TR 46-02 - Sanas

TR 46-02CONTENTS:1. Background ...................................................................................................................... 32. Purpose and Scope .......................................................................................................... 33. References ....................................................................................................................... 34. Definitions and Abbreviations ........................................................................................... 35. Environmental Requirements ............................................................................................ 46. General Requirements ...................................................................................................... 47. Technical Requirements ................................................................................................... 4APPENDIX 1: ISO 7243 : 1989 Accuracy Requirements ...................................................... 5APPENDIX 2: ISO 7243 : 1989 WBGT Indices ...................................................................... 5ADDENDUM 1: Amendment Record ....................................................................................... 6©SANAS Page 2 of 6

TR 46-021. BackgroundThe generally accepted method for measuring heat stress risk is the use of the WBGT index. TheWBGT Monitor is an instrument designed specifically to take into account the various environmentalfactors that a worker may be exposed to, these include the ambient temperature, relative humidity, airflow and radiant heat. These readings are combined using an algorithm developed to correlate theexpected human physiological response under different combinations of individual sensor readings, toproduce the ‘WBGT index’.2. Purpose and ScopeThe purpose of this document is to define the requirements for laboratories performing the calibration ofheat stress monitors.3. References[1] OHS Act, 1993 Environmental Regulations for Workplaces, 1987Government Notice R:2281Section 2 – Thermal Requirements[2] SABS ISO/IEC 17025 General requirements for the competence of testing andcalibration laboratories[3] ISO 7243:1989 Hot environments – Estimation of the heat stress on workingman, based on the WBGT-index (wet bulb globe temperature).4. Definitions and Abbreviations4.1 DefinitionsGlobe temperatureThe globe temperature is the temperature indicated by a temperature sensor placed in thecentre of a matt black globe of specific dimensions.[3]Natural wet bulb temperatureThe natural wet bulb temperature is the value indicated by a temperature sensor covered with awetted wick which is ventilated naturally, i.e. placed in the environment under considerationwithout forced ventilation. [3]WBGT Index‘WBGT index’ means a number which characterises the thermal conditions in the environmentto which that number applies; it is calculated by adding seven tenths of the reading in degreesCelsius obtained with a naturally ventilated wet bulb thermometer to one fifth of the rerading indegrees Celsius obtained with the globe thermometer and adding that sum to one tenth of thereading in degrees Celsius obtained by the dry-bulb thermometer; the index may also beobtained using a direct-reading instrument which has been designed, built and calibrated for thatparticular purpose; [1]4.2 AbbreviationsUoMWBGTUncertainty of MeasurementWet bulb globe temperature©SANAS Page 3 of 6

TR 46-02APPENDIX 1: ISO 7243 : 1989 Accuracy RequirementsMeasuring Range Accuracy of MeasurementWet Bulb Sensor 5 to 40 ºC ± 0,5 ºCGlobe Temperature Sensor 20 to 50 ºC ± 0,5 ºC50 to 120 ºC ± 1,0 ºCAir Temperature 10 to 60 ºC ± 1,0 ºCAPPENDIX 2: ISO 7243 : 1989 WBGT Indices• Inside buildings and outside buildings without solar load:WBGT = 0,7 t nw + 0,3 t g• Outside buildings with solar load:WBGT = 0,7 t nw + 0,2 t g + 0,1t aWhere:Natural wet bulb temperature (t nw )Globe temperature (t g )Air temperature (t a )©SANAS Page 5 of 6

TR 46-02ADDENDUM 1: AMENDMENT RECORDProposed By: Section ChangeFM / STC 4 Definition of WBGT Index changed to DoL Government Notice R: 2281definitionFM / STC 7.6 Disclaimer added.©SANAS Page 6 of 6