I set out to make a spray booth inside the garage, so I bought one of these MiCS5524 VOC sensor breakout boards and hooked it up to an oscilloscope to try out as air quality monitor. It turns out these cheap MEMS devices are ridiculously sensitive to a wide variety of organic solvents used in paints and primers.
Next I bought some carbon air filter media through eBay, rolled up some 1/2" chicken wire into a 4"x2' tube as a sort of intake manifold for the Harbor Freight blower #31810 (sans bag), wrapped the entire filter media roll around the chicken wire tube and plugged the other end of the tube with a piece of cardboard. I let this contraption run inside the closed garage, recirculating the air through the carbon filter.
Around the 1-minute mark on the 10-minute trace shown below I sprayed 2 ml of lacquer thinner into the ~2300 cu.ft. volume of the garage. The carbon filter removes the vapors quite rapidly. Eyeballing the amount of VOC residue measured after ten minutes, I estimate that this works about half as fast as venting to the outside through the man-door with the same blower, before any attempts to seal the leaks past the ghetto filter holder that surely reduce its effectiveness. The blower's stated CFM would recirculate one garage volume in about four minutes, so this all calculates, sort of.
There was only a faint trace of lacquer thinner smell left when I removed my mask after ten minutes. It doesn't seem like the VOC sensor or the carbon media miss anything that the nose can detect.
According to this document, activated charcoal can adsorb up to 25% of its own weight of certain solvents. The $40 mat I bought contains 600g of charcoal, so should be able to pick up about 150g of MEK, toluene, xylene, etc. before needing replaced. This is about half a gallon of high-solids paint, depending on paint, provided one catches the overspray droplets with a prefilter or paper towels.
Aquatic charcoal media are quite a bit cheaper at $1/lb but work much slower as the granules are large, so would require a better filter box design and/or grinding up into powder--not sure what the best way would be to get rid of fine charcoal dust, HEPA filter perhaps, or paint the airplane black lol.
The "Lower Explosive Limits" (LEL) of the most common solvents seem to be in the 1%-2% range, around 12-24 g/m^3. One would need to spray e.g. six pounds of pure toluene into the volume of my garage before creating an explosion hazard. This is a lot of paint, much more than one airplane's worth. The closed system appears quite safe at this rate of removal, unless my math is off.
Let me know your thoughts. While probably too expensive for professional work, to me this approach seems like a promising direction for our one-off airplane painting tasks. It would allow spraying in climate-controlled spaces, with much better control of temperature and humidity, and easier dust control. This combined with the neighbors' happiness will likely justify the extra cost for me.
Next I bought some carbon air filter media through eBay, rolled up some 1/2" chicken wire into a 4"x2' tube as a sort of intake manifold for the Harbor Freight blower #31810 (sans bag), wrapped the entire filter media roll around the chicken wire tube and plugged the other end of the tube with a piece of cardboard. I let this contraption run inside the closed garage, recirculating the air through the carbon filter.
Around the 1-minute mark on the 10-minute trace shown below I sprayed 2 ml of lacquer thinner into the ~2300 cu.ft. volume of the garage. The carbon filter removes the vapors quite rapidly. Eyeballing the amount of VOC residue measured after ten minutes, I estimate that this works about half as fast as venting to the outside through the man-door with the same blower, before any attempts to seal the leaks past the ghetto filter holder that surely reduce its effectiveness. The blower's stated CFM would recirculate one garage volume in about four minutes, so this all calculates, sort of.
There was only a faint trace of lacquer thinner smell left when I removed my mask after ten minutes. It doesn't seem like the VOC sensor or the carbon media miss anything that the nose can detect.
According to this document, activated charcoal can adsorb up to 25% of its own weight of certain solvents. The $40 mat I bought contains 600g of charcoal, so should be able to pick up about 150g of MEK, toluene, xylene, etc. before needing replaced. This is about half a gallon of high-solids paint, depending on paint, provided one catches the overspray droplets with a prefilter or paper towels.
Aquatic charcoal media are quite a bit cheaper at $1/lb but work much slower as the granules are large, so would require a better filter box design and/or grinding up into powder--not sure what the best way would be to get rid of fine charcoal dust, HEPA filter perhaps, or paint the airplane black lol.
The "Lower Explosive Limits" (LEL) of the most common solvents seem to be in the 1%-2% range, around 12-24 g/m^3. One would need to spray e.g. six pounds of pure toluene into the volume of my garage before creating an explosion hazard. This is a lot of paint, much more than one airplane's worth. The closed system appears quite safe at this rate of removal, unless my math is off.
Let me know your thoughts. While probably too expensive for professional work, to me this approach seems like a promising direction for our one-off airplane painting tasks. It would allow spraying in climate-controlled spaces, with much better control of temperature and humidity, and easier dust control. This combined with the neighbors' happiness will likely justify the extra cost for me.