Floor_Surfaces_Slip

Floor Surfaces - Slip Resistance

Background
The surfaces over which we push trolleys should be slip resistant so we can work safely. The slipperiness of the floor surface has only a small effect on how the trolley behaves, but it has a large effect on the safety and convenience of the person pushing/pulling that trolley. This note summarises information in Australian Standard AS/NZS 4586:1999, AS/NZS 4663:2002 and HB 197:1999, and makes recommendations as to the choice and use of castors to overcome some of the problems. It also gives advice on keeping the floors clean, so slips are minimised. Full acknowledgment is made of the work of Richard Bowman and the CSIRO.

History of our understanding
It is now clear that no single instrument measurement can provide the basis for deciding whether or not a floor is safe. Old standards felt that a coefficient of friction (COF) of 0.4 separated a good surface from a bad one. In the USA, OSHA recommends a static coefficient of friction of 0.5, and the Americans with Disabilities Act specifies 0.6 on flat surfaces and 0.8 on ramps. A COF above 0.8 does not significantly add to slip resistance. Above 1.0 can impede our ability to walk.

We now realise that a simple decision based on coefficient of friction alone is not sufficient in practice.

When we push trolleys we are affected by:
•	The surface on which we are pushing or pulling the trolley
•	The shoes worn by the user, and the user's personal pushing style
•	Whether the surface is dry / wet / oily / contaminated by food, etc.
•	Whether the surfaces are new or worn, and how worn
•	The inclination of the surface
•	The quality of the lighting / the mental state of the user
•	The configuration of the castors / loading of trolley, etc.

Different ways of describing slip resistance
Absolutely not slippery	Unquestionably safe	Safe for widest range of abnormal stride and pace	Slip highly improbable
Noticeably less slippery	Adequately safe	Safe for hurried stride and pace and minimal attention	Non-slip at very rapid pace
Detectably less slippery	Acceptably safe	Safe for hurried stride and pace and moderate attention	Non-slip at rapid pace
Non-slip	Safe	Safe for normal stride and pace and moderate attention	Non-slip at involuntary pace
Detectably slippery	Marginally safe	Safe for normal stride, pace and attention	Non-slip with reasonable care
Noticeably slippery	Marginally unsafe	Safe for reduced stride and cautious pace	Non-slip with caution
Extremely slippery	Unquestionably unsafe	Safe for short stride and extreme care	Slip highly probable without extreme caution

COF range

Coarse bitumen

This will depend on the test method used as well as the anticipated exposure and traffic requirements

Possibly 0.35 to 0.46 when tested wet according to AS/NZS 3661.1

This will depend on the test method used as well as the anticipated exposure and traffic requirements

Wet ice

Note: The coefficient of friction (COF) is the horizontal force divided by the vertical force. The higher the COF, the less slippery a surface.

The Standard
Previously, the Standard emphasised dry measurements. The new Standard emphasises wet measurements, but allows for 5 different types of testing appropriate to different conditions. The following table gives very approximate correlations, but the standards and the research all emphasise there is little close reproducibility within tests, let alone between different tests, because of the number of variables. This table should not be used other than giving a sense of whether slipping is likely to be better or worse.

Contribution of floor surface to risk of slipping when wet	Wet pendulum with water; 4S rubber of IRHD 96±2		Barefoot ramp with water		Special shoes on ramp with oil; rubber soles of IRHD 72±5
Contribution of floor surface to risk of slipping when wet	Class	British Pendulum No. BPN	Class	Limit of sure movement; inclination of ramp	Class	Threshold of safe walking; inclination of ramp
Very high	Z	< 25	A	³12%	R9	3° to 10°
High	Y	25 - 34	A	³12%	R10	10° to 19°
Moderate	X	35 - 44	B	³18%	R11	19° to 27°
Low	W	45 - 54	C	> 24%	R12	27° to 35°
Very low	V	> 54	C	> 24%	R13	> 35°

Wet area tiles are generally profiled. The amount of profile is measured by smearing the surface with paste, using a flat rule, and measuring how much remains below the surface.

Displacement volume cm3/dm2	4	6	8	10
Assessment Group	V4	V6	V8	V10

The patterning of the tiles etc. needs to be carefully chosen to suit the nature of the contaminants. The amount 'up' gives a longer wearing time, and a better rolling surface for wheels, but the amount 'down' determines the amount of liquids or the size of food scraps etc. that can stay below the true surface. Never use very hard wheels on a profiled surface or the corners of the profiling will be broken. Rounded corners on profiling and a lower surface roughness lowers the slip resistance.

Residential and commercial surfaces are generally smooth, and made from softer materials. The surface should be roughened to at least 10µm on softer vinyls. Industrial and sporting surfaces (e.g. swimming pools) often have hard ceramic surfaces, usually heavily profiled and roughened to at least 14µm. Whether smooth or profiled, the surface should be roughened.

The profiling is so the contaminants (e.g. water, oils, food scraps) can be below the true pedestrian surface, and softer shoe soles can deform and obtain a better grip.

Some examples of how ratings are used	Classification of slip hazard	Minimum displacement value
General workrooms	R9	—
Washrooms	R10	—
Dough preparation	R11	—
Hotel kitchens	R11	Y4
Butter production	R12	—
Poultry processing	R12	V6
Sausage making (raw)	R13	V6
Boiled sausage	R13	V8
Slaughter house	R13	V10

Examples of highly profiled surfaces

Pyramids	Interrupted Pyramids	Tetrahedrons	Interrupted Tetrahedrons
Webs	Interrupted Webs	Cams	Nubs
Interrupted Cams	Interrupted Nubs	Hemispheres	Extract from Australian Standard AS4663

Use of Trolleys When we walk on slippery surfaces, we need to stand upright, and use small steps and extreme care so no sideways forces occur on our shoe soles, leading to a slip. This is not possible when pushing / pulling a trolley. To exert a force on the trolley, there must be an equal and opposite force on our shoe sole. The harder we push / pull, the more we bend over, making it increasingly likely we will slip and fall. Occupational Health and Safety considerations show that with a mixed workforce (including younger/older/females) the sustained pushing / pull force should be limited to 60N (6kg) for long distances. If limited to this, it is usually possible to use trolleys on X/R11 moderate surfaces even if there is slight wetting. However, mixed workforces can, if trained, use up to 216N (21kg) of force to start a trolley. On wet floors (even X/R11 moderate) this may lead to slips. The load on a trolley, the quality of the castors and any inclination of the surface will affect the push effort. Generally speaking, a load of less than 200kg requires less than 100N (10kg) to push it using ball bearing wheels, and this will not cause slips on a X/R11 moderate floor or better. Normally such loads will be carried on trolleys with rubber tyres (of say 50kg to 80kg capacity), and these will not cause damage to floors. Slip resistant mats can be added on critical points. The choice of these needs good advice and preferably trial periods. Slopes Only V/R13 (e.g. coarse bitumen) is suitable for wet ramps, and then only up to 5° max. gradient. When ramps become icy or wet with oil, no gradient can be recommended. Cleaning Floors must be regularly and effectively cleaned in order to be safe. First sweep the floor to remove larger chunks of contamination (e.g. food scraps). Dried oil needs to be brushed with a stiff broom and hot water and detergent. Most cleaning machines are dual chamber, and will not effectively suck up emulsified dirt from micro roughened surfaces. A simple dual system has a chamber for water/detergent and a second for receiving dirty water, but there is no rinsing system and the 'suck-up' of dirty water is not strong enough to evacuate from micro roughness. Emulsified contaminants remain on the roughened surface, where they perish and become slippery. If the surfaces are suitable it is better to scrub floors as normal, then hose the floor and brush the water towards the drains. Clean the scrubber brush, and then re-scrub the surface using hot water and ½ strength detergent. Ensure the sucking mechanism and collection slide are working properly. Refer to Information/Use Conditions/Clean Areas on the Fallshaw web site. Heavily loaded trolleys (and castors) cause more problems:
•	Heavily loaded trolleys often have hard wheels, and these cause damage to heavily profiled floors. Never use cast iron wheels. Nylon or polyurethane of Shore A90 or harder can cause damage to pyramids or tetrahedrons or hemispheres, and must be used slowly and with great care, with not over 600kg on webs or cams. (Remember, damaging the profiles increases slip.)
•	Heavily loaded trolleys cause the operator to lean into the trolley and push with more than 207N (20kg). This leads to slips.
•	Heavily loaded trolleys should only be used on low to very low slipperiness floors. If it is necessary to move from say, V/R13 (e.g. coarse bitumen) to X/R11 (moderate), there should be an intervening surface of Y/R10 for at least 3 metres, as most slips occur when there is a change of surface slipperiness of two grades or more.
•	Heavy trolleys can be towed with a powered tug. If the traction wheels slip it limits movement without causing the operator to slip.
Soft Tread Wheels (High resilience - usually blue in colour) Very soft tyres are frequently used in wet areas on collection trolleys for crockery and cutlery to reduce noise. If heavily loaded, patterned tiles make these very difficult to swivel. Reduce load capacities to half.