Gate safety

      Gate safety

A gate is a machines. It  needs to be declared 'safe'. 

This blog describes the risks an solutions.

See also;

Author  :    Huw Jones

Gate safety methods

First of all, we are only talking about safety of the individual, and by extension, of animals. So anything that could cause injury to persons, even if they are acting rashly, can be considered a safety issue. 

The only rule is that it must be safe, however in the event of an accident, the authorities will look to the guidance published. The 'Law and the machine' article explains who is responsible for the safety of the gate (see  pagelink).

The gate's documentation is all important. It explains what risks have been anticipated, and the measures used to reduce risk. 

The guidance gives 3 ways in which a gate can be  considered safe.

What 3 ways?

1     Operator vigillance

The gate motor will only run while an authorised person has their finger on a run button. This is the dead man's handle approach where the person is in full control and full sight of all parts of the gate.

2     Risk zone monitoring

Essentially, the area in danger of the moving gate is monitored for any person, and the gate is made safe (usually stopped) if there is any incursion.  

3     Force limitation

The gate can only deliver a limited force in areas considered to be dangerous, so even if a person comes into contact with a gate, the force is within safe limits which reduce with time.

AREA - where is the gate?

The european standards also consider the people who might come into contact with the gate, setting higher standards of safety for public areas than on private property.

An automated gate on a school entrance or home for elderly or disabled would be at more risk 

USER - who is operating?

Gate designers are asked to consider who can operate the gate. A gate operated by key or private remote could be considred lower risk if the only persons with access to the key have been trained.

An open button adjacent to a public walkway is a higher risk. Here, any un-trained person could start the gate without due regard for other members of the public who else might be put at risk.

The framework prescribed by European Standards EN12453 and EN12445

The equipment and the user

HOLD TO RUN button control

FIXED CONTROL from a location

REMOTES,     control from an open/close/stop remote

AUTOMATIC control from a sensor without intervention

PRIVATE area

TRAINED user

A

C

C

C+D

PRIVATE area

UN-TRAINED user

C

C

C+D

C+D

PUBLIC area

TRAINED user

B

C

C+D

C+D

PUBLIC area

UN-TRAINED user

C+D

C+D

C+D

The safety devices required by European Standards EN12453 and EN12445

A

Operator present

With automatic resetting control device (eg hold to run push button)

B

Operator present

With manual resetting of the control device

C

Mechanical & electronic 

Contact devices that reduce force in compliance with force test limits, eg edges & encoders.

D

Photobeams 

To detect any obstacles in the area of auto-mated movement

1.    Operator vigilance

A car perfectly embodies a machine controlled by a vigilant operator. Just as well, as it is also in a public area. The driver has passed a driving test (trained user) and pedestrians are advised to use side paths and road crossing points. The car's accelerator is sprung loaded (automatic reset). It could be safer.

In terms of gates, the hold to run button should be in a place outside the area of movement, and the operator must be able to see the whole risk zone. It is possible for a gate to open with A class control and close under B class control. 

2.    Risk zone monitoring

Risk zone monitoring detects objects entering, or in the area of movement before they are at risk from the moving gate. A ring of photobeams around the gate area is an acceptable form of risk management. The ring should not be too far from the area of movement in case a person was within the cordon before movement began. Dual height photobeams and would be safer. Additional force limitation devices should be considered, such as safety edges and force sensing.

Autonomous cars are a risk managers nightmare. A moving object with considerable kinetic energy loose in a public space with untrained operators. The visual scanning sensors are monoptic, relying on artificial intelligence to assess road hazards. Non-contact scanners have no 'category of behavior' rating.

3.    Force limitation

Object sensing after contact with the moving part can only be proven by force testing, which is covered in another article. It is the most difficult to prove compliance with safety standards. Force limitation is best used with the other two methods. 

Mechanical measures

The other three solution are largely to mittigate risks from motorisation. A manual gate or manual door is also a machine that needs to be safe to operate. Consider an unbalanced garage door, stable when it is raised, but capable of delivering a dangerous force if it is lowered out of control. Another example is a sliding gate that can move beyond its supports, then topple over onto the user.

When not enforced, good practice and common sense can become negligence.  Simple measures can mittigate potential risk and play well to the risk averse. 

'Ez' Entrapment zones - are areas where operation (or failure) could imprison a person in a space with less than 50cm escape route. Standard definition is a bit fatist.  

'C' Crush zone - is an area where a gate can apply pressure against a fixed or another moving object over 50cm away.

'D' Draw-in zone - Drawing in is where a body part is pulled into a moving part, typically between a gate and post, or gate and ground. 

'S' shear points - are where a a body part can be injured by two surfaces moving past each other. Think scissors.

'F' finger traps - are small pinch points between a moving part and either another moving or a fixed part.

Swing gate risk zones

Sliding gate risk zones

Who is responsible?

The installer is responsible for ensuring the gate installation (machine) on handover is compliant with directives, and safe when operated according to its instructions and limitations. The installer must fix a CE mark to the system with a unique reference that is also recorded on the documentation. A CE mark indicates that the machine has been certified. Remarkably, unlike other product certifications, this CE marking does not require a third party certification.

In the machine's doumentation, the installer must accurately and honestly declare the risks, and the safety measures he has taken to mitigate risk. The documentation wil include inspection & maintenance recommendations so that the owner can ensure the machine is operated safety, and the puplic are kept safe from risk.

The documentation will include a description of the machine. If a design change was made to the machine that impacted on safety, the person who ammended the design would become responsible.  Documentation becomes self protection for the installer.

The designer as an expert is responsible for a safe compliant design. The designer signs off the work as having been constructed to his design.

The client may wish to take out a regular maintenance contract with the original installer. If the client chooses a different maintenance company, they will still need to follow the installer's schedule, as that schedule is deemed the designers manual ensuring continued compliance.

The ultimate legal responsibility is on the owner or manager, but in the event of a claim, their defense is that they are not experts, and followed the manual.

A maintenance company must leave a system in a safe condition following maintenance, or they face criminal prosecution. In their defense, they need to show they followed the inspection & maintenace schedule, and made no design changes.

A part changed like for like is not a design change. The schedule should detail regular checks, and re-calibration and/or re-testing where required. The schedule should make clear which parts, if replaced, require the system to be recalibrated or re-tested.

Equipment manufacturers only make components for the machine. They are responsible for accurate description, and instructions for safe application of their components.

The application of a component outside a manufacturer's recommendation becomes the responsibility of the machine designer. Equipment manufacturer can only be responsible for the design and manufacture of his part. 

What standards are relevant to gates?

A standard is a document that a producer can measure his work against. Most standards have product safety or excellence at their root. It is in everybody's interest to build to a standard, except maybe the manufacturer. 

A client can request a machine be built to a standard. It could be a condition of an order that the machine should achieve a standard. It might then be considered a breach of contract if the machine was proven not to achieve that standard. A standard is not a mandatory requirement. 

Standards relevant to automated gates are;

• EN 12604:2000, 2017 & 2017+A1:2020 – manual systems
• EN 12453:2001, 2017 & 2017+A1 – powered systems
• EN 13241:2003+A2:2016 – product standard for Construction Products Regulations 2013

Individual parts to the installation will have their own CE mark that refers to a list of directives and standards. Two directives mandatory for operation in the UK are RED (Radio Equipment Directive) for radio devices, and EMC directive for most connected parts. This only concerns the installer who must be sure are parts are legitimately CE marked.

Since leaving the European Comunity, the EN prefix (European Norm) is replaced by BS EN as Britsh Standards have adopted the EN standards without change.                   

Conclusions

• All concerned should share responsibiliy for the safety. Work collaboratively as a team to ensure the end result is safe.
• As a specifier, name the standards, and make them a condition of the contract
• As a purchaser, be sure to get full documentation with a risk statement.
• Read the copious advice online. Read case histories. Understand the risks. Building a safe machine is not difficult.
• Installers, demand high standards from your supplier. They are there to help.
• Be sure your quotation warns that extra safety measures may be required (and paid for). Every gate is a proto-type.
• If your customer insists on design constraints that you consider unsafe, you must not commission the gate. Who so switches it on after an unsafe notice is responsible.