Safety requirements for powered sliding gates

• Crushing
• Shearing
• Drawing-in
• Cutting
• Entanglement
• Trapping

There could also be electrical, hydraulic and other hazards, depending on the design of the gate and its operating mechanism. Note that the accepted principle when addressing hazards is to design them out where practicable, then provide guards (eg physical guards around hazardous parts of machinery, and safety light barriers to detect the presence of people in potentially hazardous areas) and, finally, reduce any residual hazards to an acceptable level by measures such as warnings and release mechanisms for use in the event of a person becoming trapped. Powered automatic sliding gates do not move particularly quickly but they are heavy and therefore possess considerable momentum when in motion. For that reason, it is important that the gates are designed as far as reasonably practicable to eliminate the mechanical hazards. When it comes to guarding, the designer needs to consider the harmonised standards relating to reaching distances and minimum gaps to avoid crushing. Note, however, that machinery safety standards are not always written with a view to protecting children; for example, the scope of BS EN ISO 13857, Safety of machinery. Safety distances to prevent hazard zones being reached by upper and lower limbs, excludes children under the age of 14 except for upper limbs reaching through openings, whereas it should be assumed that children will have access to the gates and misuse them (eg by attempting to ride on them while they are in motion).

Examples of measures that can be taken to design-out and safeguard against hazards include:

• Force limitation measures to ensure that an obstruction will not experience forces greater than the values specified in BS EN 12453. This applies to the leading edge of the moving leaf and other crushing, shearing and drawing-in points.
• Either a pressure-sensitive strip or a protected infrared beam on the leading edge of each leaf.

• Safety strips on the leading edges of the inside and outside of the guide posts, hardwired to the control box.
• Sheet infill or mesh to protect the gap between the guide posts, both inside and outside. Mesh apertures should be sized in accordance with table 5 of BS EN ISO 13857.
• Infrared safety beams either side of the gate to detect the presence of pedestrians, vehicles and other obstructions.
• Enclose the run-back area of the gate by fencing 1m away from the gate, or additionally use mesh of a suitable aperture size at least 2m high and positioned in accordance with table 5 of BS EN ISO 13857 to prevent hand/arm access.
• Position the run-back line of the gate at least 1m from the external fence, or ensure that the fence is infilled with additional mesh cladding of a suitable aperture size in accordance with table 5 of BS EN ISO 13857 for the length of the gate run-back to prevent hand/arm access.

More detail is provided in standards such as BS EN 12453 and BS EN ISO 13857. Before a powered gate is specified, designed or installed, it is essential that a risk assessment is performed (likewise, a risk assessment can reveal any shortcomings in the safety of existing gates). BS EN 12453 identifies factors that can influence the level of risk and, in particular, three categories of users and four types of control for which the safeguarding at the leading edge can be different (the following is paraphrased from the standard):

• A limited group of people who are trained to operate a gate that is not in a public area;
• A limited group of people who are trained to operate a gate that is in a public area;
• Any person who is free to operate a gate that is located in a public area.

Gate Controls

• Hold-to-run switch located in sight of the gate;
• Impulse switch (press and release to operate) located in sight of the gate;
• Impulse switch not located in sight of the gate;
• Automatic.

Depending on the combination of users and controls, the required safety measures range from nothing to either:

• force limitation and a means to detect a person or obstacle on the floor at either side of the gate; or
• a means of presence detection to ensure that a person cannot be touched by the gate under any circumstances.

Given that most gates are accessible on at least one side by members of the public (passers-by), the majority of powered gates require the highest category of safety measures.

Although the subject of fail-safe controls is covered by the appropriate standards, it is worth highlighting this requirement in this present White Paper for those readers not familiar with control system design. With a fail-safe design, the failure of a safety device – such as an optional sensor or a pressure-sensitive strip – should result in the gate control system defaulting to a safe condition. Such a component failure may be due to damage (from a vehicle collision or vandalism, for example) or a mechanical or electrical failure of the device itself. In the event of a ‘fail-safe’ situation occurring, the gate is likely to cease operating in its normal automatic mode, depending on the design of the control system. While this may be inconvenient for users, it is essential in order to maintain safety at all times. Powered gates will normally have a means by which they can be opened and closed in the event of the power supply being disconnected, but on no account should attempt to be made to bypass any safety devices.

A gate’s safety-related detection devices, such as optical sensors and pressure-sensitive strips, are often vulnerable, so these should be vandal-proofed as far as reasonably practicable. For example, only suitably robust devices should be used, their location should discourage attack, accessible fasteners should be of tamper-resistant types and, if a CCTV system is installed, a camera can be trained on the gate as a further deterrent. More information about the design of powered sliding gates is available in the DHF publication Guide to gate safety legislation and standards (see Further information below).

Installation

In general, the manufacturer will install the gate, as it is only during installation that the gate becomes fully assembled and can therefore be checked and CE marked. It is vital that the gate is installed correctly if it is to perform as intended and with the required level of safety; this includes both the mechanical and electrical aspects, together with any associated access control system. Architects and specifiers are strongly advised to use installers that are accredited by organisations and schemes such as CHAS (Contractors Health & Safety Scheme), Construction Line, Safe Contractors, Secured by Design, and that adhere to an ISO 9001:2008 quality management system.

Documentation

When a new powered gate is installed, it should be CE marked to indicate compliance with the requirements of the Machinery Directive. In addition, the organisation that CE marks the gate (which may be the manufacturer or the installer, depending on the circumstances) should provide an EC Declaration of Conformity showing with which harmonised standards the gate complies, and a set of instrucitons that includes operation, maintenance, checking correct functioning, and residual risks. As part of the CE marking process, a Technical File should have been assembled, but there is no legal obligation to provide a copy of this.

Maintenance

As with any machinery, powered sliding gates require periodic maintenance. Today’s gates are designed for a long, trouble-free life, but Procter Sliding Gates recommends that its gates are serviced annually or every six months, depending on the level of usage and the types of safety device installed. This servicing not only maintains the operating mechanism and guides in good condition but also checks the operation of the safety features. If the site owner/operator does not wish to undertake this work, facilities management companies can sometimes undertake the work or the gate manufacturer can often provide a maintenance service.