During my journey as a woody journo HSE kindly supplied me with a forest sized raft of bumf on this subject and, it turns out, every bit of research has been garnered within a sealed, factory environment with workers doing 8 hour stretches of exposure 5/6 days a week. When I pressed them about a man turning in a shed or garage for 2 hours, once a fortnight I was told they had NO knowledge on the subject and to attempt to extrapolate downwards would be, at best, misleading and downright pointless.
Make what you will of these 'horses mouth' facts before making your own decision on precautions to be taken because there's a lot of self-appointed ... but ill informed... experts out there!!
Have a happy.... and safe.... New Ear everybody
Brian