Will This Metal Grid Increase Risk of Lightning Strike?

Let me put it this way. You make a very good Faraday cage top side, that protects the ants walking under it. Seriously, shape and relative to near objects hight matters most, but I wouldn't step on such a construction positioned on high grounds on a rainy day. Period. S.M.

What material is the flooring?

If it isn't conductive, the people won't be grounded.

I'd worry more about the lighting and sound towers drawing a strike.

I'd also worry about putting 10,000 people in a 20,000 ft. Sq. area.

Where in Ark?

The panels are molded using polypro (non-conductive).

Actually with seating it's 5,000 folks.

So do the metal strips under the panels increase ones chances of lightning strike vs. solid poly panels?

Glen, in the Van Buren, AR office

Well, metal grid on the ground would be more conductive, so I'd have to go with nonmetallic, given a choice.

The liability exposure would be much less.

In your case, I'd go with ppro.

Forget about lightning, as Lyn stated, at best your going to have 10,000 people on 20,000 square feet, one person for every 2 square feet. At worst your going to have 10,000 people on 5,000 square feet, one person for every square 6 inches???? Is this some kind of sardine packing party??

Sounds like an invitation for disaster to me.

No matter how you build your floor you will not eliminate the chance of a lightning strike. Being on a metal non-grounded structure increases the danger and with people packed as densely as you described the chance of multiple injuries or fatalities from a single strike are also greatly increased. There are things you can do to lessen these chances. I suggest you read the following links:

https://www.wildmed.com/blog/lightning-strike-prevention-7-things-to-remember/

http://unitedmethodistinsurance.org/wp-content/uploads/2011/02/MPM-Tips-on-Preventing-Lightning-Strikes.pdf

There are many more pages if you google lightning safety at an outdoor event.

Good luck, be safe.......

Would a building 200' by 100' (20,000 sq ft) with a metal roof be more likely to be struck by lightning than the alternative?

There might be a need to put it into perspective. I've seen metal grandstands used at sporting events for years and I'm sure that you have all seen similar on your side of the world.

Due diligence "Risk assessment" needs to consider all identified concerns and then make appropriate decissions.

My opinion, the risk of lightning (as previously noted) to raised items like lighting towers would be significantly hight than the risk to a horizontal insulating surface over a metal grid (hopefully grounded). The risk of crowd based issues like crushing or heat dissipation for such a concentrated number is significant.

The item you have highlighted is admirable, but only one that needs to be in balance with the total scene.

There are planning regulations for this sort of thing, something the Local Authority in the UK will be keen to enforce if disregarded.

Have a chat with a Planning Officer before finalising the design.

It won't be much of an event if there's only 2-4sqft per person -

Yes. But that is not what matter.

The tallest and spikiest structure (well grounded I expect) will draw the lightning, in all likelyhood.

When the lighning strikes, the real fun begins. When its current reaches the ground, it is spreading out. The center to much further out the momentary voltage difference can be in many million Volts. The "step voltage" difference between your two feet still can be enough to kill you many 10 meters out.

The paragraph is illustrative. Actual lightning data and statistical distributions are produced by Power Utilities. But we do not need them here for a qualitative discourse.

You may bond earthing leads of all services including lightning to it.

As others have indicated, it really depends on what else is arround. Lightning is most attracted to a point charge - as is found on a lightning rod. A bunch of pieces of metal on the ground (simplification of the flooring) are conductive, but are unlikely to create very much point charge. Nearby trees, power lines, or any other conducting and "pointy" structure will be much more likely to get hit.
Of course, in the midwest, there may very well be nothing else around other than open fields. In that case, it is very difficult to tell. I would not say it "attracts" lightning - lightning builds up from the static charge in the atmosphere. I like to picture it akin to rubbing a balloon on one's hair. When the charge builds up, it will discharge through *something* to ground. That something is the best conducting, highest point charge path. If the metal on the ground is the only conducting path around, maybe it would draw the strike. It sounds like it has a heavy insulator over the top (the flooring) - so I am thinking... No.

Not I.

Since you probably have to have $2,000,000.00 USD in liability insurance, you might want to talk to your insurance underwriter.

I'm from Hot Springs.