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Standards up dates and clarification – Fall Arrest/ restraint systems

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images-2Great care is now required when relying on reference to EN795: 2012.It must be understood that this standard referees only to the parts of a fall arrest system considered to be PERSONAL Protective Equipment (PPE) under the European PPE directive.

What does this mean in practical terms?

Products under this code need only be tested and designed for one user, in the UK it is most common for 2 user systems to be specified.

It cannot be assumed that testing for one user means that the system will remain safe for 2 users.

Systems sold for use of more than one user should pass an additional testing to CENTS 16415

EN 795 only covers the testing of certain products themselves as stand alone items.

It offers no guidance on where, what or how these products are attached to for a safety system.

With regard to product testing, scope and use of other components, this is covered by a large number of other specific standards.

There is no standard that covers the strength and design of the installed connections or the actual anchorage to the structure.In its absence these should be verified by rigorous testing and structural verification in accordance with the appropriate structural   design codes.

There is at present no code or scheme to ensure correct competency and training of installers who essentially design the systems.

images-3Treat with caution information you are given with regard to these products, it is a highly specialised area of expertise. Access to competent expertise in can be obtained by contacting the British Safety Industry Federation.

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Are your access provisions truly safe?

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A short video for anyone involved with work at height or purchasing safe access.
Watch to ensure your decisions do not impact on others lives.

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Height Consideration Adverse Weather – Snow

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jan2010 002For your own safety and that of others remember the risks of working at height are greatly increased during adverse weather conditions.

All method statements and risk assessments should be thoroughly revisited and ideally work postponed until conditions improve.

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EN 795 2012

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EN795 1996 has been revised  and replaced by EN 795 2012.

The new standard is designed to ensure consistency EU wide and to eliminate anchors only classified for fall restraint purposes.

It does not cover multiple users, this will be covered by a new supporting technical specification CENT TS 16415, due for publication shortly.

In practical terms:

Existing products should all in time be tested to the revised standards

Specifying just to these codes is not a guarantee that you  will be provided with a complaint installation.

EN 795 2012 relates to the performance of the products in isolation, for one user only.

Once permanently  fixed to the building  anchor points come under the governance of building regulations and the relevant structural design codes.  Compliance with which is the installers responsibility.

If you have any concerns or questions just ask :

enquiries@highwire.info  or  @highwireheightsafety

 

 

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Certification- More than just a piece of paper

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August and the exam result time of year again, with all the usual headlines it brings. A life defining experience on the journey into the adult world. Youthful dreams made or shattered, teenage turmoil and the weight of parental expectation.

Yet few parents would dream of purchasing a certificate. Most parents and indeed their children would find the idea morally abhorrent.

Their child’s grade is a mark of what has been achieved, what can be achieved and what lesson’s should be learnt.

In height safety, certification whether initial, yearly or bi-annual is potentially a matter of life and death. Yet sadly it is frequently viewed as the mere purchase of a certificate.

Certification and yearly inspection of height safety systems include revision of the risk assessments and inspection of the existing equipment, to ensure beyond reasonable doubt that it is compliant with legislation and most importantly fit to save a life.

When we carry out these inspections we look to build long term professional relationships with our clients, to ensure their liabilities are covered. We may require additional information from the original installer. As others may have occasion to clarify original information from us.

Yet frequently when we have serious concerns the original installer offers certification for free, without answering our concerns or even re-inspecting the systems. On other occasions on new build we are told that they do not care if the provisions or proposals work, they only need a certificate at the lowest cost.

I am sure when, God forbid there is an accident and full investigation, the law will look extremely dimly on these practices. Heavy enough penalties are handed out for complete ignorance of the law. Ignoring prior knowledge is premeditated dereliction of duty.

We will continue to raise issues where we have serious concerns over the adequacy of installations, as not to do so could potentially kill someone.

This is the job our reputable clients’ employ us to do and what they expect. We do not find unnecessary fault we are professional, and when we are asked for information to prove our designs we a proud to openly give it.

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Just the weight of a man?

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Summary

  • Yes the load is  significant structurally; as it is a product of the mans’ weight and the speed he is falling at; if we get it wrong the man will fall to the ground and the structure may fail posing a significant risk to others.

  • The speed is determined by gravity and the possible free fall distance.

  •   The potential free fall distance is dependant on the building layout, PPE used and the location of the safety system.

  • With a wire system the distance between supports (or post centres) has a significant effect- The greater the post centres, the greater the wire deflection, the greater the fall distance and potential speed.

  • Due to the number of variables the design  load should be taken as the limiting load for the PPE, 6kN per man/user.

  • Finally the shock absorbing qualities of all components must be taken seriously and be quantifiable, the legislation stipulates that selection of the equipment must best limit injury to the user.

 

The “British Standard” man weighs 15 stone 8 pounds, 100kg on metric measurements. This does not seem a significant load in construction terms.

No one would consider a ball bearing heavy, however very few people would willingly drop one on their toe. Because we all instinctively know that when objects fall they gather speed and momentum, so the further something falls the more force is required to stop it.

 

Given that basic principle of physics let’s put ourselves in the position of a man standing on a roof.

To introduce the basic concept of the loads associated with a fall, I will assume that I have carefully put on my harness and attached this to a basic anchor point using a standard 1.75m lanyard, which will extend by an additional 1.25m once deployed. So the worst case is that I can fall 3m.

  • At 1 m due to gravity I am travelling at 9.81m/s or 22 mph
  • At 1.75m when my lanyard should start to deploy I am travelling at 39mph – the impact load to my body of coming to a sudden halt is already a very uncomfortable thought.
  • Just prior to my fall being arrested after 3m I could be travelling at 66mph.

Now let’s consider I have attached myself to a wire or cable system, I now have the potential to fall a greater distance due to the deflection of the wire. If I assume that the wire supports are no greater than 10m apart I now have a maximum possible free fall height of between 5 and 6 m, with a potential impact speed of 100mph.

Clearly, if the wire is fixed at greater centres the deflection of the wire and  free-fall distance will be greater.

Simplistically

Impact force is a function of  speed and mass

So after falling 5-6 m a 100kg man will exert an impact force of around 5kN equivalent to 500kg or a large motor bike.

Anyone with experience of the construction and maintenance industries would accept that whilst 15 stone 8lb is a reasonable ‘median’ weight, a significant proportion of users are likely to weigh over 16 stone.

Most systems are designed for 2 users and the possibility of a rescue situation must be accounted for.

Lanyards generally start to deploy at just over 4kN and exert no more that 6kN at the point of their connection.

For this reason the  fall load must always be taken as min 6kN per user.

 

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Cable systems the simple facts

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Two men would have no problem at all picking up crate of beer. But if the beer was suspended in the centre of a rope, and they could only pick it up by pulling each end of the rope, this would be far more difficult: and become more and more difficult as the rope length increased.

Exactly the same principle applies with fall arrest.

This basic post is more than adequate to hold the weight of this small worker high above this famous city.However when he is suspended from a string between two posts, it can be seen that exactly the same weight exerts more force on the posts and that this effect increases as the posts are placed further apart.

In this basic desk top example, we are only considering supporting the Lego character, not arresting his fall.

In real life the fall arrest force exerted by a man falling is  6kN as discussed in technical paper 1.

The force required at each end (or reaction) if the wire  is to resist this fall, can be worked out by resolution of forces.

 

It can be seen that reactions, are a tan function of the 6kN force which gives a very narrow range of angles which will be practical.

The angle is dependant on the distance between the posts, the pretension in the wire, the deflection of the wire and lengthening of the wire under load.

 

The distance between the posts has an exponential effect on the force applied as it increases.

Basically  if proper consideration is not given to all the following :

• The post centres
• The cable tension
• The deflection of the cable
• The extension of the cable at impact
• The load absorption of the cable and shock absorbers

The load applied to the structure the system is fitted to can increase exponentially.
For a system with posts at 10 m apart and no shock absorption, and incorrectly tensioned wire, a force  up to and over 30kN – equivalent  to the weight of two 4 wheel drive vehicles will be exerted on the posts.

 

The only way to absorb energy and reduce the load is through calculable and proven energy absorption.

A system with controlled energy absorption and correctly tensioned wire can reduce the load on the post to around 10kN.

Wire systems the facts

STOP !  A cable  system is NOT  class A anchors to EN795 with a wire connecting them!

  • Cable systems are covered under clause 4.3.3 Class C Anchor devices employing horizontal flexible anchor lines. According to the standard the manufacturer must be able to calculate the loads their system will induce, and prove the accuracy of their calculations by testing.
  • All component parts of the system should be CE marked.
  • Never use a manufacturer who is unable to provide  calculations to prove their products, or who states that post centres do not matter.

There are some systems being sold, that quite simply do not work and have not been correctly tested.

 

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