1、| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | BRITISH STANDARD BS 7915:1998 ICS 13.180 N
2、O COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW Ergonomics of the thermal environment Guide to design and evaluation of working practices for cold indoor environmentsThis British Standard, having been prepared under the direction of the Health and Environment Sector Committee,
3、was published under the authority of the Standards Committee and comes into effect on 15 November 1998 BSI 1998 The following BSI references relate to the work on this standard: Committee reference PH/9/1 Draft for comment 96/500807 DC ISBN 0 580 29598 2 BS 7915:1998 Amendments issued since publicat
4、ion Amd. No. Date Text affected Committees responsible for this British Standard The preparation of this British Standard was entrusted by Technical Committee PH/9, Applied ergonomics, to Subcommittee PH/9/1, Thermal environments, upon which the following bodies were represented: British Occupationa
5、l Hygiene Society British Textile Technology Group Cold Storage and Distribution Federation Consumer Policy Committee of BSI Health and Safety Executive Home Office Institute of Occupational Medicine Institution of Fire Engineers Ministry of Defence Transport and General Workers Union Coopted member
6、sBS 7915:1998 BSI 1998 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Normative references 1 3 Terms, definitions and symbols 1 4 Human responses to cold 2 5 The assessment of cold environments 2 6 Risks from cold environments 4 7 Minimizing the effects of the cold
7、 environment 5 Annex A (informative) Examples of metabolic rate of work in cold environments 8 Annex B (informative) Examples of clothing worn and corresponding insulating values 8 Annex C (informative) Examples of acceptable clothing ensembles for typical working environments 9 Bibliography 13 Tabl
8、e 1 Wind chill index: corresponding chilling temperatures and likely effects 3 Table A.1 Examples of metabolic rate of work in cold environments 8 Table B.1 Examples of corresponding insulating values for clothing worn 8 Table C.1 Equipment used to measure environmental conditions 10ii BSI 1998 BS 7
9、915:1998 Foreword The British Standard has been prepared by Subcommittee PH/9/1. Annexes A, B and C are informative. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a
10、British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 13 and a back cover. BSI 1998 1 BS 7915:1998 1 Scope This British Standard gives guidance on ways in which cold stress
11、 or discomfort in cold indoor environments can be evaluated and cold strain reduced. It describes the human responses (physiological and behavioural) to the cold, together with the influence of different working practices on these. The risks from cold environments are also described. This British St
12、andard applies to those indoor environments which are either cold by design or by virtue of a designed process. It does not apply to outdoor work or those environments which, although largely enclosed, are cold by virtue of exposure to the external climate (e.g. unenclosed loading bays, tyre fitting
13、 bays, farm out-buildings). For the purposes of this British Standard, cold environments are taken to be those with an air temperature of 128C or less. NOTE The lower limit of application of this British Standard has not been rigorously defined. In survey work, temperatures down to2408C were encount
14、ered, with one application at a lower temperature. At temperatures below2408C, hazards not considered in this document, for example to the respiratory tract, are known to exist. 2 Normative references The following normative documents contain provisions which, through reference in this text, constit
15、ute provisions of this British Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. For undated references, the latest edition of the publication referred to applies. BS EN 511, Specification for protective gloves against cold. BS EN 2772
16、6, Thermal environments Instruments and methods for measuring physical quantities. BS ISO 9920, Ergonomics of the thermal environment Estimation of the thermal insulation and evaporative resistance of a clothing ensemble. 3 Terms, definitions and symbols For the purposes of this standard, the follow
17、ing terms, definitions and symbols apply. 3.1 Terms and definitions 3.1.1 contact period time during which contact with the surface takes place 3.1.2 thermal inertia product of the density, thermal conductivity and specific thermal capacity of the surface 3.1.3 material properties chemical/physical
18、composition of the material and the characteristics (rough, smooth) and shape of the surface 3.1.4 air temperature temperature of the air surrounding the human body 3.1.5 absolute humidity mass of water vapour contained in a given mass of air 3.1.6 mean radiant temperature uniform temperature of an
19、imaginary enclosure in which the radiant heat transfer from the human body is equal to the radiant heat transfer in the workplace 3.1.7 metabolic rate rate of transformation of chemical energy into heat and mechanical work by aerobic and anaerobic metabolic activities within an organism 3.1.8 cold s
20、tress index mechanism by which appropriate factors are integrated into a single number, which indicates the likely resulting cold strain 3.2 Symbols DLE neut duration limited exposure for neutral criteria DLE min duration limited exposure for minimal criteria IREQ neut neutral required clothing insu
21、lation IREQ min minimal required clothing insulation t a air temperature t ch chilling temperature t r mean radiant temperature t s temperature of surrounding surfaces WCI wind chill index NOTE The majority of the symbols in this British Standard guide have been taken from ISO/TR 11079.2 BSI 1998 BS
22、 7915:1998 4 Human responses to cold 4.1 Physiological responses The human body is not generally well-equipped physiologically to cope with cold environments. The two principal responses are: a) to increase heat production, partly by muscular activity such as shivering and partly by secreting hormon
23、es to increase the basal metabolic rate of the body; b) to reduce heat loss by constricting the blood vessels of the skin (cutaneous vasoconstriction). In response to these changes the oxygen uptake by the body will increase and cardiac output rise. If cold exposure continues, or if it is sufficient
24、ly severe, then cooling of the hands, feet, ears and face may result in their blood vessels dilating intermittently (cold vasodilation). 4.2 Behavioural responses The initial, tangible impact is one of subjective discomfort, either of the whole body or localized to specific areas of the body. Even w
25、here reasonable levels of insulation are provided, exposed peripheral sites such as hands and feet are particularly susceptible to local discomfort. Cold may distract workers and alter behaviour, which may have consequences for safety and productivity. 5 The assessment of cold environments 5.1 Gener
26、al Cold strain arises from an imbalance in the heat exchange between the body and its surrounding environment. In assessing the likelihood of such strain occurring it is necessary to consider: a) the external (thermal environment) parameters which influence heat exchange; b) the internal (metabolic)
27、 heat production, which is related to physical activity; c) the boundary between a) and b), principally influenced by clothing insulation. The individual elements of a) to c) are described in 5.2 to 5.4. 5.2 Environment 5.2.1 Introduction The four environmental parameters that are physiologically re
28、levant are: a) air temperature (see 5.2.2); b) humidity (see 5.2.3); c) air velocity (see 5.2.4); d) radiant temperature (see 5.2.5). The instruments and methods for their measurement are described in BS EN 27726. The principle is to quantify the environment where people are located. 5.2.2 Air tempe
29、rature In cold conditions, the air temperature is one of the most influential factors in determining the degree of cold stress experienced. 5.2.3 Humidity Measures such as the relative humidity or the saturation level define the amount of water vapour in the air in relation to the maximum amount tha
30、t it can contain at a given temperature. In cold conditions the water vapour capacity of the air is low and humidity therefore has a minimal effect on physiological heat balance although it may affect thermal comfort. 5.2.4 Air velocity The air velocity is a quantity defined by its magnitude and dir
31、ection. In practice, it is the magnitude (air speed) which is often used. In cold conditions the air velocity may have a marked effect on heat exchange, causing wind-chill and general heat loss by removing the warmed boundary layer from the surface of the body. In addition, fluctuations in air veloc
32、ity or turbulent flow promote subjective discomfort (draughts). 5.2.5 Radiant temperature asymmetry Where the radiant temperature is likely to be highly asymmetric, such as proximity to surfaces at a substantially lower surface temperature than the surrounding air, or where heat radiating devices ar
33、e used, it may be appropriate to measure this asymmetry. 5.3 Activity level The level of activity will determine metabolic rate and therefore metabolic heat production. Methods for the determination of metabolic heat production are described in BS EN 28996 which provides for three different levels o
34、f determination of increasing accuracy. NOTE Annex A provides a table of examples of values based on the simplest of these approaches described in BS EN 28996, with examples related to work in cold conditions. 5.4 Clothing insulation Methods for the estimation of the thermal characteristics (resista
35、nce to dry heat loss and evaporative heat loss) for a clothing ensemble are given in BS ISO 9920. The insulating value of an item of clothing or a clothing ensemble is conveniently cited using the clo unit (1 clo = 0.155 m 2 8CW -1 ). NOTE Annex B provides examples of insulation values of clothing u
36、sed in cold conditions. An estimation of the required level of insulation can be determined from ISO/TR 11079, which describes the IREQ index (see 5.5.2). This index utilizes the parameters given in 5.2.1 to estimate the level of insulation required for a given set of environmental and metabolic con
37、ditions to maintain the body in a state of thermal equilibrium at acceptable levels of body and skin temperature. BSI 1998 3 BS 7915:1998 Where the insulation provided is less than that required it also allows the calculation of an acceptable exposure period known as the duration limited exposure (D
38、LE). 5.5 Cold stress indices 5.5.1 Insulation required (IREQ) As well as being used to determine particular clothing ensembles required for particular environments, the IREQ value can be used as an index in the following forms. a) IREQ neut is the thermal insulation required to provide conditions of
39、 thermal neutrality. This represents no or low physiological strain. b) IREQ min is the minimum thermal insulation required to maintain body thermal equilibrium at a subnormal level of mean body temperature. This represents the highest level of physiological strain to which humans should be exposed
40、when performing occupational work. Details are available in ISO/TR 11079 which includes a computer program listing. 5.5.2 Wind chill index ISO/TR 11079 also describes the calculation of the wind chill index (WCI), which indicates the rate of heat loss from unprotected skin. It is principally intende
41、d for use in outdoor conditions, and the air velocity used as a baseline (calm) reference (1.8 ms 21 ) is much higher than would normally be recommended for indoor working. It may, however, be of some value in specific circumstances such as blast freezers. The wind chill index, in watts per square m
42、etre (W/m 2 ) may be calculated by the following equation: 1.163 (10 + 10.52 v) (332 t a ) v where v is the air velocity, in metres per second (ms -1 ); t a is the air temperature, in degrees Celsius (C). A related index is the chilling temperature, t ch . This is the air temperature that would give
43、 the equivalent effect as the actual conditions, (the same WCI value), but in calm conditions (defined as v =1 .8m s 21 ). The chilling temperature, t ch , in degrees Celsius (C), is given by the following equation: t ch =3 32 WCI 25.5 where WCI is the wind chill index in watts per square metre (W/m
44、 2 ). A scale showing the effects is given in Table 1. Table 1 Wind chill index: corresponding chilling temperature and likely effects WCI t ch Effect W/m 2 8C 1 200 214 Very cold 1 400 222 Bitterly cold 1 600 230 Exposed flesh freezes within 1 h 1 800 238 2 000 245 Exposed flesh freezes within 1 mi
45、n 2 200 253 2 400 261 Exposed flesh freezes within 30 s 2 600 269 5.6 Subjective assessment The subjective assessment of thermal comfort or thermal sensation is the subject of two standards. BS EN ISO 7730 addresses the issue of comfort in moderate thermal environments. However, its application is l
46、imited to environments with air temperatures in excess of 108C and it is therefore of limited utility in the environments covered by this standard. BS ISO 10551 provides guidance on the construction and use of judgement scales for use in providing reliable and comparative data on the subjective aspe
47、cts of thermal comfort or discomfort. 5.7 Contact with cold surfaces At present, no standard exists which provides guidance on the effects of contact with cold surfaces. However, many of the principles involved in terms of factors affecting the likelihood of skin damage are defined and described in
48、BS EN 563 which gives guidance in relation to contact with hot surfaces. The relevant factors are: a) surface temperature; b) contact period (see 3.1.1); c) thermal inertia (of the touched material) (see 3.1.2); d) material properties of the surface (of the touched material) (see 3.1.3). Lower surfa
49、ce temperatures, longer contact periods, low thermal inertia, and smoother surfaces will all tend to increase heat transfer (from the skin to the contacted material) and therefore increase the risk of cold damage. The guidance given in BS EN 563 in relation to the characteristics of different types of material will also provide qualitative guidance for the impact of cold contact. As a general guide, contact with bare metal at temperatures below278C can rapidly cause cold injury to bare skin.4 BSI 1998 BS 7915:1998 5.8 Conducting an assessment 5.8.1 Introduct
