Sent Friday, August 10, 2001

Although we have been told by purveyors of the ramp test in F06 and F13 that the German Ramp Test is the rage in Europe and Australasia, here are a couple of responses from readers on the scene. First, an activist in the UK Slip Resistance Group had this to say as to the status of slip resistance measurement standards in the EU:

We are trying to get rid of the Tortus and only have the TRL pendulum. There is also a draft standard for the Ramp using standard shoes and water.

But there is no promulgated standard for the Ramp anywhere outside of Germany, where it has resided for decades; there is no standard for any Tortus-like device in Europe or the USA, and the only existing standards for the TRL are for tire traction on wet pavement.

When a representative of the Australian standards organization declined to tell me whether the Australian/New Zealand slip resistance standards (for the Tortus II and the TRL) had been promulgated as law or were still in the provisional phase, I asked a knowledgeable newsletter subscriber in Australia if he could answer my question, Here is his response:

The Australian Standards AS/NZS 3661.1-1993 Slip resistance of pedestrian surfaces part 1: Requirements and AS/NZS 4586:1999 Slip resistance classification of new pedestrian surface materials, are not law.

They have not been called up by the Building Code of Australia - 1996 (our Building Regulations) The Building Code of Australia is part of Government Regulations and is the Law. The Building Code of Australia has the power to call up AS/NZS 3661.1 and AS/NZS 4586:1999, but has failed to do so.

Our courts tend to accept the Australia Standards as good practice but the failure to comply with the standards must be the cause of the accident, for example if someone is carrying a parcel with two hands and is walking down stairs that do not have a handrail and falls on the stairs, then the courts agree that the stairs do not comply to the various Standards and Building Code but it was impossible for the person to use the handrail, hence the person who fell looses. Bill, I would be interested in reading the justification of the XL against brand Y test machine -- and why it provides the best predictor of why a person slips on the walking surface.

Here is my answer to his question:

While I was Director of Loss Control for Marriott Restaurant Operations from 1974 to 1985, I had oversight of safety programs for about a thousand retail restaurants across the US, besides two regional themed amusement parks and large food production commissaries on the East and West coasts. I began my work there by doing an exhaustive analysis of the prior full year?s accident experience, prioritizing accidents by frequency of occurrence and severity. I then picked out all of the high-cost cases for detailed reinvestigation to gather the data needed for development of control programs.

Accident Experience
In that process I noticed that fewer than 20% of the units accounted for more than 80% of the costs. By homing in on these high-loss units, it was not difficult to define the major hazards. Smooth hard floors were accounting for most of the slip/falls. No surprises there.

The next step was to identify the floor types in all of the restaurants and track falls by floor material. Our experience agreed with that of Steve Rosen in identification of floors in order of hazard as set forth his original Slip and Fall Handbook which came out a decade later (1983). Rosen ranked hazardous floors in this order:

1. Terrazzo
2. Marble
3. Ceramic tile

He did not mention resilient floors nor make much distinction among types of ceramic tile. Since VCT floors are prohibited in restaurants by most health departments (among other reasons), we did not have much of that in restaurants, but its traction performance is not much different from other smooth hard floors, especially if it was polished in any way.

Terrazzo has the same traction performance as marble, because it is made out of marble chips. It is marble. Terrazzo is a bit more hazardous in use, however, because of visual considerations. Polished marble looks so slippery that pedestrians are actually much more likely to be careful when walking on it. It in effect carries its own "danger" sign. And while terrazzo does not look as slippery, it has about the same traction properties, therefore deceiving most pedestrians into thinking it is safer than it is. When wet, these surfaces can be slipperier than ice.

Ceramic tile comes in many grades, but in restaurant use, nearly all smooth tiles wind up with a coat of polymerized grease in the course of normal mopping procedures so that they all tend to perform about the same as glazed tile, even the natural quarry pavers. Although smooth ceramic tiles can often have their traction properties greatly improved by etching or particle blasting, if normal slop mopping is used for "cleaning," the build-up of the grease film will return them to their original slippery condition in less than a month.

In food service operations polymerized grease will coat any hard surface, if excellent cleaning methods are not employed; but some tiles will perform better than others if a reasonable cleaning effort is made. Therefore the question of tile safety is complicated. For a full discussion of the traction maintenance problem in restaurant operations, see my chapter on "Slips and Falls in Restaurants" in Pedestrian Slip Resistance, or the one by the same title in my Slips, Trips and Falls book.

Where Does the Slipmeter Come In?
While I was trying to determine what the characteristics of a safe floor were in the 70s, I was using a Horizontal Pull Slipmeter, which was said to be the state of the art at that time, and I became aware that it was worse than useless on wet surfaces because of the sticktion problem [see Learning to Speak Technobabble for an explanation of sticktion]. I had learned which were the hazardous floors by accident analysis, which is the ultimate "slipmeter." But the accident prevention practitioner needs to be able to measure traction without waiting for a million people to walk across the floor and then count the bodies. After several false starts, I discovered how to make the XL emulate the action of a walking foot in its manipulation of the hydrodynamic squeezefilm on the interface between the shoe bottom and the floor.

In my early testing I was excited to see that it ranked surfaces about the same way I knew they should be ranked, based on my accident analyses. But I was somewhat concerned because it showed smooth hard surfaces to be a bit slipperier than I thought they really were. Then I discovered that if I used a courser grade of sandpaper than Charlie Irvine had picked (400 grit) for preparing the HPS feet, I got more realistic readings. I had heard Jim Rowland at HSE (the British equivalent of NIOSH) say that they used 80 grit paper to prepare shoes for testing on the SATRA machine. Later Jim Flynn, one of my pioneer users [http://www.j2eng.com/Staff/Flynn.htm], went to a shoe shop and got a basketfull of discarded heels and examined them for wear texture. By experimenting with different grades of sandpaper, he observed that 180 grit paper gave a texture that looked a lot like what he was seeing on worn-out heels.

That was clear enough evidence to me, and I began to supply 180 grit paper with the XL and changed the operating procedure to contain the present sanding protocol, which is the procedure that was used in the round robin workshops where the 12 volunteers produced the finest precision [http://www.englishxl.com/P&B.htm] for any slipmeter study ever. All of the testing was done "in the sunshine" in conjunction with F13 meetings so that all of our adversaries could watch what we did and how we did it. So far, the only criticism they have been able to come up with is that we did it all on the same day so they could watch. All of them refused to participate in the workshop, though they were invited.

OSHA Research
I have participated in two research projects in connection with SENRAC and OSHA 1926 negotiated rule making in which men were able to rank test panels in order of traction performance by walking on them, and the XL agreed with their rankings in both studies. The first project (referred to by OSHA as "English I") is contained as Chapter 13, "SENRAC" in Pedestrian Slip Resistance, and the complete second study ("English II" in OSHAspeak) is available from William English, Inc. [for details see http://www.englishxl.com/OSHA.htm]

The Ultimate Validation
Although there is nothing official about it, and none of the individuals involved has a large enough database to be able to make an unanswerable assertion, my most competent users report that the more they use the XL, the more they believe its output (as an arbiter of what surfaces are safe and which ones are hazardous.) All of the most experienced tribometric consultants in the US are my customers, and the more experienced they are, the more confident they are in its validity.

When I ask them why they say they are so confident in the XL?s validity, they tell me that when they are metering a floor that was clearly hazardous (based on the fall scenario), the XL ranks it as hazardous. One of my heaviest users who does primarily defense work expresses the same confidence. If the XL registers a .20, he advises his clients to settle, and if it registers .50 or higher, he can convince the ladies and gentlemen of the jury the floor was safe. I was interested to hear of a case where he was testing for the defense, and the plaintiff?s expert was also a certified XL user. Lo and behold, the two certified experts testing the same floor on different days got the same results, which made settlement easy.

Unsurpassed Validity
So the validity of the XL is corroborated in the following ways:

1. It ranks floor hazards in the same order as large samples of accident experience;
2. In two research projects for OSHA, subjective ranking by test walkers agreed with the XL's ranking;
3. The experience of the most competent accident investigators supports it; and
4. It is the instrument of choice among the heavy hitters in pedestrian tribometry.

The ability of the XL to relate to actual fall experience arises from its unique action that manipulates the hydrodynamic squeezefilm in a manner similar to the heel of a pedestrianin walking. [For a tutorial on tribometry with the XL, click here]

So There You Have It
The most competent users with the most experience at fall investigations and slipmetering of floors are convinced. The ones who speak for the companies that make a lot of money selling floor materials that are dangerously slippery when wet don?t seem to agree with them. Fortunately most jurors are more objective than the sellers of dangerous floor materials.