Powered gates: Ensuring powered doors and gates are safe
Powered door and gate safety is not just about the individual components making up the product, but about the way they are combined together to fit a particular set of circumstances, and what is done over time to maintain safety.
At all times a powered gate must respond in a safe way when any person interacts with it. It's design must take into account that foreseeable interactions may go well beyond normal use (eg children playing around or with / on the powered gate), as well as normal wear and tear, and adverse environmental influences, particular wind and rain / snow and other debris that can impair function.
Delivering safety by design and construction
Much is dependent on the way the various component parts (switches, sensors, safety devices, controllers, and motors) are assembled and connected together to respond to the particular environment of use. Safety is usually delivered by a combination of methods, including:
- design to eliminate hazards such as: the gate running away down a slope, coming off tracks / falling over, closing gaps at hinges creating crushing points, access to parts of the mechanism or gaps between the moving leaf and other leaves (including secondary leaves on telescopic gates) or fixed parts (supports, walls, etc), gaps in railings in which heads may get stuck, etc
- the stability and strength of mountings and foundations to adequately resist dynamic forces arising from the weight of the gate as it moves and the effects of wind loadings, so as to minimise adverse effects on actuators and sensing systems
- fixed guarding to prevent / restrict access to drive gears, etc, fencing off the back of sliding gates to avoid shear hazards between the gate leaf and fixed parts, etc
- speed control, including deceleration when nearing the end of travel / rotational movement where crushing hazards may arise
- limitation of forces exerted by moving parts (which may be delivered within the gate motor itself), or in conjunction with external protective mechanisms, including pressure sensitive edges fixed to leading and other edges where crushing/impact hazards exist, to detect and cushion the impact with an obstruction
- non-contact sensors:
- many of these are only designed to prevent a gate closing on a vehicle (note, these beams are not usually high integrity safety devices, in fact they may need to avoid over-sensitive tripping from rain / snow and leaves, and can usually be easily circumnavigated, eg by stepping over). However, they may reduce the probability of contact with the moving gate, particularly if doubled up, eg two beams at different heights, on the 'public' sides of the gate
- safety beams, which as higher integrity 'safety components' may be deployed in some cases to avoid contact with the moving gate(s), but because of cost are less common than pressure sensitive edges
- the way the gate is operated: hold-to-run or automatic (fully automatic or from a starting impulse), and
- the overall behaviour of the system as delivered by the system controller (eg not just stopping when encountering an obstruction, but also backing off at least a short distance to avoid entrapment, because even being held but not crushed can still be hazardous if there is no rescue),
- which is dependent on the compatibility of, and connections between, the various component parts. For example, a gate using a category 2 (as defined by BS EN 954-1 or BS EN ISO 13849-1) controller can deliver only an overall category 2 safety system, even if other components are manufactured to category 3. Furthermore, if the other components are not connected correctly to the controller, the overall safety system may not even achieve category 2, as this requires that a safety-related fault, in any part of the overall safety system, is detected no later than the end of the next gate movement.
- the way the system has been wired and set up during / after installation, including the quality and physical protection of wiring and the connections between all component parts, to resist damage, deterioration and water ingress that may cause the loss of the safety function (eg through short circuits),
- the way the gate responds when any of the safety features are activated, such that no additional risks are created by the system's response (eg when reversing after encountering an obstruction),
- how it is subsequently maintained / set as parts wear and respond to environmental conditions (eg temperature and wind forces, particularly on close boarded hinged gates which may experience high wind loadings that the drive motors may not always be able to overcome).
All these factors must be considered as part of the initial design (through suitable risk assessment), specification and construction, and appropriate information provided in the User Instructions, including on routine maintenance and the nature and periodicity of safety checks. Where force limitation is the safety strategy employed, details of specific force tests should be provided. Lifetime product safety doesn't just depend on design and construction, but the way it is used and looked after, often by others not involved in original design and construction.
Maintaining for safety
Component parts can wear and fail, sometimes catastrophically. Like most machinery, powered doors and gates need to be maintained to remain safe. Powered gates forming parts of workplaces or in common parts of residential complexes will be subject to health and safety law. Owners, occupiers, landlords and managing agents will have on-going responsibilities for the safety of all users and all those who may encounter the gate.
Those undertaking work on powered gates are responsible for what they do, and for leaving the machinery in a safe condition, which may include switching off and isolating from power if it needs to be left in an unsafe condition. Substantial modifications may require re-assessment, in some cases the person undertaking the modifications may need to update conformity assessment marking..
Risk assessment, competence and training
Whilst there may be standard components, even final products, the huge range of locations in which they are installed and variable environmental conditions to which they are exposed mean that most powered gates will be unique products requiring some form of specific risk assessment, both for installation and subsequent use. It is therefore not possible to define standard solutions for safety: each powered gate must be considered individually and holistically, employing suitable risk assessment tools and knowledge / expertise to manage the risks on a case by case basis.
Many organisation offer general training on risk assessment, and within the UK powered gate industry both Gate Safe and the Door and Hardware Federation can provide specific powered gate awareness / competence training.
Those working with powered gates need various competencies depending on their role. Often different members of a team will bring different skills to the job, eg electricians for wiring up and checking the basic safety of the electrical components. In some cases to evaluate component performance specific equipment or instruments may be required. For example, where force limitation is the primary means of safety some form of objective force testing (eg along the lines of EN12445) will be required to ensure the final product as delivered is within safe limits, and to subsequently check the product remains safe. This may require additional specific competencies, and suitable record keeping.
Use of standards for design, assessment and testing
There are a number of current standards which are relevant to powered gates. Adherence to these standards alone may not ensure that all of the mandatory Essential Health and Safety Requirements (EHSRs) of the Supply of Machinery (Safety) Regulations 2008.
In particular hazards may remain with regard to:
- Hinges, because of the way forces measured as specified by the above standards are 'amplified' closer to the pivot point, especially where crushing / trapping hazards have not been removed by design / construction (which may be less easy to avoid when converting existing gates to powered operation). A child fatality incident in 2006 was in part attributed to the design of the hinge area of a hinged gate.
- Shear gaps, especially on sliding gates between moving leaves and fixed parts (or in some cases where leaves pass each other, eg telescopic sliding gates.
- Force limitation, because published research (Mewes & Mauser 2003) suggests that the maximum impact forces permitted by the standards may not always be appropriate for the most vulnerable members of society (children, etc) who may reasonable encounter powered gates (in practice it has been found that where 'safety edges' are appropriately selected and correctly fitted the measured impact forces on both hinged and sliding powered gates can be significantly lower than the maximum levels specified in EN 12453).
- Control systems, because the key standard (BS EN 12453) does not define minimum requirements for safety integrity and reliability in all cases.
The use of any of the above standards by manufacturers for product safety is not mandatory (although products in scope of EN 13241-1 may have to be issued with a Declaration of Performance under the Construction Products Regulation).
Therefore manufacturers will have to show in detail in the technical file for each powered gate how they have designed and constructed the gate to meet the EHSRs excluded from 'presumption of conformity' and be safe for the gate's foreseeable lifetime, taking account of foreseeable misuse, as well as intended use.
1. Mewes & Mauser 2003 Safeguarding Crushing Points by Limitation of Forces International Journal of Occupational Safety and Ergonomics (JOSE) 2003 Vol 9 No 2 177-191.