Fire in the Vacuum System

[bluejay_ca]

Another note today on safety.

I have had fire in my dust collector.
The problem was in my material. It was a laminated panel with spruce on the face and multiple plywood layers beneath. The spruce cut nicely so I just let it go. Wether it was the plywood or the adhesive, a hidden staple, I don't know. The vacuum system and hood I made was set to 1/16" from the surface (based on min Z) so no smoke was visible.
The only warning I had was because I was recircurlating air due to outside temperature. Normally I blow the stuff (and the noise) right outside.
All the more incentive to move the blowers (and the 80+ db) to a metal outside shed!

Not really sure how to prevent this, am I alone on this?

[turmite]

bluejay the commerical units have a detection system and a built in sprinkler system that will mist the dust if a spark is detected. Might be a little messy, but it sure is a lot better than a fire!

Mike

[bluejay_ca]

Thanks for the inspiration. Not sure what the best detection means is. I simply used a temp controller mounted on the top of the tank. Before it melts the valve should open and dump 1 gallon of water through a spray nozzle. P.S. please don't laugh, I didn't have an enclosure and it had to be working before I could finish a current routing project.
I brought a 1/4" line into my cnc cabinet to monitor vacuum but the levels are so low I'm having a hard time with it. Anyone seen a sensor which will work in the 1-5 range. Air flow is critical to me because I have removed my router's fan and rely on the vacuum for cooling. Maybe a mechanical flow switch would be better hmmmm.

[Geof]

For your sprayer heads you could look into the heads used in building sprinkler systems. One style is fully pressurized all the time and has a fusible block that melts at a low temperature to automatically start the flow. If you have a water tank pressurized from an air tank then your system will work even if the electricity has been cut.

[keebler303]

A sprinkler head would be fine, they dump several gallons a minute in a normal system. I don't think its necessary to use air to pressurize the water, after all, if the electricity is cut, the router nor the dust collector will be running.

Matt

[Geof]

Originally Posted by keebler303 A sprinkler head would be fine, they dump several gallons a minute in a normal system. I don't think its necessary to use air to pressurize the water, after all, if the electricity is cut, the router nor the dust collector will be running. Matt

If the electricity is cut as a result of the fire due to short circuit opening a breaker it could be a problem. I am a believer in overkill and also Murphy's law .

I suppose having watched a fire that started in a dust collector system go from the first spark to flames several stories high through the roof in about 20 minutes my view is a bit biased.

Actually you don't need a separate air tank you can get water tanks with a rubber bladder separating air on one side and water on the other that are used with well pumps. I think Home Depot has them.

I also forgot to mention in my suggestion that a foam system rather than straight water may be better. You can get better fire suppression with a lot less water.

[ImanCarrot]

Isn't there a real risk of explosion with dusts? I recal sometime ago an issue with flour and air dust which exploded quite violently.

[Bubba]

The detection systems used in an application like this are usually based on either IR and/or UV (with IR being the preferred one). Be prepared to spend big bucks for the detection system. The sprinklers are usually OPEN head controlled by a valve. The problem with temp setting is the particles (read fire) is traveling at a high rate of speed. Therefore, the ductwork and the collector are usually protected. Sometimes, only the collector is protected due to the high velocity of the particles and the problems associated with the weight of the water in the duct works.
A standard 1/2" orifice sprinkler head will put out about 15 gpm at a pressure of 7 psi at the head!
Yes, foam has been used, but again the equipment to make it work is expensive along with the maintenance required for such a system. Other problems associated with it include:
Protein foam STINKS and after a time if not circulated, will gel up like concrete.
AFFF foam in most cases is now classified as a hazardous material as it contains 1% carbobutal (sp?) and must be dispossed of carfully. Non hazardous foam is available, but very expensive and also requires annual quality testing.
HI-expansion foam, well again the costs are going to be quite high.
Other things to be aware of are other governmental regulations about license requirements for designers of the system, installer, annual inspections, backflow prevention, etc.
For a small home system like we are talking here, best would be just a sprinkler in the dust collector controlled by a valve (most likely a manual ball valve) and some form of tempratue detection in the collector. Some might think a smoke detector will work, but many of them will false trip in dusty conditions.

Sorry to put a damper on some good ideas, but these are the facts of life.

[DSL PWR]

Now for a cheap low tech solution. First get the pressure tank like Geof said, then get some poly tubing and snake it thru your collector in fire prone spots. Cap one end of the tubing and hook the other end up to the pressurized water tank. When you get a fire it will melt the tubing, which will let the water start flowing. This doesn't have the quickest response time, but costs pennies, instead of thousands (uv/ir system). The only reason I wouldn't just hook it on to the water line is if you have a false trip (ie: you didn't fasten the tubing well and it rubbed thru) you will have a large mess. If you get a false trip with a pressure tank, you only have so much water to work with.

Even this is low tech there are many high dollar oil and gas facilities that have a fire protection system built on this principal.

[bluejay_ca]

If you look at the picture you will see that I have used a pressurized tank, an expired propane tank to be exact. I have no water source at this location because of freezing. The tank is 1/2 full of a water/glycol mix, under 120 psi air. The temp sensor is located on top of the blue drum, my vacuum collector. The temp sensor's logic was backwards so I added a relay to rectify that. In order for a fire in the vacuum to escape it will have to do so in the upper portion of the drum which will trip the switch and open the valve.
The vacuum exhaust is directed outdoors via a metal pipe (not shown in photo)

[safeT]

You could make sure the dust is collected in a bin that has a conductive bag so that you can ground out the collector. Dust traps oxygen and makes a mini grain elevator explosion if you are not careful. Static electricity especially about in places that are heated due to cold temp ( did you not explain that it was cold several times ) is prevalentn due to dry air conditions. Ground everything and read up on Explosion proofing which is NOT necessary about building something that will survive an explosion but something that will not create an explosion.

When I worked at NASA, someone put a wet paper towel in a microwave. Because the paper towel was made of recycled material, it contain iron from staples. The microwave caught the paper towel on fire after it dried somewhat.

The dust in your particle wood or any cheap wood may contain volatile organics and pieces of metal, dust, oxygen, and so on.

Your blue tank could be a bomb for all anyone knows. Get everything up to spec on ASME asap.

[bluejay_ca]

Here's my solution. No collection. Exhausted outdoors. (I have no neighbours).

The aluminum blower housing I got from a scrapyard for free. The square aluminum housing and both flanges I fabricated and welded myself. I added a window of 1/4" lexan to view a 1/4" screen to catch big pieces.
The motor is a 1 hp, s.f. 1.65, 3400 rpm - from princess auto salvage area $69.99.
The turbine I fabricated from research and tweaked fin angles based upon airflow and current draw.