A standard grating slot is sized for drainage and for the strength of the bearing bars. It is also, unfortunately, sized for a stiletto heel, a cane tip and the front castor of a wheelchair, which is why standard grating on a pedestrian route is a claim waiting to happen.

Heel guard grating closes the slot down and recovers the lost drainage area by using more slots rather than wider ones. The result takes the same water, carries the same load and does not catch what a standard panel catches.

It is specified where the drainage run crosses a walking route: a building entrance, a station concourse, a shopping street, a hospital approach. In those places the grating is walked on by everyone rather than by maintenance staff, and the slot width is a safety decision rather than a hydraulic one.