I have a client who has a temporary demountable structure that's got an upstairs. This sort of thing: http://www.hatlapa.de/file.php?ID=956 (just picked from google). You can go upstairs and look out over teh trade show or event. I think there's often a bar up their serving refreshments to weary trade-show VIPs.

He wants to use a staircase that is a slightly spiral (helical) staircase as far as the treads are concerned, but it's set up with straight handrails. So it's a straight spiral staircase. Does that make sense? The bannisters are straight, but the nosing of the bottom step is rotated 60 degrees (in plan) compared to the nosing of the top step. So the going of each step varies - about 230mm at one edge to about 270mm at the other edge. Most of the step noses are therefore not perpendicular to the bannister / handrail.

Leaving aside questions of whether this is aesthetically prudent, what is anyone's view of the safety? Are they going to have people falling up and down it? Is it very unwise? I can't find anything in the likes of building regs or safety guidance about such a situation.

Upstairs is private invitation-only space, incidentally. Numbers are controlled because the staircase is the only access (and therefore only egress in an emergency). There is what is effectively a bouncer at the bottom of the staircase (though I'm led to believe it's normally a sophisticated, polite and pleasant bouncer).

Thanks for your thoughts.

The steps dimensions (rise and going) do indeed meet BS 5395 and also the Building Regs (approved document K). However, they are a configuration that neither document seems to foresee - the steps (risers and treads) are helical, but the parapet and handrail are straight, so steps are not (in general) perpendicular to the handrail.

There are two ways to visualise the situation:

Take a wide helical staircase that does not wind much (just 60 degrees from bottom to top) and suspend two straight handrails above it, then chop away the parts outside the handrails.

Take a straight staircase and rotate the first riser 30 degrees in plan, the second 25 degrees, the third 20 degrees and so on - the middle riser is not rotated, the risers above the middle are rotated the other way with the top riser rotated 30 degrees opposite direction to the bottom, then stretch the treads to fit the risers.

If you don't get it in the sense of don't understand how it can be physically implemented in real 3D space, I don't think I can explain it any more clearly.

If you don't understand why someone would want it, it's to do with the physical configuration of the space - the bottom step has to be rotated relative to the top step, you could do it with a 60 degree landing part-way up the flight (or as first or last step), but that wouldn't fit in the space available - it would jut through the walls (or limit the stair width to be so narrow that it then doesn't comply with width requirements).

It's the fact that the stair meets all the requirements that the standards set, but I don't think it falls within the expectation of the bodies setting the requirements. That is, they don't say "don't do this" only because it never occurred to them that anyone would do it.

It's not illegal, because a BS is not a legal requirement, and building regs don't actually apply because they don't apply to temporary demountable trade show stands. However, the guidance and regulations exist for good reasons, and I don't want to do something that's not technically illegal but fails to satisfy the good reasons.

One option is to just use it and see how many twisted ankles / broken legs / etc occur. If people do fall down it a lot, we could conclude it wasn't such a bright idea after all. However, I'm not sure that's a terribly ethical approach, and breaking the legs of your VIP would-be big clients is apparently frowned upon by the marketing people.

I was hoping someone might have come across a similar situation, or know of any guidance that relates to something similar - for example, there could be a good practice guide that says handrails should always be perpendicular to the nose of treads, or should be at the same angle to the treads over the whole flight, and knowing of such advice from a reliable source might help the decision of whether to go ahead.

Hi Achrn

I work in Live Event Industry and come accross this on almost a daily basis. As you say the structures in the Live Event industry don't met BS Standards but Temporary Demountable Structures. Third Edition Guidance is used. Looking at the photo this seems a generic structure and have seen it many times before. If you want to PM me you can give me a phone.