Specifying or Approving Discrete TGSIs – Do they comply

  • December 19, 2009
  • Bruce Bromley

As a designer or certifier are the “Discrete TGSIS” you are responsible for comply?

What are discrete TGSIs?
Tactile domes that are individually installed.

Failing tactile ground surface indicators  TGSIs without sufficient luminance contrast


Discrete TGSIs are not referenced in the deemed-to-satisfy provisions of the BCA. See BCA A0.5(b)

Under  BCA Specification A1.3 AS1428, Part 4, 1992, Tactile ground surface indicators for orientation of people with vision impairment, Amdt 1 is referenced. This standard does not reference Discrete TGSIs. Only the unreferenced AS/NZS 1428.4:2002 does.

The key issue with the use of Discrete TGSIs is Luminance contrast, especially with the polished stainless steel type.

Luminance Contrast is the amount of light reflected from one surface or component, compared to the amount of light reflected from the background or base surfaces.

As a reminder the required luminance contrast for TGSIs to the base surface as follows:

  1. Where the dots and bars are of the same colour as the underlying surface of not less than 30% across its entire area
  2. Where discrete dots and bars of not less than 45%
  3. Where discrete dots and bars are constructed using two colours or materials, the raised surface shall have a section that has 60% luminance contrast for a diameter of 24 mm to 25 mm tested as above.

Where does this leave us as Designers, Certifies or Access Consultants?

An Alternative Solution for discrete tactiles should be prepared. However to prepare an Alternative Solution testing A certificate must be provided by a NATA laboratory that is “Accredited” to test them that both the required Luminance Contrast and Slip Resistance complies.