Posted By Merv Newman Martin, I know of an iron foundry where the finishers wear air-fed masks all day apart from breaks and meals. I worked in the plant for about six months while they were implementing the masks and employees were very happy to use them as the previously frequent eye injuries were eliminated. On the nose bleeds, I have known some. For one case of half-mask use medical gave two possible causes : weak veins and excessive breathing resistance due to infrequent changing of filters. The employee was switched to a different job for a month and retrained on respirator use. The problem did not reappear. I did find one engineering shop where air supplied masks were worn for a few hours each day. Some employees complained of dry eyes, sore noses and occasional nose bleeds. It seems that the air came off the plant compressed air system which had a very low moisture content, hence dryness and irritation leading to bleeding. System was changed to a "breathing air" compressor with frequent checks on O2, N2, H20 and hydrocarbon content. Hope this helps

Posted By Merv Newman Air supplied for breathing : air-fed masks, compressed air tanks, ventilation should always come from a source distinct from ordinary compressed air services. you could check with your local fire brigade : what type of compressor do they use for refilling their ba sets, what precautions and tests do they require. I think there is a BS standard on breathing air quality - O2, N2, H20, hydrocarbon limits. Other info source is ; FACTAIR, Ipswich, 01473 746 400 or even the supplier of your air-fed masks.