Development of a heat stress risk management model

Summary

This final report documents the data analysis, mathematical modeling and software development of ‘HS’, a program to estimate the risk of mortality due to heat stress in livestock decks on voyages from Australia to the Middle East. The report now includes the risk management model for open decks which is also fully implemented in the software. The software has been expanded and revised following industry workshops and is now released as “HS Version 2.1”.

The risk assessment method takes account of weather at destination and en route, animal acclimatisation, coat and condition and the ventilation characteristics of the ships.

Very little solid information is available to assist the assessment of animal mortality limits. The available data have been used to extrapolate to other animals using scaling based on dimensional analysis and knowledge of heat transfer behaviour. The weather data are also uncertain to some extent and we have decreased the observing ships’ wet bulb data probability distributions by 1oC to allow for known data deficiencies which cannot be fully corrected. With adjustments so made, it is felt that the risk predictions for voyages are neither overly conservative nor overly optimistic. This is confirmed by a new validation based on analysis of voyage 20 of the Al Shuwaikh. Certainly, high risk voyages will be identified and prevented in the future. There will always be some grey areas in estimating lower level risks around the level of the target risk limit.

Further animal house work and voyage weather and animal observations will allow the input data to be improved with time, possibly resulting in adjustments to the model. It is suggested that the model, the software and the outcomes be reviewed annually following the northern summer.

There is little recorded information on the temporal variation of wind in discharge ports. For this reason, the proposed method for control of heat stress risk on open decks is different to that for closed decks. For open decks we recommend that:

Open decks on new ships should be ventilated and assessed as for closed decks
Existing ships with mechanical PAT on open decks of less than 150m/hr should undertake engineering investigations to identify all reasonably practical measures for improving PAT.
Open decks not assessed as for closed decks shall be operated according to protocols designed to minimize still air risks (operational guidelines are given).