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Specifying the right fall arrest system for each individual


The right fall arrest system for each individual: So much more than a harness that fits

Who remembers the old playground trick question: Which is heavier, a tonne of lead or a tonne of feathers? How about this one: If you drop a hammer and a feather at the same time, which will land first?


The answer to the latter, of course, is that it depends where you are – as proven by Commander David Scott of the Apollo 15 space mission, who conducted this precise experiment on the moon in 1971. He was testing Galileo’s theory from nearly four centuries earlier that objects will fall at the same rate, regardless of their mass, in a vacuum or where the resistance of the medium through which it is falling is negligible. Check out this video beamed back from the Moon 45 years ago (can you believe it?):

The hammer and feather landing simultaneously on the moon’s surface is undoubtedly a ‘Wow’ moment but beyond the science lesson brought to life, the physics at play here has crucial implications in all manner of situations back on Earth.

Feel the force

What is less visible in the famous space footage is that, while the hammer’s acceleration is equal to that of the feather and it hits the ground at the same speed (metres per second – m/s), the hammer has a lot more energy (energy is a combination of speed with mass).

Many people outside engineering and associated fields don’t appreciate the difference between an object’s mass (kilogrammes-kg) and force (kilonewtons – kN) which results from the effect of gravity on that mass and gives the object ever more energy as is speeds up. Yet this difference is the critical factor between a successful fail arrest system and one that could result in serious injury.

A correctly specified fall arrest system needs to account for the mass involved so that the force can be calculated and the system can be tailored to the amount of energy it will have to absorb in operation. At Highwire, we are never simply dealing with a harness and safety lines – a one-size-fits-all approach in these circumstances will not work.

Scientifically tailored solutions

A system that functions perfectly for a 120kg (19st) man could injure a 50kg (8st) woman, for example, if it slowed her fall too quickly. Anyone who has skydived will recall the sensation of being jerked violently upwards as the parachute opened, which was in fact just the extremely fast descent being suddenly slowed – many will have also sported harness-shaped bruising as a memento. The potential for significantly worse injury, including internal damage, in a situation where the fall is unexpected, the person involved is in a far from optimum position and their acceleration must be halted almost instantly, is very clear.

With an increasing number of women working in industries, from engineering and construction to retail and catering, that rely on fall arrest systems under certain conditions, the systems themselves have to be designed and manufactured to cope with a wider range of body mass levels than ever before. At Highwire, this is what we specialise in – precision solutions for the changing market that can be trusted to work effectively whatever the application. The right answer may be slightly different, but our team can advise and deliver the best option for every individual need.

Please get in touch to discuss your fall-arrest requirements

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