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What Should the Slip Resistance of a Bathtub Be?

Bathtubs, in hotels or homes, are in areas where slip accidents can be very serious or fatal because there are hard objects in close proximity that can be easily struck by the head after a slip — the side of the tub, the faucet, toilets and sinks. Bare feet are soft and essentially treadless, and are treacherous on a smooth soapy wet floor. Slip resistance in tubs must be taken very seriously to avoid grievous bodily injuries and deaths.

All bathtubs should be fitted with ADA-compliant grab bars.

Slip Resistance Testing of Tubs

For nine years, the American Society for Testing and Materials had a bathtub-specific safety slip resistant standard (ASTM F462–79) that was so permissive as to be of no use. It was devised with the help of tub manufacturers so that any production tub on the market at the time would pass the slip resistance standard if it had any kind of surface texture other than completely smooth. This is the only previous U.S. standard of which we are aware and we consider it to have been totally inadequate. We know of no other bathtub-specific standards in the USA.

Our research does not reveal any bathtub-specific slip resistance standard in the Australia, Germany, or the United Kingdom, the three countries that are the leaders in the field of pedestrian slip resistance.

The USA is, sadly, decades behind them. ASTM has by their own admission been incompetent in establishing pedestrian traction test methods and safety standards. Its F13.1 committee is largely controlled by  slip and fall “expert” witnesses who are interested in using test methods that can be manipulated to give data favorable to either defendant or plaintiff, depending on who the client is. There exist no official safety standards to be applied to the test results, which gives the “expert” the freedom of choosing one favorable to his or her client of the moment.

The pendulum skid tester is the instrument known to give the most reliable slip resistance test data for pedestrian surfaces. It has been in use since 1970, is a national standard in at least 50 nations and has been endorsed by Ceramic Tile Institute of America since 2001. For barefoot surfaces, pendulum tests are normally conducted using a soft rubber (known as TRL or TRRL) slider, the hardness of which is roughly that of a typical automobile tire rubber or a bare foot.

Pendulum Test Values (PTV) using the soft TRL slider can range from 5 (plain glass) to well over 100 (very rough, aggressive surfaces). The following are some partly relevant minimum safety standards from Australian Standard AS HB 198:2014:

Location or function of areaMinimum wet PTV (soft rubber)

Bathrooms and ensuites in hospital and aged care facilities

35
Hotel bathrooms, ensuites and toilets20
Communal shower rooms40

“Hotel” is somewhat ambiguous because in Australia that can refer to a public house or “pub”. (Until the late 1980s, pubs were forced by liquor laws to provide accommodation and so were accurately called “hotels.”)

Slip Resistance Treatments

Treatments for existing slippery tubs fall into three categories: clear coatings, acidic chemical etches, and abrasion.

Durable clear (transparent) colorless abrasive coatings are available with soft-rubber wet pendulum test value of up to 45. These are suitable for any bathtub surface and are kind to bare feet. Coatings should preferably pass the McDonalds Restaurants test for Sustainable Slip Resistance, meaning that they will retain their wet slip resistance after years of wear. Minimal monitoring is required, assuming that strong abrasive or polishing pads are not used to clean the surface.

For mineral (porcelain) bathtub surfaces, an acidic chemical etch can sometimes be used. The extent of improvement in PTV depends on solution type and strength, and treatment time. Effect on appearance of the surface is minimal. Proper maintenance is required. Slip resistance of representative tubs must be monitored by testing periodically, and remedial action taken if slip resistance has deteriorated.

For non-mineral (plastic or fiberglass) tub surfaces abrasive (e.g. sandpaper) treatment may be effective. Again, effect on the surface appearance can be minimal but periodic monitoring of slip resistance of representative tubs is necessary, again with remedial action as indicated above.

A caveat about periodic monitoring (slip resistance testing): it is important that the tubs tested in a hotel be representative of all of the tubs. If only certain tubs are specified for monitoring, it is possible that the prescribed maintenance will be conducted only on those tubs, making the test results deceptive and not helpful for ensuring safety or providing a strong defense in court proceedings.

Safety Criterion

From the minimum standard PTV values quoted above (20–40) it is not feasible to deduce a single minimum value for a tub. Tubs tend to have soapy water in them, in contrast to bathroom and toilet room floors, and so a higher standard might be expected of tubs. (Stepping over the tub side to the floor without using a grab bar can also be hazardous.) Tub users can be expected to have different behavior than users of communal showers, where more walking is necessary and in some cases horseplay might occur. Thus the minimum of 40 might be unnecessarily conservative for a tub.

A prudent course of action for hotels might be to promptly remediate any tubs with PTV less than 35 if there are complaints about them being slippery. Standards-setting organizations in the USA and elsewhere should address the problem of establishing an acceptable slip resistance standard for tubs and showers.

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