Well nobody is certain, but people have taken them apart and didn't find anything. So I don't believe they have asbestos, but they may be toxic in some other way.
DON'T USE the big coffee-can style masks because they do contain asbestos. But the standard mask should be fine. If you still don't want to use them, you can buy the Swiss 40mm thread gas mask filters.
No they don't, Gas Mask filters are designed not to go bad despite if the lid is unscrewed off, unscrewing the lid of a gas mask filter doesn't have any effect on the gas mask or it's filters.
the C2 Series canister The primary filters
A gas mask with specific filters designed to effectively protect against chlorine gas exposure should be worn to safeguard against its harmful effects. It is important to ensure that the mask fits properly and is in good working condition before use.
primary filters or... The C2 Series Canister
Maska
diphosgene
They use the military varient of the Gp7 gas mask.
It filters out unwanted chemicals. It's also used to filter water like the Brita filters.
A respirator mask with a P100 filter is recommended for chimney sweeps to protect against harmful particles and gases.
Well the evidence I've seen so far seem to indicate that they do not. Several people have posted clips on youtube where they have cut open said filters and found only activated charcoal and several flammable cotton and paper based filter elements. Most asbestos use in gas mask filters seems to have stopped in the late 50's. The GP5 gas masks that were imported into the United States come from the Ukraine and are of late 80's manufacture or newer. Really there is no need to take the risk, since the filters are too old to likely be of use anyway. It would be wiser to purchase a new manufacture filter with standard NATO 40mm threads which are compatible with the Gp5 mask.
Make sure the filters are securely attached
It removes harmful chemicals from the air you are breathing.