vary to some degree throughout any cargo. Therefore, we believe there is a case for a campaign of awareness of this problem, and an investigation of the sampling errors that are present in practice. How bad is it for different cargoes? Which cargo flows are the one ones at high risk due to heterogeneity and sampling errors, and which are not? Much work has been done to get accurate FMP tests. Much work has been done to try to understand liquefaction better – the recent work of the Global Bauxite Working Group, convened following the loss of the Bulk Jupiter, is an exemplary piece of science and very illuminating regarding how bauxite can behave; it also makes interesting recommendations on predicting the danger for any given cargo, but the measurements still rely on samples. All the evidence we have, is that the inaccuracy in sampling is sometimes (maybe frequently) so big as to defeat the best of current protocols. The industry needs to start looking at this sampling error problem just as seriously as we have all been looking at FMP measurement.
At the very least, the matter of stockpile heterogeneity and its effect on the meaning of FMP and MC measurements due to sampling errors, needs to be raised and awareness widened.
AN IMPROVED TEST FOR USE SHIP-BOARD The current IMO code for group A cargoes stresses the need for vigilance on the part of the master, crew and cargo superintendent to look out for signs that the cargo in dangerous, even if the certificated MC and TML are in order. This is especially stressed in the case of nickel ore. The protocol strongly suggests the use of the “can test” as well looking for as signs of “splashing”.
For certain cargoes and loading operations we feel this is especially important, again for example raw ores which have a high likelihood of a significant sampling error, at ports where there is frequent rain on the cargo during loading, and especially where the loading takes place slowly using double-handling via barges so has great exposure to weather. The value of the FMP and MC tests and the safety given by certification will always be doubtful in certain cases. Also, masters know full well that a cargo certificate could be falsified.
These are the cases when a test that could be performed by the master during loading, would act as a “last line of defence” against loading a dangerous cargo. The Intercargo 2012 note “Nickel Ore – Stop, Think, Verify” is very explicit in stressing that that certification alone is NOT enough, and vigilance during loading is essential. However, the problem is that the “can test” is really the only quantification option a master has to do this, but as the note points out, the can test cannot show that a cargo is safe – it only shows when the margin of safety in a sample has been eroded completely so that the MC is above the FMP.
In other words, a failed
can test says “definitely dangerous” whereas a passed can test says “might be safe but not definite”. The note recommends the use of the can test but rightly suggests that any failed can test should lead to rejection of the whole cargo; in practice we have known masters to use the “can test” as a “go/no-go tool for selecting portions of the cargo to accept and reject, against the advice of the note. A more reliable test would allow this to be done on a sound basis.
At The Wolfson Centre we have been working on this and come up with an idea for a test that could
replace the “can test” at low cost, is easy to use by a non-specialist and shows not just when the MC exceeds the FMP, but when a predetermined margin between MC and FMP is present – ie when the sample is actually “safe”. Essentially, instead of measuring the moisture in the sample and comparing against the moisture level at which another sample becomes saturated, the test uses Archimedes principle to measure the air voids within the sample when densified.
If, when a
material is compacted, there is still a definite amount of air present between the particles, then it cannot become saturated so cannot liquefy. Determining a definite amount of such air voidage gives a definite indication of safety margin on that very sample, so it eliminates the double sampling error arising from the MC and FMP being determined on different samples.
We believe that such a test could also be used shore-side on samples from a stockpile, to evaluate the safety of a cargo prior to loading. It would be cheaper and faster to use than the current oven drying test, requiring less specialised equipment, and shows whether there is an acceptable margin between MC and FMP on each individual sample, eliminating the double sampling error arising from MC and FMP being measured on different samples as at present. Multiple samples would still be required – but the test would be more reliable, and the sampling error less.
SUPPORT AND INTEREST Taking either of these matters forwards would require some support, at least to know that there is interest in them in the first instance. Contact should be made with the author of this article in the first instance, or via Ian Adams at the Dry Bulk Terminals Group.
The Report • September 2017 • Issue 81 | 71
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