (normative) Data necessary for the computation of thermal balance.10 Annex B (informative) Criteria for estimating acceptable exposure time in a hot work environment.18 Annex C (informative) Metabolic rate .20 Annex D (informative) Clothing thermal characteristics 22 Annex E (informative) Computer programme for the computation of the Predicted Heat Strain Model24 Annex F (normative) Examples of the Predicted Heat Strain Model computations33 Bibliography .34 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=Aramco HQ/9980755100 Not for Resale, 04/11/2007 04:37:11 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 7933:2004(E) iv © ISO 2004 All rights reserved Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 7933 was prepared by Technical Committee ISO/TC 159, Ergonomics, Subcommittee SC 5, Ergonomics of the physical environment. This second edition cancels and replaces the first edition (ISO 7933:1989), which was based on the Required Sweat Rate index. In order to avoid any confusion and, as extensive modifications are brought to the prediction model, the name of the index has been changed to Predicted Heat Strain (PHS). Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=Aramco HQ/9980755100 Not for Resale, 04/11/2007 04:37:11 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 7933:2004(E) © ISO 2004 All rights reserved v Introduction Other International Standards of this series describe how the parameters influencing the human thermoregulation in a given environment must be estimated or quantified. Others specify how these parameters must be integrated in order to predict the degree of discomfort or the health risk in these environments. The present document was prepared to standardize the methods that occupational health specialists should use to approach a given problem and progressively collect the information needed to control or prevent the problem. The method of computation and interpretation of thermal balance is based on the latest scientific information. Future improvements concerning the calculation of the different terms of the heat balance equation, or its interpretation, will be taken into account when they become available. In its present form, this method of assessment is not applicable to cases where special protective clothing (reflective clothing, active cooling and ventilation, impermeable, with personal protective equipment) is worn. In addition, occupational health specialists are responsible for evaluating the risk encountered by a given individual, taking into consideration his specific characteristics that might differ from those of a standard subject. ISO 9886 describes how physiological parameters must be used to monitor the physiological behaviour of a particular subject and ISO 12894 describes how medical supervision must be organized. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=Aramco HQ/9980755100 Not for Resale, 04/11/2007 04:37:11 MDTNo reproduction or networking permitted without license from IHS -,-,- Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=Aramco HQ/9980755100 Not for Resale, 04/11/2007 04:37:11 MDTNo reproduction or networking permitted without license from IHS -,-,- INTERNATIONAL STANDARD ISO 7933:2004(E) © ISO 2004 All rights reserved 1 Ergonomics of the thermal environment Analytical determination and interpretation of heat stress using calculation of the predicted heat strain 1 Scope This International Standard specifies a method for the analytical evaluation and interpretation of the thermal stress experienced by a subject in a hot environment. It describes a method for predicting the sweat rate and the internal core temperature that the human body will develop in response to the working conditions. The various terms used in this prediction model, and in particular in the heat balance, show the influence of the different physical parameters of the environment on the thermal stress experienced by the subject. In this way, this International Standard makes it possible to determine which parameter or group of parameters should be modified, and to what extent, in order to reduce the risk of physiological strains. The main objectives of this International Standard are the following: a) the evaluation of the thermal stress in conditions likely to lead to excessive core temperature increase or water loss for the standard subject; b) the determination of exposure times with which the physiological strain is acceptable (no physical damage is to be expected). In the context of this prediction mode, these exposure times are called “maximum allowable exposure times”. This International Standard does not predict the physiological response of individual subjects, but only considers standard subjects in good health and fit for the work they perform. It is therefore intended to be used by ergonomists, industrial hygienists, etc., to evaluate working conditions. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 7726, Ergonomics of the thermal environment Instruments for measuring physical quantities ISO 8996, Ergonomics of the thermal environment Determination of metabolic rate ISO 9886, Ergonomics Evaluation of thermal strain by physiological measurements ISO 9920, Ergonomics of the thermal environment Estimation of the thermal insulation and evaporative resistance of a clothing ensemble Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=Aramco HQ/9980755100 Not for Resale, 04/11/2007 04:37:11 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 7933:2004(E) 2 © ISO 2004 All rights reserved 3 Symbols For the purposes of this document, the symbols and abbreviated terms, designated below as “symbols” with their units, are in accordance with ISO 7726. However, additional symbols are used to for the presentation of the Predicted Heat Strain index. A complete list of symbols is presented in Table 1. Table 1 Symbols and units Symbol Term Unit code = 1 if walking speed entered, 0 otherwise code = 1 if walking direction entered, 0 otherwise fraction of the body mass at the skin temperature dimensionless i skin-core weighting at time ti dimensionless i1 skin-core weighting at time ti1 dimensionless emissivity dimensionless angle between walking direction and wind direction degrees ADu DuBois body surface area square metre Ap fraction of the body surface covered by the reflective clothing dimensionless Ar effective radiating area of a body dimensionless C convective heat flow watts per square metre ce water latent heat of vaporization joules per kilogram Corr,cl correction for the dynamic total dry thermal insulation at or above 0,6 clo dimensionless Corr,Ia correction for the dynamic total dry thermal insulation at 0 clo dimensionless Corr,tot correction for the dynamic clothing insulation as a function of the actual clothing dimensionless Corr,E correction for the dynamic permeability index dimensionless cp specific heat of dry air at constant pressure joules per kilogram of dry air kelvin Cres respiratory convective heat flow watts per square metre csp specific heat of the body watts per square meter per kelvin Dlim maximum allowable exposure time minutes Dlim tre maximum allowable exposure time for heat storage minutes Dlimloss50 maximum allowable exposure time for water loss, mean subject minutes Dlimloss95 maximum allowable exposure time for water loss, 95 % of the working population minutes Dmax maximum water loss grams Dmax50 maximum water loss to protect a mean subject grams Dmax95 maximum water loss to protect 95 % of the working population grams DRINK 1 if workers can drink freely, 0 otherwise dimensionless Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=Aramco HQ/9980755100 Not for Resale, 04/11/2007 04:37:11 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 7933:2004(E) © ISO 2004 All rights reserved 3 Symbol Term Unit dSi body heat storage during the last time increment watts per square metre dSeq body heat storage rate for increase of core temperature associated with the metabolic rate watts per square meter E evaporative heat flow at the skin watts per square metre Emax maximum evaporative heat flow at the skin surface watts per square metre Ep predicted evaporative heat flow watts per square metre Ereq required evaporative heat flow watts per square metre Eres respiratory evaporative heat flow watts per square metre fcl clothing area factor dimensionless Fcl,R reduction factor for radiation heat exchange due to wearing clothes dimensionless Fr emissivity of the reflective clothing dimensionless Hb body height meters hcdyn dynamic convective heat transfer coefficient watts per square metre kelvin hr radiative heat transfer coefficient watts per square metre kelvin Ia st static boundary layer thermal insulation square meters kelvin per watt Icl st static clothing insulation square meters kelvin per watt Icl clothing insulation clo Itot st total static clothing insulation square meters kelvin per watt Ia dyn dynamic boundary layer thermal insulation square meters kelvin per watt Icl dyn dynamic clothing insulation square meters kelvin per watt Itot dyn total dynamic clothing insulation square meters kelvin per watt imst static moisture permeability index dimensionless imdyn dynamic moisture permeability index dimensionless incr time increment from time ti1 to time ti minutes kSw fraction k of predicted sweat rate dimensionless K conductive heat flow watts per square metre M metabolic rate watts per square meter pa water vapour partial pressure kilopascals psk,s saturated water vapour pressure at skin temperature kilopascals R radiative heat flow watts per square metre rreq required evaporative efficiency of sweating dimensionless Rtdyn dynamic total evaporative resistance of clothing and boundary air layer square metres kilopascals per watt S body heat storage rate watt