Here is a paragraph from the Tuska Open Air Metal Festival website regarding safety hahaha;
"TO MAKE THE GOING SAFE AND SOUND!
To make this festival a first-class happening, members of the audience should pay attention to a few details, too.
We act within the law, and have a couple of special regulations as well.
Any kind of dressing-up is encouraged as long as the safety of your gear is taken into consideration. When rushing about in the front row you may harm a fellow celebrant with your nail bracelet. At the gate of the festival area the crew will check your outfit and remove everything considered dangerous, eg. bracelets made of nails. Use common sense in your dressing-up.
Bottles of glass and cans have to be left outside the festival area.
If, however, you should have on you something considered dangerous, there is a rack where to leave your things at the gate"
Here is the link
http://www.tuska-festival.fi/ 
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