7 Open Deck Risk Management
7.1 Overall Approach
Section 5 indicates the degree to which cross wind controls conditions in open decks. An assessment of risk on open decks also requires a knowledge of the wind behaviour in ports
of discharge. There are two approaches to this. The first is to assess the fraction of time for which the wind is below some critical level. This approach however, ignores the ability of the
ship’s master to avoid the obvious still conditions. The real statistic of interest is the probability that the cross wind drops below the ‘critical’ level while the vessel is in port,
catching the master by surprise. Unfortunately, while we have identified the statistic of interest, the available data are patchy and give no such temporal information. There are
insufficient data to realistically identify true diurnal trends. The countries contacted for more detailed port wind data were not able to provide it. The ship wind data available are largely
recorded by humans and exhibit known biases. There is a tendency for wind speeds to be recorded in multiples of 5 knots. Some numbers e.g. 11 are not favoured by humans.
There is also a slight bias against odd numbers except 5. In higher wind speeds, there is a tendency to bias the observation towards the higher wind gusts rather than the true mean
wind speed. This characteristic becomes less evident in wind speeds below 15 knots. A targeted monitoring programme in the discharge ports would help to fill the information
void, however initial data would only be applicable one year after commencement, with statistics becoming more solid over several years.
As the wind data limitations preclude a numerical risk estimation for open decks as done for the closed decks, we cannot foresee an ‘acceptable risk’ benchmark for open decks. Across
many industries, the approach in such instances of ill-defined probability is to take measures to make the risk ‘as low as reasonably practical’. This approach, often labelled with the
acronym ‘ALARP’, obviously has less statistically predictable outcomes and the benchmark is set not by a risk level but by consideration of what risk reduction measures are ‘reasonably
practical’ and whether those measures have been taken in this respect, the open deck risk approach becomes more like that applied to the risk of salmonellosis.
It is our view that, for ships built after the date of Revision D of this report, it is reasonably practical to mechanically ventilate open decks to give effective pen air turnovers in still air
that would meet risk requirements if assessed as a closed deck. That is; we recommend that risk for open decks on newly built vessels be assessed as for closed decks. While this
may add capital cost it is not certain, it will reduce the risk of heat stress and, at the same time, free the vessel from operational restrictions on docking when ‘still’ air is likely.
The avoidance of risk and achievement of greater operational flexibility are in themselves good business reasons for ‘full’ ventilation of open decks and may, on a cost benefit
analysis, justify any extra capital and operating costs involved. For open decks on existing vessels, which cannot already meet closed deck risk criteria, the
‘reasonably practical’ benchmark will obviously be different. We consider that it is reasonably practical for most of the existing fleet to ‘re-furbish’ existing ventilation systems to
increase flowrate. We understand that there are many ships which have still not taken such simple measures as replacing tight ‘mushroom cap’ inlets with either bell mouth inlets or low-
loss covered inlets. Other opportunities to economically improve open deck air supply on a ship by ship basis
should be identified by a professional engineering review of each ship involving both measurement and calculation. In order to avoid a conflict of interest in making such a firm
recommendation in this report, Maunsell will, on request, nominate others who are capable of undertaking the work.
Project: LIVE.116 – Development of a Heat Stress Risk Management Model Revision F
Maunsell Australia Pty Ltd Page 51 of 129
Final Report December 2003
Once all reasonably practical measures have been taken with the ship’s equipment to give generous supply air flows, if the open deck risk is still not acceptable by closed deck
assessments, the ‘reasonably practical’ benchmark is different again. Having exhausted equipment options, we look to the reasonably practical operating
measures. There are opportunities for operating ships to avoid still air and to use crosswind beneficially. The practical avoidance of still air requires knowledge of the port weather
patterns. We give below general descriptions of the discharge port wind patterns, followed by ‘reasonably practical’ guidelines for when not to dock. The generality of the information
on which these criteria are based and their simplistic nature mean that they are likely to be inaccurate in some circumstances. The criteria are intended to be separable from this
report, to be updated and maintained by the industry as further data come to hand. In summary, we propose that the risk management of open decks be addressed in three
ways: i
Build new ships with ‘full’ ventilation of open decks and assess risk on those vessels as for closed decks. Over many years, with fleet renewal, this will make other
approaches redundant. ii
Improve the ventilation of existing open decks as far as is reasonably practical. iii
Require that open decks not meeting closed deck criteria be operated to a set of guidelines which minimise the risk due to low crosswind.
7.2 Discharge Port Wind Behaviour
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