I have read posts here and at other modeling forums dealing with the construction and use of spray booths, and what I've read has become more than a little troubling. From my perspective, spray booths have at least two major purposes: a) to reduce or eliminate the inhalation of potentially toxic organic vapors and paint residues, and b) to reduce or eliminate the potential for fire or explosion. Unfortunately, I feel that in our somewhat hasty efforts to comply with (a), we have signficantly increased the risks associated with (b); I'm not totally sure we've adequately addressed either.
This post is not for the purpose of creating mass hysteria or panic, but for the purpose of addressing a sometimes often overlooked aspect of our hobby: our safety. If, after reading this, you think I am suffering from some sort of delusional paranoia, please feel free to have me committed. I also hope this will open up some good discussions.
OK, some observations and comments:
a. Spray booths should be constructed of non-combustible materials. Chipboard, plywood, particle board, and most plastics are not good construction materials. Steel, sheetmetal, and aluminum are materials of choice. Walls should be smooth. Baffles should also be non-combustible.
b. Installing a baffle forward of the fan is an excellent way to even out airflow throughout the booth. This will keep organic vapors from accumulating in recesses and corners. This also helps prevent--what I like to call--vapor roll-out or backwash (Your booth is on and working "flawlessly", but you still smell the odor associated with that hot thinner you wanted to try.).
c. Filters should be used to trap any organic and inorganic paint residues. They should also be made of non-combustible materials. I don't think the home HVAC filters will work. Most still have paper frames, don't they?
d. Proper airflow is critical for limiting personal exposures and reducing the potential for fires. Remember, the vapors of ALL organic solvents are heavier than air, and it takes sufficient energy to move them up and out. The MINIMUM airflow at the face (the open part of the booth where you spray) should be 100 fpm (feet per minute). The recommended range is 100-150 fpm. Now, let's take it one step further. If your face area is 2' X 2' (4 sq. ft.), then the motor/fan combination needed to maintain the 100-150 fpm recommendation should maintain at least 400-600 cfm (area X velocity = total cfm). This varies, of course, based on distance from the face, placement in the duct system, baffles, filters, etc. (I hope I got this right.)
e. Keep ductwork as short as possible, and free of 90 degree bends. Resistance on the positive pressure (the push) side of the fan increases with duct length and bending. Ductwork should be made of non-combustible materials. The worn-out vinyl vacuum cleaner hose or drier duct ain't gonna cut it.
f. Fans, and their housings, should be made out of non-sparking materials (non-ferrous metals like aluminum). In addition, motors should not be placed in-line within the ducting. Organic vapors (most of which are flammable or combustible) rolling over arcing armatures does not give me warm fuzzies.
g. Regularly clean residues from fan blades and duct work. This will maintain airflow in the booth at optimal efficiency.
h. Don't place electric lights inside the booth for illumination, especially while spraying. Fires don't make for a good painting session.
i. Keep a fire extinguisher within grabbing distance during spray operations.
I know that this sounds like it quickly becomes cost-prohibitive. For me it is. I still paint with the windows open and fans running. From some of the posts I've read, the best thing some folks could do would be to march their booth out to the trash heap, and paint outdoors, or indoors with windows open and fans running. Maybe all the observations are overstated. Please remember these are recommendations from folks who have been in the safety business for years. They were designed to keep industry, homes and families from being burned out. But this is where you come in. With your mechanical/modeling inventiveness, you can come up with great cost-effective and simple solutions. Who knows; maybe we can get some manufacturers to come up with a simple, safe, and affordable spray booth. I haven't done the research; they may already exist!
Thanks for your patience. I know this is long. I'll get off my soapbox now. Flame away...
Gip Winecoff