Force-testing

A gate is required to be people safe.

A gate can be declared safe if the force it applies is within limits set by european standard.

Author  ;  Huw Jones

Why do we need to force test?

A machine is required to be safe. Thats the law, and the installer must leave his installation safely operational. This applied to gates, barrier, doors or threshing machines, whether manual or automated.

Force testing is the only way of proving the gate is in compliance with the force test standards, but the standards are not law, and force testing is not the only route to declaring the gate safe.

What are gate risks?

Forces can be split into static or or dynamic, A static force is pressure from a stationary object, like standing a weight on your foot. Dynamic is when an object is dropped on your foot. The dynamic energy is released when an object of mass hits your foot at speed.

Force testing is mainly concerned with the gate acting on a person. Impacting is the dynamic component, while crushing is the static force applied. 

Dynamic and static forces are measured in the force test. The force limitation chart shows how an initial horizontal dynamic force is permitted to 1400N but must have dropped down below 150N in less than 750ms. If the force is vertical, the dynamic force limit is 400N.

The force must then drop down further within 5 secs of the initial contact. This is to ensure the automated gate does not trap the person with the higher force (150N). It is for this reason, on impact with an object, gate automation systems reverse direction within 5 secs.

Hooking, cutting, and drawing in are hazads that are covered in the gate safety blog. 

'Ez'   Entrapment zones - are areas where operation (or failure) could imprison a person in a space with less than 500mm escape route. Standard definition is a bit fatist.  

'C'   Crush zone - is an area where a gate can apply static and dynamic pressure against a fixed or another moving object. Forces are measured at 50mm, 300mm and 500mm gaps.

'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 (including sliding gate wheels), but also between a motor part and the gate or post.

'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 pinch points over 25mm between a moving part and either another moving or a fixed part.

Hooking   is when a protruding moving part could pull a person towards a risk zone. Common on ornamental gates. Design out, or mitigate unnescessary finials, handles, bolts etc.

Cutting   is a risk from sharp edges impacting a person. No gate part needs to be sharp. There is no test for sharpness.

Swing gate risk zones

Crush zone C1 (which also applies to entrappment) needs to be over 500mm beyond S4 from the hinge. Where S4 is less than 250mm, the crush zone needs to be greater than 200mm. If the crush zone is less than the relevant limit you will need to force test the gap.

Crush zones apply to any fixed object, including a photobeam post.

Sliding gate risk zones

Sliding gates have similar risks with the same test limits.

Vertical bars on sliding gates create new risks for drawing in and shear. Crush and impact forces are easier to protect with photobeams either side of the gate. Crush risk is in a narrow colmn either end of travel.

Draw in is a risk in the wheel area, around the toothed rack, and where the gate passes a stationary post on the motor side. 

Where is force tested?

An impact/crush zone test for a closing gap is carried out at three heights. They are 50mm above ground, at half the gate height, and 300mm from the top of the gate (or 2200mm above ground which ever is greatest).

The force must be measured when the gap is 50mm wide, 500mm wide and 1500mm wide (or the maximum gap width, whichever is greater).

If the opening crush zone is below either The opening force is measured at only one height, 1m from the ground, and at a gap of 500mm.

All measuements are take three times to acheive an accurate average. All readings must be recorded as part of the safety certificate.

Force testing against 2nd leaf or fixed post

When is force testing required?

The guidance gives 3 ways in which a gate can be accredited as safe and have the UKCA mark attached.

Operator vigillance is the puts all the rsponsibility on the person operating it who must be in full control and in full sight of all parts of the gate.

Force limited gate automation requires force to be measured and documented. It cannot exert a force considered to be dangerous, ideal for sensitive public locations like schools.

Risk zone monitoring wraps the area of the moving gate leaves in non contact monitoring equipment (basically photobeams). The gate is made safe (usually stopped) if there is any incursion.

Conclusions on force testing

• Force testing is vigorous and onerous. There could be 60 or more measurements, which will take a few hours and need repeating if any changes are required.
• The force test meter is expensive. There are are only a few on the market. They requires annual calibration to remain valid.
• There are other methods of accrediting a gate. There is an extra equipment cost and associated labour, but the result is certain and requires no testing.