There is a concern with the number of reported slip incidents on supposedly Australian Standard compliant Tactile Ground Surface Indicators.
I have discussed testing with Australian Standard- Adam Stingemore and Angela Roennfeldt of AS ME64 committee.
Upon review of the Slip Resistance Requirements (AS 4662 standards) I have some concerns with the slip resistance testing being used to assimilate a standard shoe in the varying wet, dirty and or hot/cold insitu conditions.
I believe the TGSI tiles are often rated to AS/NZS 4586:2004, Appendix A - Wet Pendulum Test Method and or Appendix D - Oil-wet Ramp Test Method. A TGSI skid resistance is usually assessed as a pass if:
AS/NZS 4586:2004, Appendix A, Wet Pendulum Test Method; in part, the testing is reliant on the principle that "the friction characteristics of each specimen shall be assessed by determining the wet dynamic friction between the specimen and the slider of a pendulum swinging in a vertical plane."
The Rubber sliders in AS4586, 3.2.1 General, "shall be 25.4 ±1.0 mm wide and 6.35 ±0.50 mm thick and rigidly backed. The sliding edges shall be square, clean cut and free from contamination. Sliders shall be 76.0 ±1.0 mm long".
Further in AS4586, A4.3.1 General, "When testing other highly profiled surfaces such as tactile ground surface indicators (TGSIs), the general principle is to maximize the amount of contact between the slider and the test surface. For instance testing typically will contact only the top of six domes, in the orthogonal direction."
Note the rubber block (possibly mimicking a shoe tread) is prepared by cleaning and is prepared with abrasive paper (3* swings minimum) and the test is actioned in 20 degrees +- 5oC touching typically 6 truncated cone top surfaces. Note, further testing is not between the truncated cone top surfaces.
AS/NZS 4586:2004, Appendix D - Oil-wet Ramp Test Method; in part, in this test AS4586 D2 Principal, "Two test persons, wearing standard test shoes, are used to determine the angle of inclination at which safe walking no longer occurs, after the pedestrian surface material being tested has been coated with engine lubricating oil. The test persons, each in turn, facing downhill and with an upright posture, move backwards and forwards over the test surface, as they increase their angle of inclination, until the safe limit of walking is reached. The angles of inclination obtained at such limits are used to assess the friction characteristics of the test surface. The mean acceptance angle obtained is used to assess the degree of slip resistance. Subjective influences on the acceptance angle are limited by means of a calibration procedure."
Further AS/NZS 4586:2004, D3.1 Test shoe, states "Style B shoe design S1 in accordance with BS EN ISO 20345 with an outsole on a nitrile rubber base, IRHD hardness 72 +-2 in accordance with AS 1683.15.1 with a profile as shown in Figure D1."
A picture of the Figure D1 shoes is provided in AS/NZS 4586:2004. The test "shoe" tread may more typically resemble that of a nitrile rubber work boot.
The (AS4586) Australian Standards is often the standard the 'manufactures' use to determine if the 'surface' of the Tactile Ground Surface Indicators (TGSI's) are appropriate for the 'Public' environment and thus they inform the intended users (including Councils) if they meet or exceed the Australian Standards for slip resistance.
The AS/NZS 4586 is often used for an TGSI assessment of if the slip resistance is appropriate or not.
I have concerns about the determination of what is an appropriate test for the following reasons:
1. The AS/NZS 4586:2004, Appendix A, Wet Pendulum Test Method is being used to asses 'many shoe tread types' and the tests preparation includes the test rubber slider be cleaned, prepared with abrasive paper and tested at 20 degrees +- 5oC. i.e.
· The abrasive resistance provided by a prepared 'test rubber slider' to a 'typical shoe tread' may vary,
· The cleanliness expectation of the insitu test and insitu TGSI / path environments.
2. The AS/NZS 4586:2004, Appendix D - Oil-wet Ramp Test Method uses a shoe that may resemble a possible work boot style tread.
· The test tread may be more characteristic of a nitrile rubber work boot tread and not a typical street shoe,
· The shoe tread type (very high quality boot) being used to assimilate a 'test' shoe tread given the public market place shoe variances.
The ongoing TGSI surface slipping concerns may be cause for the appropriate Authorities to review of the Tactile Ground Surface Indicators slip resistance (testing) requirements.
Infrastructure Development Engineer
Glenelg Shire Council PO Box 152 Portland 3305 VIC AU
Phone: (03) 5522 2214
Mobile: 0408 810 341MArmstrong@Glenelg.vic.gov.au
1 AS/NZS 4586:2004, Appendix A.
2 AS/NZS 4586:2004, Appendix A, 3.2.1.
3 AS/NZS 4586:2004, Appendix D, D2.
4 AS/NZS 4586:2004, D3.1 Test shoe.
Registered New Zealand Architect Number 2033
Registered Queensland Architect Number 3531
Finding tactiles to achieve 30% luminous contrast on concrete footpaving is not easy. When I crunch the numbers the answer is "black", or white, for concrete surfaces. "Yellow" fails on dry concrete. Note that most "black" tactiles fail as well.
There seems to be a proliferation of yellow tactiles around Sydney. In the past year I have received submissions from 3 separate contractor Engineers specifying "yellow" tactiles and certifying that they comply with the 30% luminous contrast. When pressed they cannot substantiate their claims. Although one engineer did state that his yellow tactile had a LRV [LF] = 49 which was greater than 30 so it complied. Luminous reflectance value [LRV] is a property of the surface and is not luminous contrast.
The calculations aren't too hard. Two LRV's, for the surface and the tactile, are needed to calculate the luminous contrast. Natural concrete darkens with age so it has a range of luminous reflection [LRV]. It also darkens when wet. Published LRV's for dry concrete ranges from about 23 - 37. Wet concrete ranges from 13- 22. ["Black" asphalt has LRV of about 6.4.]
Using the Bowman-Sapolonski equation [ 125*ILRV2-LRV1I/(LRV1+LRV2+25) ] from AS1428 results in tactiles on concrete needing to have LRV < 5, or LRV > 68, to achieve 30% luminous contrast across the full range of concrete colours. "Yellow" tactiles have LRV's in the range 24- 49 and fail on most dry concrete surfaces.
The LRV of stainless steel cannot be determined in the lab. The results range from about 9-90. However we don't use them because they seem to get very slippery when wet. We don't use ceramic because they are prone to delamination and breakage. We don't use "stick on" because they are prone to lifting at the corners and will delaminate if the concrete is less than 3 weeks old. We don't use concrete because even the black colour fails to provide enough luminous contrast.
Bankstown has standardised on "black" tactiles with LRV < 5 for most light coloured surfaces. The preferred product is FRP - fibre reinforced polymer resin. White with LRV > 68 also complies but is not used as it is not a very maintenance friendly colour.
------------------------------------------- Garry THOMPSON Bankstown City Council BANKSTOWN NSW -------------------------------------------
T: 1300 416 745