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Hi Rounder, Yes, I believe it can be reasonably safe, providing the air supply quantity is adequate, as measured at the hood. I would not put in any kind of "in-line" filter. That will only tend to decrease your air flow, which is most important. You should have some kind of basic particulate filter on the compressor intake, however. If your compressor doesn't already have something like that, you can probably put something together that would keep dirt, dust, bugs, etc. from being sucked in and pumped directly into your hood - something like your typical dust mask would accomplish. No, you do not need any type of air monitor, such as CO or CO2 for such an arrangement. Just make sure that your compressor is located in an area where there is no chance that anything bad to breathe is sucked into the compressor intake - such as car exhaust, for example. Your biggest concern should be that your compressor can supply enough air to adequately maintain a positive pressure inside the hood with respect to the surroundings during periods of inhaling. About 6cfm for a hood and 4 cfm for a facepiece are typical values used for an adequate quantity of air. I don't know about a hood because I have never used one, but for facepieces it's easy to verify that the air quantity is adequate. With those, just use your normal length of supply hose and hold the palm of your hand close to the facepiece exhaust opening. You will feel an outflow of air. Make sure you can still feel an outflow of air when you inhale. It will be less during that period but there should still be a noticeable outflow. That indicates that a positive pressure is maintained inside at all times and that no paint fumes or overspray can enter the facepiece, even if the face-seal is less than perfect. A standard air hose can be used between the compressor and the facepiece/hood. I would recommend dedicating one to that purpose so it doesn't get contaminated with anything and capping both ends when not in use. The size and length of hose that will work properly is dependent of the ability of your compressor to overcome the associated pressure drop at the required cfm flow rate. For example, if your compressor has a capacity of 4 cfm at 1 or 2 psig, it will likely not provide sufficient air through 50 feet of 3/8" air hose for your arrangement to work safely. Commercially available units that supply hoods and facepieces through similar air lines are typically rated for the required flow at about 10 psig discharge pressure. If your air compressor is not tankless but has an attached storage tank, you might want to consider the possibility that warm moisture in the tank could provide an environment for biological nasties to develop. Also that rust particles in the tank could become dislodged and carried to your hood. The compressors that are normally marketed to supply breathing air are not only oil-free but also tankless. That's my own opinion. Others may differ.  Rod
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