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Slippery Tactile Ground Surface Indicators

  • 1.  Slippery Tactile Ground Surface Indicators

    Posted 07-09-2015 10:11
    Over the past 10 to 12 years we have installed a lot of TGSI on our pram crossings or kerb ramps to meet disability access requirements.  We have also replaced a lot of the earlier ceramic versions as they proved to be too slippery for some pedestrians.  We have used a wide variety of makes and types but we have tended to use Polytrac, a reinforced polymer concrete tile, for the last 5 years as it seems to have good grip and durability for external use.  However, we still get complaints about TGSI being a slip hazard, wet weather, shoe types and ramp steepness can be factors.  The design of all our TGSI met the Australian Standards when installed but we still get complaints.  The Australian Standard test method is quite complex and expensive to undertake in the field, particularly if you have a lot of TGSI to be tested.  We do pseudo field trials with staff wearing different shoes etc but results are somewhat subjective.  Can anyone assist with the following questions:

    How long do TGSI last before they need replacing?
    How do you determine if the TGSI should be replaced?
    What varieties of TGSI have lasted well in your experience?


    David Elson
    Pro Cert 2


  • 2.  RE: Slippery Tactile Ground Surface Indicators

    Posted 09-09-2015 14:24
    David,

    An interesting topic, which could become far more complicated if we included luminance contrast.......But first, let me register a declaration of interest. As well as being Access Consultants, we also market a range of TGSIs and stair nosings, which includes the brand you mentioned - the PolyTac, marketed by EIGEN TACTILES in Burwood, Victoria, The PolyTac has an Oil Wet Ramp result of R12 and thus should give excellent anti slip results on kerb ramps but more about that later.

    EIGEN TACTILES is headed up by Michael Lim PhD and Dr Lim used to be a materials scientist with CSIRO before starting EIGEN. So he is no mug.
    Michael has previously told me that he has no love for ceramic TGSIs, particularly on slopes like kerb ramps, but councils continually specify them, because of their relatively low cost, since concreters can drop them in on wet concrete and the job's done........You only get what you pay for!

    Before I get to the specific questions, some background. Most TGSIs on the market today would have been tested under AS4586 - 2004 or earlier. The current Standard is AS4586 -2013 and, under the current Standard an extra test incorporating a 3 micron lapping film is included. This is claimed to give a closer interpretation of a worn or polished heel and thus may better reflect the lower slip resistance likely between the two surfaces under wet water conditions. The outcome of the new test is that some pedestrian surfaces may record a lower slip resistance test result than that done under previous versions of the Standard. However, Clause 4.3.3 of the current Standard notes that test results based on the 2004 Standard and issued prior to the 2013 edition remain valid.

    The current Standard, for other than NCC requirements, which is most of council's work, specifies a minimum of  P5 wet pendulum and R12 oil wet ramp on external ramps steeper than 1:14 and that's the majority of kerb ramps.

    Finally, ask the supplier for a copy of their certificate. To your questions -

    How long do TGSI last before they need replacing? How long is a piece of string? In North Queensland we have old acrylic tactiles still serviceable after 14 years - we have recently replaced polyurethane bladed shaft TGSIs which disintegrated under our UV in two years - you can take your pick of the two brands on the market. Stainless steel studs should last a lifetime, if they are not castings and not annealed and therefore rust in maritime climates.

    How do you determine if the TGSI should be replaced? Usually the TGSI will indicate that. Plastic TGSIs without sufficient aliphatic compounds in their mix will disintegrate, 300 x 300mm cork or plastic tactiles, if not properly installed - the most important procedure in any tactile installation - will have their edges lift and cork will tear. And in shopping centres - shopping trolleys will eventually eat them up!

    What varieties of TGSI have lasted well in your experience? Certified 316 stainless steel studs that are not castings - ceramic tactiles on flat surfaces not subject to wheeled traffic, granite tactiles, polyurethane studs with sufficient aliphatic compounds in them to counter UV degradation and polyurethane integrated peel and stick TGSIs made in Australia, if installed correctly. In closing, the question should be asked - what Council is prepared to pay for the granite TGSIs, the studs with expensive aliphatic compounds, when the bottom line is the only criteria?

    Cheers,   

    -------------------------------------------
    Ian Hudson
    Director
    TACTILE ACCESS CONSULTANTS PTY LTD
    AIRLIE BEACH QLD
    07 4946 5333
    040 9976015
    -------------------------------------------


    Pro Cert 2


  • 3.  RE: Slippery Tactile Ground Surface Indicators

    Posted 14-09-2015 14:23

    David,

    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:

    • "Wet Pendulum Test" assessment group = W or better, and
    • "Oil Wet Ramp Test" assessment group = R11 or better.

    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."[1]

    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"[2].

    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."[3]

    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."[4]

    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.

    Regards,

    Malcolm Armstrong

    Infrastructure Development Engineer

    Glenelg Shire Council
    PO Box 152
    Portland 3305 VIC AU

    Phone: (03) 5522 2214

    Mobile:   0408 810 341
    MArmstrong@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.



     

     

     

     



    -------------------------------------------
    Malcolm Armstrong
    Glenelg Shire Council
    PORTLAND VIC
    -------------------------------------------


    Pro Cert 2


  • 4.  RE: Slippery Tactile Ground Surface Indicators

    Posted 14-09-2015 14:20
    Hi

    A guilty verdict relating to slippery surfaces made the news in http://www.odt.co.nz/campus/university-otago/354274/hazardous-building-costs-varsity

    Slippery-when-wet entrance floor are one of the recurring mistake identified in 170 Post Occupancy Evaluations of buildings.

    Lessons learned are used to flag risks within design proposals, to make sure that mistakes are not repeated.


    -------------------------------------------
    Chris Watson, Architect

    Chris.Watson@PostOccupancyEvaluation.com

    New Zealand mobile phone +64 21 158 7874

    -------------------------------------------

    Registered New Zealand Architect Number 2033

    Registered Queensland Architect Number 3531



    Pro Cert 2


  • 5.  RE: Slippery Tactile Ground Surface Indicators

    Posted 14-09-2015 14:22
    Hi,

    Good to hear that others have had the same experience and found a practical solution.

    As the bottom line is an issue I have been required to seek supply, install and maintain quotations, closing in 3 weeks, for all the different types being installed as part of streetscape works,

    I'm after a 5 year guaranteed life and testing to verify the slip resistance with wear.

    Replacement is reactive to breakage of the porcelain tiles (they are rarely installed correctly and the air gap and shrinkage puts tress on the tiles causing them to break easily - kids were using empty bottles to break them!) AND when there are slipping reports.

    In regard to the bottom line there are a few other important factors that should influence the cost decision:
    1. Injury claim costs
    2. Resident/ratepayer satisfaction with the level of service that the tactiles provide (slippery tactiles aren't fit for purpose)
    3. Reduce overall cost, including life cycle maintenance and product life, by spending more on fewer sites.

    The Eigen tactile has been used to replace the porcelain tiles to date, however this is subject to the quotations being sought.


    -------------------------------------------
    Graham Downie
    Pedestrian Facilities Coordinator
    Brimbank City Council
    SUNSHINE VIC
    -------------------------------------------


    Pro Cert 2


  • 6.  RE: Slippery Tactile Ground Surface Indicators

    Posted 15-09-2015 16:56

    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].
    I
    t 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
    -------------------------------------------


    Pro Cert 2