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Thomas E. Bernard

Heat Stress

Thomas E. Bernard

Current Site Status -- Under construction and should be available by 1 December 2021

Last Update: 24 September 2014. The most recent additions are an update to a suite of Excel® User Defined Functions for psychrometric and weather data (see Basic Tools). The WBGT detailed analysis (WBGTv50) was also added and corrected a problem with grouped sheets.

The following materials are intended to support and expand the application of ACGIH® TLV® for heat stress and strain. The worksheets are intended for training and are not offical interpretations of the TLV®

Typically, an Analysis Package is written in Excel® and has macros that must be enabled to fully function. The worksheets are protected to keep users in the data entry areas; some can be unprotected without a password. There will be a movement of the Excel workbooks to the most recent file formats (.xlsx and .xlsm). Because some systems block files with macros (i.e., .xlsm files) and the new extensions, these files are zipped and must be uncompressed before using. Some of the workbooks are protected to conceal propriatary information; contact me to request an unprotected copy.

The materials are copyrighted by me and are intended for personal and professional use with appropriate recognition. It would be nice to hear from you by email about materials you find helpful.

The TLV® for heat stress and strain was described in a webinar offered by the ACGIH® in April 2006 and June 2013. Please see the ACGIH® website for information on obtaining a copy of the webinar.

TLV Flow Chart - ACGIH® TLV® for Heat Stress and Strain (2006)

  • Psychrometric Relationships

    Can be used to determine other psychrometric properties from any two and can be used to estimate natural wet bulb temperature. This work provides a method to estimate WBGT from ambient data.

    Analysis Package
    v 1.0 (1/22/2005)

    Psychrometric Macro Functions for Excel

    These Excel functions are designed to compute water vapor pressure, relative humidity, psychrometric wet bulb temperature, natural wet bulb temperature and US NWS Heat Index from environmental data. More about each function is provided in the file. The code is available in a text file format for use in Excel. Once available in Excel, the function is used like an Excel built-in function, which returns a value based on the referenced input cells.

    Package in text file
    v 2.0 (8/31/2014)

    Estimation of Metabolic Rate

    Methods include ISO and Qualitative Descriptors plus equations for selected activities.

    The newest versions (v3 for Analysis Package and v2 for Manual Method) have an expanded set of equations including an adaptation of Garg's equations to estimate metabolic rate.

    Analysis Package
    v 3.1 (7/28/2005)

    Manual Method
    v 2.0 (8/6/2006)

    Estimation of WBGT from Dry Bulb Temperature and Dew Point or Relative Humidity

    Tables are provided in °C-WBGT and °F-WBGT and can be copied into other documents.

    The tables use air temperature and a measure of humidity (either dew point or relative humidity). Version 2.1 corrects the table label for dew point temperature.

    v2.1 (7/23/2013)

  • Qualitative Exposure Assessment

    Two methods are provided. One has been published and the other reflects some of my thoughts (unpublished).

    Qual Exp Ass't
    v 1.0 (8/19/2001)
    WBGT Screening for Heat Stress Manual Screen
    v 2.2 (4/14/2006)

  • WBGT

    The basic time-weighted average method for exposure assessment. Analysis Package has routines to estimate WBGT.

    Analysis Package
    v 5.0 (5/17/2013)

    Manual Method
    v 3.2 (4/14/2006)

    Rational Heat Stress Analysis Package

    The Excel workbook is built on the Predicted Heat Strain model described in ISO 7933 (2004) and papers published by Prof. J. Malchaire. An additional feature is the inclusion of clothing adjustments based on ISO9920 (2007). Imperial (Traditional US) units are not supported.

    Analysis Package
    v 2.0 (11/29/2013)
    PrevHeat: Qualitative PHS Exposure Assessment

    PrevHeat is an Excel-based qualitative exposure assessment method based on the ISO 7933 (2004) Predicted Heat Strain. Click on Prevheat under the desired language and follow the directions carefully.

    Link to Prof. Jacques Malchaire
    Recovery Allowances

    This is a major revison in terms of presentation of the allowances. The user specifies up to five metabolic rates, clothing adjsutment factor and the WBGT of the recovery area. Both tables and graphs are provided for recovery in the same area and recovery in a different area with work clothes. WBGT is presented in °C-WBGT and °F-WBGT.

    Version 4 had a programming error that did not update the metabolic rates from the values in the distribution copy. This has been corrected in Version 5 along with some minor changes.

    If WBGT instrumentation is not available, see tables in Basic Tools for estimating the WBGT.

    Analysis Package
    v 5.0 (9/12/2013)
    Short-Term Exposure Limit

    An empirical relationship to recommend time limits for high heat stress exposures based on WBGT and allowing for metabolic rate and clothing. Note: There is some indication that the exposure times are not as protective as the data would suggest.

    See Bernard, T. E., C. D. Ashley. Short-term heat stress exposure limits based on wet bulb globe temperature adjusted for clothing and metabolic rate. Journal of Occupational and Environmental Hygiene 6:632-638, 2009

    Analysis Package
    v 1.0 (3/13/2009)
    Estimation of Exposure Time with Ice Cooling Personal Protection

    An estimate of the amount of time a person can stay in a hot environment while wearing a personal cooling system with an ice heat sink.

    Manual Method
    v 1.0 (2/5/2007)