Laser Fire

[Joe Hillmann]

The fire was in my universal x-660.
It looks like I got pretty lucky. None of the lenses were damaged,the x,y,z all work and the laser still fires. The x belt is melted and so is one of the wheels/bearings on the carriage. The new belt should arrive on Monday and I already have a new set of bearings. The plexi/poly in the lid is also melted but since that doesn't affect how the machine runs I wont worry about that until I get everything else up and running.

The fire extinguisher I used was a dry chemical. It put the fire out with a 1 second blast so the mess from that isn't too bad. I also have a halon fire extinguisher. It is literally leaning up against the laser that had the fire. But in the excitement (panic) I couldn't find it so I grabbed the one on the wall 6 feet away. Then I tried spraying it and forgot to pull the pin, it took a second or two to figure out why it wasn't spraying and then another few seconds to fiddle with the pin to get it out. If nothing else I learned it is very easy to forget very common sense things when you panic.

As far as the part erupting into flame when I opened the lid. I think the flame was burning on the inside hollow area of the jig for a couple minutes before I noticed the flame on the surface of the of the wood part. And the air flowing over from the exhaust was blowing out what few flames were coming out of the cuts the laser was making. When I opened the the airflow stopped and allowed the flame to burn on the top of the wood and since it was already hot from the fire underneath it burst into flames. I don't think having a stronger exhaust would have prevented this, if anything it would have made it worse because it would have allowed the fire inside the jig to continue growing much longer before I noticed it. And then once the fire got to the surface of the wood the extra air that the exhaust provides would have caused the fire to grow much quicker.

The jig I was using allowed me to cut 18x32 inch pieces of plywood by holding the plywood up of the table, the plywood was supported by a plastic grid to prevent the tar on the cuts that happens if I cut directly on the aluminum table. I think it was the plastic that caused the fire. Most of the plastic under the plywood was burned away but only a small maybe 8 inch circle of the plywood burned which makes me think the fire was burning underneath for a while before the wood actually caught on fire.

[Ross Moshinsky]

No. That would be a partial vacuum. Fire can indeed exist in a partial vacuum.



I said "At best, a very strong exhaust will drop the pressure inside the machine by a very small amount."



I don't think so. A laser's exhaust system only works because there is both a path for the air to go out and a path for new air to enter. With any exhaust system you are constantly resupplying the oxygen from outside air. There is no way for the fire to use up the oxygen when the exhaust system is drawing fresh air in. The more powerful the exhaust, the more fresh air is drawn in.

If you had some form of fire suppression system in your laser then I agree, it would be wise to not open the lid. It would also then be wise to turn off the exhaust so as not to continue to supply the fire with fresh air.

Positive pressure = anything over atmospheric pressure
Vacuum = anything under atmospheric pressure.

If you put a simple relative pressure gauge on your laser, it would read negative pressure IE vacuum. I'm not suggesting it's going to read full vacuum. It's incredibly difficult to create a true vacuum situation.

This is about file prevention, not fire extinguishing. Creating a low oxygen environment is the best way to do that. To do that, a larger exhaust system which creates a lower pressure is a great way to do that. It's not a coincidence that most laser fires occur on lasers with larger table beds or with smaller exhaust fans.

[Rodne Gold]

Larger vacuum systems create a much stronger air flow , that might "blow out" the flame much like air assist or blowing out a match does , I think it's that increased "wind" rather than the drop in air pressure that would inhibit fires.

[Joe Hillmann]

Positive pressure = anything over atmospheric pressure
Vacuum = anything under atmospheric pressure.

If you put a simple relative pressure gauge on your laser, it would read negative pressure IE vacuum. I'm not suggesting it's going to read full vacuum. It's incredibly difficult to create a true vacuum situation.

This is about file prevention, not fire extinguishing. Creating a low oxygen environment is the best way to do that. To do that, a larger exhaust system which creates a lower pressure is a great way to do that. It's not a coincidence that most laser fires occur on lasers with larger table beds or with smaller exhaust fans.

I am sorry, but your way of thinking on this is just dangerous. A fire won't burn in a vacuum because it doesn't have any/enough oxygen to burn. An exhaust system is not a vacuum. It is moving air, it would have nearly the same effect as blowing the same amount of air into a fire with an air compressor. Sure having that strong air flow may prevent a fire by blowing it out before it gets big enough to be self sustaining but once the fire starts the exhaust will just add air to it.

[Ross Moshinsky]

I am sorry, but your way of thinking on this is just dangerous. A fire won't burn in a vacuum because it doesn't have any/enough oxygen to burn. An exhaust system is not a vacuum. It is moving air it would have nearly the same effect as blowing the same amount of air into a fire with and air compressor. Sure having that strong air flow may prevent a fire by blowing it out before it gets big enough to be self sustaining but once the fire starts the exhaust will just add air to it.

Sorry, I should have added my last point to the previous post.

The high flow exhaust system creates a lower pressure zone throughout the laser AND creates an environment where fire doesn't want to exist due to the air flow. A low flow exhaust system creates an environment where fire wants to exist because it's like a nice breeze. A high flow exhaust creates an environment where fire doesn't want to exist like a tornado. The combination of the low pressure and violence of the flow will prevent most fires. Try a simple candle test if you don't believe me.

You had your exhaust on and the lid down and it wasn't an environment where flames could exist. You open the lid, increase the pressure, increase the oxygen in the environment, and make it a more hospitable place for fire to exist. The higher flow the exhaust, the less likely for the fire.

[Rich Harman]

Vacuum = anything under atmospheric pressure.

No. That is a partial vacuum. Look it up.

If you put a simple relative pressure gauge on your laser, it would read negative pressure IE vacuum.

Please, please do this and post a video. Any significant pressure difference and your machine's enclosure will buckle and implode. You will first have to seal your machine really well.

I'm not suggesting it's going to read full vacuum.

Right, it won't read anything even remotely approaching a vacuum. The difference in pressure you will measure will have zero practical effect on the amount of oxygen inside the laser.

Creating a low oxygen environment is the best way to do that. To do that, a larger exhaust system which creates a lower pressure is a great way to do that.

No, it just doesn't work that way.

[Mike Mackenzie]

I agree with you rich, If you have a vacuum your top door lids would break and you would not be able to open the top door. The systems are made with fresh air intakes to allow for the proper air flow for the exhaust. You really could not create a vacuum in these systems with the exception of the cutting table and then there is still fresh air coming into the system.

Bottom line is you the operator must be aware at all times what is going on in the system and only you the operator can prevent fires thats it.

[Martin Boekers]

Hmmm interesting thread, so if you have a great exhuast system no need to monitor while engraving? It would make me wonder why
an increased exhauster system wouldn't be required by insurance companies. A few more thoughts, what happens to wood that smolders,
it may not be a fire but is combustuble, like a BBQ grill, I'm sure most of us at one time have opened a lid to a flare up. It seems if
wood is smoldering the increased airflow would feed it. It may not be a flame yet, but it will rapidly turn to one when the lid is opened.

I would shy away from water as we are working in an electrical environment. Any thoughts on a fire resistant blanketto toss over the table?

A few things I think many can learn from this friendly discussion is, Don't open the lid until you are prepared to deal with it,
Have a quality fire extinguiser close, maybe attached to the side of the machine, and last but not least NEVER think it cant happen to you.

I hate that this happened to you Joe, but it a way it has helped us all of us..... If fact I have 3 new hires right now and this will
make sure I go over safety procedures and express it's importance in an event such as this.

[Rich Harman]

A high flow exhaust creates an environment where fire doesn't want to exist like a tornado. The combination of the low pressure and violence of the flow will prevent most fires. Try a simple candle test if you don't believe me.

Except for the bit about low pressure, I completely agree.

A candle can be easily blown out because the rush of air cools the fire. Fire needs three things (the fire triangle) fuel, heat and oxygen. A strong exhaust system or air assist keeps flames tamed by cooling the fire, not by starving it of oxygen. When the lid is raised the strong airflow is removed, along with it's cooling effect, and you can have a flame up.

[David Rust]

Personally, I would suggest against this line of thinking. You may have a partial (slight) vacuum in the chamber, but you're also pulling in fresh air from the shop and racing it across the burning material. Fires burn almost as easily at the top of a mountain as they do at the bottom, so the slight difference in pressure isn't the saving grace you're hoping it would be. That fast-moving air is likely to flare the fire up rather than keep it suppressed. YMMV...

Dan is right, the exhaust systems increases air flow with "very little" to "no" vacuum. I would be very surprised if you could even measure the differential pressure... It's all about evacuating the smoke... You need airflow, not a vacuum. If you have a vacuum that means your inflow of air is restricted... Bad thing...

go with an easily accessible fire extinguisher, and more important Don't Leave The Machine!!

[Dee Gallo]

The best fire prevention is to pay attention to the laser when you are cutting.

AMEN to that, Mike!

[Jim Huston]

A couple of years ago I had a fire - not in the laser itself but some plastic I had cut and taken out of the laser. Laid the srcap on a nearby table and left the room and shut the door. Later I noticed a lot of smoke in the air - went upto the laser room and saw fire when I opened the door. Soon put it out with no perminate damage but added lasering to the list of wait an hour before leaving the building - along with welding and grinding. Be carefull with the scrap!
JimH

[Craig Matheny]

Check out this link to fireade 2000. I have been fighting fire for over 30 yrs and it is the best I have ever seen.http://www.firesupplydepot.com/quick-order-page.html

Albert with all the electronics halon substitute would be the best choice but are costly 100.00+ for a small unit however are we not investing in insurance buy purchasing the extinguisher? Personally if I have a fire I want it out and the least amount of damage not only by the fire but the chemicals used to put it out. Some fire extinguishers are very corrosive and bad for electronics.

So I guess my thought is as often as you need the fire extinguisher why not spend the money on a good Halon substitute. On other point is the cost to re cert your extinguisher every year halon is every 5 years so that lowers your cost again.

[George Brown]

They make halon extinguishers for small airplanes, disposable, rated for 12 years. On the order of $150.

[David Fairfield]

It may feel a bit silly while you are doing it, but it is a good idea to have an occasional fire drill where you drop what you are doing to grab your gear and go through all the motions. That way you can rely on muscle memory. Like Joe says, its easy to slip into a panic when you see your machinery, shop and home potentially going up in flames. My extinguisher is mounted on the wall near the laser where I have easy access without leaning over anything and its high enough up not to be obscured by clutter that piles up deep. Don't laugh

Dave