Posted By Dave Merchant Restraint is always preferred if possible, and in your case it's possible. Falling into water may sound reasonably safe, but it's a very last-resort approach to safety for a whole heap of reasons (a lifejacket may keep you afloat, but you can break your neck hitting the surface long before the thing inflates). I'd also be bothered about the boat crew - by the sounds of it they're sitting in a confined space while someone above them sprays down cutting waste and interesting fumes. You could also imagine the Murphy's Law situation where the worker falls onto the boat.

Posted By Ron Hunter Or is the "roof" part of the vessel?

Posted By Mitch Daniel, Is the tank already filled with water or is it to be filled for purging? If it is the latter why not scaffold and net internally (before filling) and erect an edge platform and hand rail externally? Also on prefabricated steel housing I have always used recessed tapped block and dynamic eyebolts fabricated into the structure during manufacture to eliminate trip hazards. Mitch

Posted By Mitch Daniel, Got the bit between my teeth now, what about pontoons (I'll send you details) and magnetic lifting block?

Posted By Ron Hunter I wonder if the existing roof is strong enough to take temporary limpet anchor points. I guess you'll have a crane on the job, wouldn't be difficult then to keep these repositioned in advance of the job, following a planned sequence of plate replacement. I think this job is about fall arrest and mitigating the effects of falls, and you'll need a rescue plan in place.

Posted By Mitch Daniel, When discussing this with the client remember the risk hierarchy and that you may find yourself in a position justifying 'reasonably practicable'. Mitch

Posted By Dave Merchant The 'PPE is last resort' argument doesn't strictly apply to work at height, now the WAHR has a system based on the *format* of protection rather than the equipment used to achieve it:- Avoiding the fall risk entirely is better than everything, but in your case is not possible. Collective fall prevention (edge rails) come next, but again are not possible in your case. Then you have PPE in three stages:- Restraint is better than work positioning, which is better than fall arrest. Finally, you have management and training (as for example when using portable ladders). A restraint system, using 'PPE', is vastly safer than anything which uses fall arrest even if it's a collective system - and in your case the water is NOT the safety system. The lifejacket is. The *water* is just another hazard, so your colleague is wrong - you're replacing one PPE system with another, and the lifejacket is a far more dangerous choice. You certainly don't need anchors for every patch you're cutting - a surface up to 50m diameter can easily be worked with three or four restraint ropes fixed to anchors (the same anchors) at the *edges* of the roof, so the worker sits at the centre of a spiderweb of semi-taught ropes - whichever way he tries to move, one rope stops him. If your tank has edge rails you can probably use them to anchor the ropes to, and not even need to have a tested point installed (restraint, by definition, stops anything more than a bodyweight of load on an anchor point no matter what the user does and so has very low anchor strength requirements). There are many devices which allow adjustment of rope length via sliding grips on the (fixed) rope - Rocker, Stick-run, etc., and this technique is used by thousands of people for building repair, telecoms, firefighting etc. It'd probably cost less than £200 for the entire kit, and there'd be no need for anyone to be in the tank (boat or otherwise), as even if the worker threw himself into the opening, the ropes would prevent him from falling more than a foot or two. Pull the string; out pops the welder.

Posted By patrick carr HI What a excellent thread, the information and knowledge there was a pleasure to read. Great work guys regards Paddy