Pigs, skin, gut and cut. Whats your method..

[Aussier]

I could except I don't want to buy another pack to do so obviously... Been years without using these ones.

Looking at them again they look just about pristine. I'm comfortable continuing to use them I've decided.

[Kelix]

For you two, I found this from 'Safe-T-Tech' who do respiratory protection gear.

Filter Life Expectancy
It is difficult to determine the exact life expectancy of a filter cartridge. This is because of a number of variable factors. These include the wearers breathing rate, the characteristics and level of contaminant, the length of time a user is exposed to a contaminant. Environmental conditions should also be taken into account such as temperature and humidity which could also affect a wearers breathing rate. Saturated or used cartridges will leak trace amounts of contaminants to the wearer which may be detected via odour, taste, and/or irritation – if a contaminant can be detected by any of these means by the user, then filter cartridges should be changed immediately.

Seems only use causes their filters to degrade, no mention of time passing doing it.

[Oldbloke]

These are slightly different to a cartridge filter but the same should be true. I would use them, better than nothing. No use to you sitting in the shed.

[Aussier]

Thanks Kelix.

Yeah OB, going ahead with them.