Weight of Passengers

Both the International Standardisation Organisation and the International Maritime Organisation curently require the use of 75kg as the standard weight of a person for load and stability calculations, including: ISO 14946:2001 Small craft -- Maximum load capacity ISO 12217-1:2002 Small craft -- Stability and buoyancy assessment and categorization -- Part 1: Non-sailing boats of hull length greater than or equal to 6 m.

However the investigation into the “Breakaway 5” hire boat has clearly highlighted the fact that such a figure may well be rather optimistic. Different types of population may also affect the choice of figue.

You can read the full report of the "Breakaway 5" hire boat by visiting http://www.maib.dft.gov.uk/publications/investigation_reports/2004/breakaway_5.cfm. On page 33 of the report the MAIB quote some statistics obtained for them by Qinetiq, giving the probability that a group of ten males, females or mixed will exceed certain weights.

The UK MCA has issued a Marine Information Note on the subject of passenger weight. This MIN is to inform Domestic Passenger Vessel Owners and Operators of the need to have the freeboard and stability of their vessels re-assessed if previously calculated using an assumed passenger weight of less than 75 kg per person. It is at http://www.mcga.gov.uk/c4mca/mcga-mld-page.htm?textobjid=0B977806C138BC7A information supplied by Andrew Sillitoe

The Energy Institute has a Safety Information Bulletin on the topic. It is at

http://energyinst.org.uk/humanfactors/sib

It can also be downloaded from here

* SIB5.pdf:

From Paul Drouin: The Transportation Safety Board of Canada has just published a report that questions the testing standard, (both Canadian and SOLAS) used for the approval of liferafts. The weight (mass) of the occupants was one of the factors TSB wishes the authorities to re-evaluate. Presently, 75kg is the norm. One of the ''messages'' in the report is in the form of a Safety Concern and is as follows;

4.3.2 Standard Mass Determination

Statistics show that more than half of all males over 20 years of age in Canada and the United States have a mass of at least 80 kg. A key criterion to evaluate the performance of a lifesaving device is based, as in the case under review, on a less-than-average value. Although TC has addressed this issue in conjunction with the United States and Sweden at the IMO, it is undetermined at this time if a new standard mass will be agreed upon, or if it will be adequate. It would be logical that a lifesaving device be tested at a higher-than-average mass to create a margin of safety for the majority of users. Decisions such as these should be based on statistics and on the application of rigorous anthropometrical methodology. As the average weight of individuals increases, ''standard mass'' is becoming a concern for the air transportation industry as well. Subsequent to the fatal crash of Georgian Express Flight 126 in January 2004, the TSB recommended that TC re-evaluate the standard weights for passengers and carry-on baggage, and adjust them for all aircraft to reflect current realities. Notwithstanding progress being made on this issue, the Board remains concerned that the standard mass currently used in liferaft testing is inadequate, and that a new standard mass may still not be adequate to ensure acceptable performance of lifesaving devices built for target groups such as fishers. The Board will continue to follow developments related to this issue.

You may be interested to peruse the report at; http://www.tsb.gc.ca/en/reports/marine/2003/m03m0077/m03m0077.pdf

From Margareta Lützhöft: In Sweden the weight for people in elevators is now 80kg.

From BrianSherwoodJones^? My personal impression is that the 75 kg is an average, which may be the right value to use for stability and load tests where there are very large numbers of people, but not for smaller groups. I have not found where that average comes from yet. The calculations by Qinetiq referred to seem a little odd to me. Calculating probabilities is what percentiles is for, I think. The point about specific groups (e.g. Sumo wrestlers) using a boat is an interesting one.

From Cliff Baker: Denise and I have discussed this, and here is our offering. The International Life Saving Appliance Code (IMO resolution MSC.48(66), 2003, invoked via SOLAS), Para 4.3.3 "Carrying capacity of rigid lifeafts" requires that "the number of persons having an average mass of 75kg . . . can be seated with sufficient comfort and headroom . . . " No similar assumption is provided for calculating stability (para 4.3.5).

In the same document, para 44.1 "Construction of lifeboats" subpara 4.4.2.2 states that "the number of persons with a lifeboat to be launched by falls shall be permitted to accommodate shall be equal to the lesser of (quoting now from subpara .1) the number of persons having an average mass of 75 kg . . . "

Paragraph 4.4.5.1 states "All lifeboats shall be stable and a have a positive GM value when loaded with 50% of the number of persons the lifeboat is permitted to accommodate in their normal positions to one side of the centerline."

Additionally, Denise did an anthropological study several years ago on the average weight of US offshore workers. She then related the requirements of MSC.48(66) to the findings of that study. She found that the average US offshore workers weighed 20 kg more than that assumed by the Code (above), and there concurrently was a resulting decrease in lifeboat occupancy of an estimated 20%. She also noted a 100 mm wider hip width compared to average US male data. This makes some strong points about the use of anthropometric data. First, subpopulations may vary dramatically from the parent population, as was the case for Gulf of Mexico offshore workers when compared to North American males and the requirement of MSC.48(66). Second, these variations can present significant safety concerns, (as evidenced by the possible 20% overestimation of lifeboat occupancy in the Gulf of Mexico). Finally, where the application of anthropometric data to design can have serious safety implications, particularly in special or unique environments, data verification studies should be seriously considered.

Question from Brian Sherwood Jones: What is to be done in regulatory terms about this? Options seem to be:

1. Push for a much more conservative limit such as 95th percentile of a world population, which for most small boats is going to be extremely conservative.
2. Leave the limits as they are but ask for a warning sign and a procedure which is likely to be very ineffective.
3. Come up with tailored limits which are going to be patchy in implementation.
4. Do nothing other than talk amongst ourselves.

This topic is exactly right for the marine human element community; we need to do our own regulatory impact assessment and come up with some informed proposal for action, based on sound data (and informed user input where we don't have data). Any thoughts?

-- BrianSherwoodJones - 11 Aug 2005