Be aware of blue asbestos in old cinemas

Blue asbestos was often used inside the wall between the auditorium and the projection room in old cinemas due to the risk of traditional nitrocellulose film igniting if the projector jammed and it got stuck in the high temperature light path.

If you break the surface of a wall in an old building and find blue fluff inside, that looks like laundry dryer lint, then be aware that it may be asbestos, seal the hole back up and get it checked out.

It may even be wise to just leave it in place and seal the wall up again, as the act of removing it will result in airborne fibres and the asbestos removal industry is polluted with greedy companies that use cheap "expendable" labour to do the dirty work.

In the past, asbestos was the new miracle fireproof insulating fibre. It was basically a mineral that could be fluffed up into wool and then used to make clothing and fill walls and roof areas.
It was only in the mid 1980's that they realised that it had a terrible health issue, where the fibres can progressively break into thinner and thinner shards of crystal strands, that are so small that the lungs can't purge them out, and form tissue around them instead. They can also get small enough to slice DNA causing genetic issues.

The majority of asbestos that was used (and is still in use) was white chrysotile asbestos. If you've been exposed to that during your life, then you may find it comforting to know that it has a different structure and can usually be expelled by your lungs quite quickly with no lasting effects. But suitable protective measures should be taken if you know you are working with it these days.