The recent prosecution of a gate manufacturer who did not fit travel stops to a gate they had installed in Leeds, provides fitting motivation to explain the rules surrounding structural integrity. The gate in question came out of its runners and fell, killing a child. This was just one of many falling gate incidents that have caused death or serious injury and resulted in prosecution.
Sliding gates coming out of their runners is the most common failure. Sliding gates must be equipped with physical travel stops that will prevent derailment, both in normal powered use, and when used manually. The manual use element of this provides the greatest challenge as the stops must be strong enough to resist both normal operation and any foreseeable misuse, which might include a user pushing the gate a little too hard or too fast. The travel stops are also needed to provide protection when there is a fault with the limit switch system, in which case the stops will need to be able to control the moving (kinetic) energy and the torque delivered by the drive unit. BS EN 12604 (vehicle gates, doors and barriers) provides structural design safety factors of 2 x total expected load without permanent or detrimental distortion, and 3.5 x expected load without ultimate failure, hence considerable over-engineering is required.
The next most common failure with gates is that of hinge failure leading to the gate falling, in many cases causing death or serious injury. Again, BS EN 12604 provides the minimum acceptable levels of safety. Since 2000, this standard has required that swing and folding gates are constructed so they will not fall if any one single suspension element fails. This requirement was relaxed to some degree when the 2017 version of the standard was published; it now allows that the gate is permitted to fall, but not more than 300mm off vertical, thus allowing the use of catch straps as a control measure. In the UK, it has been a common practice to position gate hinges with the bottom pin facing up and the top pin facing down in an attempt to prevent the gate being lifted off its hinges. In 2014, a 67-year-old woman was killed when an inverted pin palisade gate she was using suffered a fatal bottom hinge failure and fell on her. The coroner investigating her death submitted a ‘regulation 28 report’ to BSI requesting that the relevant standard be revised to specifically prevent the fatal single point failure common to inverted pin hinge designs. In response, BSI duly revised BS 1722-12 (palisade gates and fences) in 2016 to prevent this type of failure.
The likelihood of hinge failure is greatly increased when a gate is able to use contact between the stile and post as the travel stop. This arrangement can generate huge forces at the hinge and has led to numerous death and injury incidents associated with hinge failure. Unless the hinges have been specifically designed to resist such extreme forces, it is unwise and probably unsafe to rely on travel stops so close to the hinge.
Finally, to round off structural integrity, we must also consider the effects of wind load on gates. In particular, where wind action can move a manual or powered gate in manual mode. Again, BS EN 12604 makes a specific requirement that the gate should be able to withstand likely wind loads and be secured against wind action in the fully open and fully closed position. The standard does not require that the gate will actually work (if powered) in high winds, but the gate must remain safe in all expected environmental conditions. Potential wind load should be fundamental to any powered or manual gate design risk assessment.
More detailed explanations of powered gate structural integrity are available in DHF TS 013:2021.
Nick Perkins
dhf Senior Training and Compliance Officer
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