The safe load capacity for a structure has to be determined by a structural engineer. Everyone else is just guessing. As to what the intended capacity was (not necessarily is), you'd have to go back to the original design documents and see what version of what building code was applicable at the time the design was done.
That said, you also need to understand the difference between 'live load' and 'static load'. You must communicate what activity you plan to do on the stage so the structural engineer understands what the loading conditions are. If you do not tell them, they will not know. Most structural engineers have no idea what transpires on a stage.
It is one thing to build a resting structure (piece of scenery) and have it sitting on the stage floor - that dead load that is generally distributed across the footprint of the scenery is usually pretty safe (unless it is made out of thick plate steel).
The part that gets us all into the danger zone is the 'live load'. This is people all moving about and/or dropping heavy objects. If you look at the 'disaster videos' on YouTube of stages collapsing when twenty performers are dancing on a home-built (or inappropriately modified) pit filler or stage extension, what you see is A LOT of weight being applied to the floor in the form of people bouncing up and down (and typically in close synchronization with the others). Have you ever jumped-up-n-down on your bathroom scale? If it doesn't destroy the scale, you'll see peak 'weights' on the scale that are several times what you weigh when you are just standing there. Twenty people at 180 pounds average weight, jumping up an down together, now you have about FIVE TONS of force. Well, your floor better be able to handle that or you'll end-up in the hospital (and/or in court or on the evening news).
Another consideration for the capacity of a platform is how it is supported. For a given platform (all else being equal), if it is supported from underneath at all for corners (or maybe six places if you have middle supports, too), then it can probably hold more load than if it is only supported from one side. When you have a stage apron that is cantilevered out over the orchestra pit several feet, then it starts to behave like a diving board - it bends a little when a lot of load is applied at the edge. A concrete or steel structure (or even a wood structure if properly constructed) can support a fairly heavy cantilevered load, but a home built platform may well fail and break-off under heavy load.
So, we have to ask ourselves several questions:
Why are we placing a bunch of performers out so near the edge of the stage? It is better to keep them back a bit than unreasonably exposing them to the risk of falling off the front of the stage. This is particularly important if there are fight scenes or other ruckus activity - objects in motion then to stay in motion, and they tend to keep traveling in the direction they are already traveling. So if a performer is headed towards the audience and the front of the stage, then you might consider changing the blocking of the scene so it is across the stage rather than towards downstage - this may keep them from falling off the stage and/or landing in the audience's lap should the scene 'not quite go as planned'.
If the stage has been extended by some home-brew structure, has the school had their risk department sign-off on this? Is the school covered in case the platform collapses? If you have a commercially manufactured platform system (Wenger, StageRite, SteelDeck, etc.), has it been assembled per the manufacturer's instructions (with all of the braces and legs installed)? Will you be using it within the manufacturer's guidelines? (is it rated to have 35 students dancing in-time upon it?)
Why do we need to build the stage forward of the original apron edge? I frequently see stages that are so full of clutter (or 'FUEL' as I refer to it) that they can't effectively use the space. Move all of the junk off the stage. I don't care where it goes as long as it isn't blocking a Fire Exit, but GET IT OFF OF THE STAGE. Wow! Now maybe you have enough room to do the scene you want without having to build forward.
If you are placing monstrous scenery downstage, are you blocking the path of the FIre Curtain? If so, you are in violation of the Fire Code. A Fire Curtain must be able to fully deploy to the floor and seal against it. Desks, chairs, platforms, choral risers, couches, tables, monitor speakers, pianos, etc., all need to be placed on one side of the Fire Curtain or the other - but NOT UNDER IT. Move your scenery upstage a bit to unload the apron.
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Erich Friend
Theatre Consultant
Teqniqal Systems
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Original Message:
Sent: 05-28-2017 07:47
From: Rachel Cunningham
Subject: safety regulations
Does anyone know where I can find safety regulations for a proscenium stage, specifically the weight limits for the stage apron above the orchestra pit? Is there a website or spot to look for and does each state have their own or are the rules universal across the country?
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Rachel Cunningham
Elwood IN
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