When I first ventured out to the US on business I encountered a suspended scaffold hanging from, what feels like, every roof I drove by. Taking a closer look, the vast majority of these were hanging from two wire ropes. They had the workers secured by their own safety line. Why would you do that? If you can just add two support ropes on either side? Going through the standards I didn’t see any issue.
I’ve had this discussion with some of my good friends, whom I rate to be very knowledgeable on the subject. There seem to be two main reasons for this: Individual safety and the perceived higher cost of investment.
The latter, so it seems has all to do with the former. As the perception of using four wire ropes is perceived as too costly and unnecessary. Why bother with an additional wire rope, when the people inside are covered by fall protection?
Yes, fall protection is always a good measure. But in case of a fall, you’ll have to be rescued within a very short amount of time. If not, the orthostatic incompetence occurring with a suspension trauma can result in death. In brief the blood amasses in your legs and causes your heart to be restricted from pumping blood through to the vital organs, possibly killing you within 30 minutes.
Now according to the ASME A120.1-2008 Paragraph 188.8.131.52 “All persons shall be provided with and shall use a professional fall protection system complying with ANSI Z359.1-1992 (R1999)”. I fully agree. But this is – or at least should be – a last resort, not the end all in terms of providing worker safety.
Under the assumption that the drop-line will provide sufficient security for the workers, the direct cost cut would be two wire ropes with two hoists and two overspeed detection secondary brake systems. If the primary brake fails or the disc slips an overspeed detection device is required to stop and hold the platform within 24 Inches. On a 10 feet scaffold, that’s a long drop. What happens when the wire rope breaks? 24 inches is nowhere near enough to prevent a platform from tumbling towards the ground. And unfortunately it does happen.
So why not opt for two additional wire ropes? The cost immediately doubles and that makes for a valid argument when operating larger fleets of suspended scaffolding. This is taking into account that the basic set remains the same. A hoist, rigged with a secondary safety device that has overspeed detection. But when used with two ropes instead of one, won’t the simpler slack rope detection device be just as safe?
A slack rope detection device, according to the EN 1808:2015, needs to engage within 19.7 inches. And if we compare an average slack rope device to an average overspeed detection device, prices quickly compensate the loss that the double wire rope brings along. A typical device activates at 12 to 14 degrees tilt. With wire rope breakage, a slipping traction disc or failing primary brake, this is automatically triggered.
If we can accept that a European Notified Body carries the same authority as its American counterpart and the safety precautions are similarly structured to ensure occupational safety for the worker. Would it then be possible to offer a Slack rope device as a safe solution when operated with two additional support ropes? Thus allowing for an increase in safety without immediately increasing the cost? I believe it should be open for discussion.