6 Closed Deck Risk Estimate Calculation
The probability of heat stress or mortality for particular lines of stock being transported on a particular ship depends on:
The type, breed, coat, condition, acclimatization and weight of livestock The particular ventilation rate PAT deck of the ship they are being transported on
The time of year of the voyage The voyage route, destination port and duration of transit or stay in critical zones.
The statistical treatment of the above data has been as follows: The wet bulb temperature data are fitted to a Normal distribution Section 2.3.
The survival rate of livestock will be assumed to conform to a beta distribution Sections 3.2 and 3.3.
The calculation procedure by which the above information is used to estimate risk is detailed in Section 6.2.
6.1 Deck Wet Bulb Temperature Rise
The environmental parameters relevant to the animals are not the ambient conditions but those in the pens. Following previous work SBMR.002, the average rise in wet bulb
temperature between ambient and exhaust flows is given by: UTwb = 3.6 x C x M x h
ρ x PAT
where: UTwb is the wet bulb temperature increase C
C is the ‘constant’ of proportionality relating UTwb to the internal energy rise. We have taken this as 0.23
CkJkg M is the liveweight in the particular ventilation zone kgm
2
M = beast weight ÷
area per head 275kgm
2
for cattle, 180kgm
2
for large sheep, etc.
h is the ‘per mass’ rate of metabolic heat. This is variable however here we will take 2Wkg for Bos indicus cattle, 2.4Wkg for Bos taurus cattle and 3.2Wkg for
sheep. ρ
is the density of air 1.2kgm
3
PAT, the pen air turnover in mhr, is the ratio of the fresh air flowrate Q in m
3
hr to the pen area A in m
2
The factor 3.6 at the front corrects units from W to kW and hours to seconds. For deck areas with very low ventilation rates, there may be little jetting and slow mixing
around the deck. In such cases, there may be differences in wet bulb temperature around the deck. Where air supply is strong, the assumption that the deck air is evenly mixed is a
reasonable one, with air inlet jetting causing fairly rapid swirl and mixing around the deck. To the extent that there are small differences in wet bulb temperature between apparently
identical pens on one deck, the resulting spread in primal response will be indistinguishable experimentally from the physiological variability of the animals. That is; the variability in
below-deck conditions will effectively widen the limits of the beta distribution assumed for the animals. Since those distributions are, to some degree, uncertain, a correction to them may
be even less certain. More importantly, the beta distributions have been based on estimated 50 percentile data and estimates of wet bulb temperature causing 0.5 to 2 percent mortality
rates on real ships. Because the data are sourced from the ships, they inherently include the
Project: LIVE.116 – Development of a Heat Stress Risk Management Model Revision F
Maunsell Australia Pty Ltd Page 48 of 129
Final Report December 2003
effects of the deck non-uniformity on those ships. The difficult task of deck non-uniformity correction is thus avoided for the risk assessment.
Because the deck wet bulb temperature rise is a function of both PAT and the stocking rate, the effective deck wet bulb probability is calculated for each stocking entry in the software. A
stocking entry is one line of animal on a particular deck.
6.2 Statistical Combination of Weather and Animal
