Because the exposure to the marine environment and motions of a vessel, slips and falls are a significant source of personal injuries in floating equipment, probably substantially greater than most industry groups. Although there are a good number of publications, books and articles written regarding the subject of slip and falls, there are almost none addressing the conditions found in a marine environment, which influence slips and falls.
The generally accepted industry standard is that a static anti-slip coefficient of friction of .50 or above is safe on a dry walkway surface. A value below .50 indicates an unsafe walkway surface. There are some exceptions: The American with Disabilities Act Accessibility Guidelines indicates a minimum Coefficient of Friction of .6 for level surfaces and .8 for ramps. But this guideline should not be used alone when evaluating slip resistance. The influence of the footwear must be included. Also, the above consensus applies to same-level falls in floors that are, for all practical purposes, horizontal.
But the floors or decks on a vessel are rarely horizontal. There is almost always some trim and list/sheer and camber and there are motions.
Furthermore, there are structural deformations created during and after construction, which may affect the anti-slip coefficient of friction, and finally the presence of water on exterior walking/working areas is more common than in land-based facilities.
• The American National Standards Institute (ANSI) has recently created (2001) a standard for work place slips and falls, which was drafted by the American Society of Safety Engineers (ASSE) and is designated as A126.42: "Standard for the Provision of Slip Resistance on Walking/Working Surfaces".
• The American Society for Testing and Materials (ASTM) has a standard method for static coefficient of friction determination: ASTM C 1028-84, and several related standards developed thru many years.
• There are other organizations such as Underwriter's Laboratories (U.L.) that have developed similar standards.
Over the years there have been several approaches to measure the anti-slip coefficient of friction. Various organizations in the USA and overseas have developed apparatus to measure slip resistance. Some measure the dynamic rather than the static coefficient of friction. The hard fact is that different machines may yield different results on the same test surface.
Furthermore, the dynamics of a pedestrian's foot is quite different from the dynamics of a weighted object or a shoe being dragged across a surface.
ANSI standard A1264.2 discussed the slip resistance testing of floors using four approved slip measurement instruments:
• Horizontal pull slipmeter (HPS)
• Brungraber Mark II Portable Inclinable Articulated Slip Tester (PIAST)
• Brungraber Mark I Portable Articulated Sliptester (PIAST)
• Variable Incidence Tribometer (VIT)
The HPS can be used only on dry floors. Despite of the above, it should be mentioned that no two-walkway material industries uses the same method of measuring slip resistance. The resilent tile industry method is different from the commercial floor polish industry.
To attempt to correct this situation, the National Floor Safety Institute (NFSI - Beford, Texas) has developed a tester for wet Static Coefficient of Friction (SCOF) and provides a certification status when the value of the SCOF meets 0.6 or better.
Other factors: There are other factors that have to be kept in mind when dealing with slip resistance. If an object such as a meter (tester) is allowed to remain unmovable on a wet surface for a period of time, adhesion can develop between the object and the surface, resulting in high readings of the static coefficient of friction. Seemingly indicating that the wet surface is more slip resistant than the same surface dry.
Dry Areas of a Vessel
There are at least three factors that affect any coefficient of friction that may be attempted to obtain in any dry area of a vessel, besides other factors in wet areas.
1. Fabrication tolerances of steel or aluminum vessels: The American Society for Testing and Materials has developed a standard guide for steel hull construction tolerances designated as: ASTM F1053/F 1053M-94, which presents permissible deviations, distortions, unfairness and construction inaccuracies in principal strength members in new construction of steel hulls. This guide is restricted to principal strength members and there is almost no provision for local waviness of deck plates. The waviness of deck plates can result in an increase or decrease of the measured coefficient of friction of 5 to 10%, when superimposed to alignment and distortion of the hull.
2. List and Trim/Sheer and Camber: The walk areas of a vessel are intended to be as horizontal as possible when the design condition is being developed. But there are infinite loading conditions, which result in any deck of a vessel not being horizontal at almost anytime. Additionally, most vessels' decks have some sheer and camber. The combination of these factors may affect the measurement of the coefficient of friction by a substantial amount, depending on the location and the type of vessel.
3. Vessel motions: A floating vessel is never at rest. Even alongside the dock, there are constant motions created by wind, currents, waves and wake of other vessels. The roll and pitch motions will affect the coefficient of friction being measured.
Wet Areas of a Vessel
In addition to the factors mentioned for dry areas, there is one more factor of importance regarding slip and fall in wet areas where the amount of water is substantial: hydroplaning. The problem of hydroplaning has been carefully investigated both experimentally and analytically regarding rubber tires on pavement surfaces, but there have not been any mention regarding slip and fall on a wet deck of vessels, although the sole of a shoe in motion will have similar pressure buildup on the sole surface due to his collision with the standing fluid, than the pressure buildup on the tire surface, and therefore, hydroplaning can occur when a person moves fast on a deck where standing water is significant. The marine environ introduces several added factors in the analysis of slip and fall accidents, not normally considered in studies of slip and fall situations in other industries. The generally accepted industry standard that a value of 0.5 and above for the static anti-slip coefficient of friction may be safe on a dry walkway surface, in a non-marine environment, but it may not be sufficiently safe in most marine environments.
Hector V. Pazos, P.E., is a Naval Architect, President, of Ocean-Oil International, a consulting group involved with accident reconstruction and providing Expert Witness services to attorneys. Mr. Pazos can be reached at (504) 367-4072 or (727) 784-8004.