The user centred design, development and evaluation of a practical heat stress risk assessment method
thesisposted on 22.02.2011, 09:35 authored by Damian Bethea
A five stage systems life-cycle was adopted. Stage 1 involved a literature review and hierarchal tasks analysis of existing European and British heat stress standards. The literature review developed the rationale for the study by providing a knowledge framework on human thermal environments and human thermoregulation. This was supplement by a review of occupational heat stress. Stage 2 consisted of a series of ten experiments conducted at the Human Thermal Environments Laboratory at Loughborough University to compare the validity of ISO 7933 Required Sweat Rate (SWrcq) and Predicted Heat Strain (PHS) index predictions with observed physiological data. Comparisons were made between the predicted and observed sweat rates and the time it took core temperature to reach 38°C (Duration Limit Exposures). The results showed that neither the SWieq nor the modified SWreq model were valid predictors of Duration Limit Exposures (DLE) and predicted sweat rate for people wearing protective clothing in warm humid environments. The PHS DLE predictions were more representative of the ISO predictions than observed DLEs in all but one experiment. Although the PHS model predictions of sweat rate were an improvement on the ISO predictions, the model also significantly underestimated the observed sweat rates. Stage 3 provided the Exploratory Stage for the identification of appropriate ergonomic methods to collect the data necessary for the design, development and evaluation of a practical heat stress method for use in British Industry. A heuristic evaluation of the usability of ISO 7933 SWTreq was conducted. This found that the standard is unnecessarily scientific and may not encourage users to use it. The format and the information provided do not satisfy ergonomic guidelines of usability. The need for a more practical heat stress assessment methodology was identified. Stakeholder engagement through a practical field study of heat stress in a paper mill, together with informal interviews and discussion groups with potential users provided a framework for formulating the design, development of a prototype method. Stage 4 was the Design Stage. Expert discussion groups and the results of a postal questionnaire combined with the findings of Stage 3 provided for the user requirements and the functional specification of such a methodology to be established. This showed that a simple approach, together with additional information (e.g. expert systems, job aides etc) was required. A process flow diagram of heat stress risk assessment was developed as was a prototype Observation Checklist. In Stage 5 the Prototype Observation Checklist was evaluated in a comparative study with the Malchaire method (developed as part of the BIOMED II project). Although the Malchaire method was found to easier to use it did not meet the user's requirements. The outcome of Stage 5 was the development of a two part practical heat stress method. Both are based on simple checklists. Part A is concerned with identifying people who may be at added risk from working in the heat. Part B provides a checklist based on the six basic parameters of the human thermal environment; air and radiant temperature, humidity, air movement, clothing and metabolic rate. A score sheet is provided to allow users to identify factors of greatest risk. This forms part of a holistic approach to the Management, Assessment and Control (MA&C) of heat stress. Job aides such competency checklists, specimen record sheets and information for managers are also provided.
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