A Crash Deck originally meant a temporary scaffolding platform used to stop falling objects during the demolition process. It has come to be associated with possibly stopping a falling person but this is wrong and is in fact dangerous because it implies that if a ‘crash deck’ is installed a worker is safe and this is not the case.
There are only two options for working at height – a work platform such as RhinoDeck or a fall arrest cushion such as AirDeck. If a worker is working on a work platform, he cannot fall. If he falls onto a fall arrest bag, the fall is cushioned and the g force limited. If he falls onto a ‘crash deck’, the fall is not cushioned and the fall is obviously potentially dangerous.
PAS 59 :14 (fall arrest bags) recommends that a falling person is not exposed to a force of more than 14 g. An 80 kg person falling as a dead weight from just 1 metre on to a ‘crash deck’ that yields no more than 2 cms will be exposed to a g force of about 50g. The more rigid the ‘crash deck’ the greater the g force. If the deck only yields 1 cm, the force is doubled to 100g.
To put this into context, in a car crash, a passenger may experience as much as 50G deceleration, and, if secured by a seatbelt could come away with only superficial injuries. At 75G deceleration, the expected fatality rate is 50%. Deceleration over 80G is considered to be always fatal.
For this reason, a ‘Crash-Deck’ should never be considered as an option for protection when working at height and equally a Work platform should never be referred to as a ‘Crash-Deck’ – confusing the two could be deadly.
Click on the falling man to check out the terminal force calculator.
What height would you have to fall from for your terminal force to exceed 80g – almost certain death? For an 80 kg man an un-cushioned drop onto concrete from just 80 cms could result in death.