Powered Gate Myth Buster #2

Force test results are evidence of safety

We commonly hear owners and maintainers say: “We know our gates are safe, we have the force test results”.   This could not be further from the truth!

Forces are only measured at specific points on a gate system, essentially these points are where testing can reliably be conducted.  This does not mean, by any stretch of the imagination, that these are the only areas that need to be safe, far from it.

Swing and folding gates are predominately tested at the leading edge; this is actually the point where force will be lowest and is probably the safest part of the gate movement area.  Test results taken at the leading edge need to be assessed to ascertain the likely forces present at other hazards within the movement area.

There are two main hazard types in the movement area of hinged gates:

1. Crush, caused by reducing gaps of less than 500mm, or
2. Impact, where the gate can hit someone in free space without squashing them against something else.

In terms of the potential severity of the hazard, crushing force increases across the gate width towards the hinge.  This is because, although effective speed is decreasing across the gate width, torque will be increasing dramatically.  Conversely, potential impact energy on a person is in effect decreasing with speed across the gate width toward the hinge.

Hence, if there are any reducing gaps in the swept area of the gate, either between the ground, kerbs or at the hinge, care will be needed to ensure that a force of 400N and the requisite force reduction to 150N in 0.75 seconds and to 25N within 5 seconds is not exceeded in the offending reducing gaps.

Where there are no crush potentials in the swept area, a higher force is in fact permitted (1400N), but only providing the force reductions shown above are also achieved.

Where safe edges are used to achieve safe force, providing the same safe edge profile is used at all hazard areas, the test results at the leading edge can safely be taken to indicate safety at all protected areas, because gate overtravel reduces across the gate width.  Where inherent (in the drive unit) force limitation is being relied upon, the same force time limits must be applied but, in this case, it is highly unlikely that protection will be effective towards the hinge area of the gate at crush hazards.  Either safe edges must be deployed, or safe force must be verified directly at the hazard.

A similar situation occurs where force is measured at the leading edge of a sliding gate.  Whilst no tests are carried out at other shear/draw-in points, again, detailed analysis of the results is required to ascertain safe force at the supports and other hazard areas.

So, to sum up, without force measurement, the safe force cannot be known but, unless the test results are correctly assessed against the actual hazards present, safety is still not verified. 

A set of force test ‘passes’ is perfectly possible on a completely lethal set of powered gates.

More detailed explanations of how to verify safe force at ‘other hazards’ and on wind affected gates are available in DHF TS 013:2021.

Nick Perkins

dhf  Senior Training and Compliance Officer