F2 Laser Fire - Don't leave laser unattended!!!

[John Blazy]

Hi All,

Been a long time, but thought I'd show up with a warning we all need to hear. I was cutting some epoxy-based laminate samples - section only 3" x 14" into dozens of little 3/4 x 2" rectangles. Cut this material many times before, no flame. Calling an "F2" on tornado scale, because it could have been much worse, but still ceiling damage, entire room needs emptied, cleaned, and redone. Went through three large fire extinguishers to get the fire out.

Many contributing factors:

• Running a business, not a hobby, so pressure to get stuff done, hit deadlines etc, always pushes one to do other things during auto machine cycles, oven cycles, curing phases, etc, so I often leave the laser room, but not anymore.
• Lasering small pcs causes lots of concentrated heat / gas buildup within tight area, even though exhaust is always on.
• lasering near an edge.
• No big fire extinguishers immediately near laser, just a small one, and it was too close to laser to grab anyway.

What to change:

• Never leave laser room during operation - Bring small jobs into laser room to do while monitering (shipping, labeling, packing, computor work, etc)
• Make sure blower pre-filter is cleaned often for better exhaust
• keep large extinguisher right at entry door, and more
• replace lid window with tempered, laminated glass instead of plastic like it had. I think it was polycarbonate, which is the most flameproof of all plastics, but still melted allowing flame propagation. Tempered glass would be a great indicator of a fire, because its explosion will be heard across shop. Laminated would keep it together during fire (a little).

LaserFire.jpg

[Julian Ashcroft]

Is that grid what you were cutting or your base? It looks like it's made of plastic.

[Gary Hair]

All good observations but a glass lid would be a bad idea - acrylic and polycarbonate absorb the beam that our lasers generate but glass does not, not fully anyway, so you would open yourself up to a reflected beam exiting the cabinet through the glass. The other thing is that glass would be so heavy that the door would be extremely difficult to open and the shock-absorber lifts wouldn't keep it open.

[John Blazy]

Is that grid what you were cutting or your base? It looks like it's made of plastic.

Its a non-reflective grid from MDF, kindof burns if constant heat, but mostly is a good grid, as the laser does not reflect off it when cutting acrylic (which leaves lines in edge with honeycomb aluminum). I ran steel rods through it for magnet holds.

All good observations but a glass lid would be a bad idea - acrylic and polycarbonate absorb the beam that our lasers generate but glass does not, not fully anyway, so you would open yourself up to a reflected beam exiting the cabinet through the glass. The other thing is that glass would be so heavy that the door would be extremely difficult to open and the shock-absorber lifts wouldn't keep it open.

Totally correct with the weight. I was hoping to work around that with 1/8" temp glass - similar weight to 1/4 lexan. As far as the safety of stray, reflected laser light - not really concerned, as the beam never reflects up with enough intensity to go through glass, as its all reflected down. I think the lid is just CYA for the laser mfrs. Not one operation that I do reflects intense laser light up in a dangerous way. I do agree that glass is pretty much transparent to lasers. .030" Lexan is more opaque to UV and IR than 1/2" glass - tested that back when I was a UV chemist, and tested "opacity" of clear materials over a UV / IR Radiometer (power puck). Laminated glass, however is just as opaque to the beam as lexan / PC, which is my plan. The EVA laminating resin is high heat resistance, high radiation opacity, and thin. Planned to laminate .030" EVA to 1/8" glass (since I have glass laminating ovens and tech). Should be fine. I appreciate your response though.

[Kev Williams]

Sorry for your loss, and very glad it wasn't worse (a friend of mine had a faulty battery charger take out a 10-plex set of garage shops, $10mil in damages, and no insurance )

for what it's worth-- this is a piece of 1/32" thick polycarb, very thin, that I just hit with a propane torch-
While the edges would flare up slightly, I could not make it catch on fire, all it would do was melt--
pcmelt.jpg
And this just came to me as my furnace just kicked on--- a much better indicator of fire (than exploding glass ) would be to install a heat switch, like those installed in furnaces above the combustion chamber to activate the blower... it would be a piece o' cake to mount one right in the plex lid, they require no power, just a couple of wires to trip a relay to set off a loud alarm. Any type of thermocouple switch like used in kitchen ovens should work too...



.

[Doug Fisher]

Sorry about the fire, John! I am glad the fire didn't spread into your structure. About how long would you guess the fire was burning before you discovered it?

We all have stepped away from the laser and just been lucky. It is often so inefficient to babysit a laser! I am looking into camera options where I run a monitor I can watch if I step into the room next door. LightBurn has some camera functionality built into it. A camera inside my machine might actually be better because I am often sitting down and having to turn my head to peer through the vent hole grid on the front of the machine to look for flames.

[Scott Shepherd]

Been there, done that. Except I never left the room. I was sitting next to the machine and had just looked at it. The fire started below the surface so it was gaining strength without my knowledge. Seconds later, it was a fire.

Universal lasers use glass lids with a metal frame.

[John Blazy]

Sorry for your loss, and very glad it wasn't worse (a friend of mine had a faulty battery charger take out a 10-plex set of garage shops, $10mil in damages, and no insurance )

for what it's worth-- this is a piece of 1/32" thick polycarb, very thin, that I just hit with a propane torch-
While the edges would flare up slightly, I could not make it catch on fire, all it would do was melt--
pcmelt.jpg
And this just came to me as my furnace just kicked on--- a much better indicator of fire (than exploding glass ) would be to install a heat switch, like those installed in furnaces above the combustion chamber to activate the blower... it would be a piece o' cake to mount one right in the plex lid, they require no power, just a couple of wires to trip a relay to set off a loud alarm. Any type of thermocouple switch like used in kitchen ovens should work too...



.

Thanks Kev for the idea - great idea on the heat sensor. Was concerned that it would go off wayyy too often with normal use, but hey. Another reason I like my glass idea is because once the lid lexan melted through, the fire spread way more, and hoping glass would stay intact longer, but once it shatters, even with EVA laminate, it still would slump in, opening up for air to breathe.

Sorry about the fire, John! I am glad the fire didn't spread into your structure. About how long would you guess the fire was burning before you discovered it?

We all have stepped away from the laser and just been lucky. It is often so inefficient to babysit a laser! I am looking into camera options where I run a monitor I can watch if I step into the room next door. LightBurn has some camera functionality built into it. A camera inside my machine might actually be better because I am often sitting down and having to turn my head to peer through the vent hole grid on the front of the machine to look for flames.

Thanks Doug! I think it was burning at least five minutes before I saw smoke pouring from the room. Could have been more. Five minutes for a fire is eternity - plenty of time for the animal to eat (Backdraft reference).

Been there, done that. Except I never left the room. I was sitting next to the machine and had just looked at it. The fire started below the surface so it was gaining strength without my knowledge. Seconds later, it was a fire.
Universal lasers use glass lids with a metal frame.

This was my first serious fire. Had at least two before like yours, that I caught - was in the room monitoring it. It builds under the material where you can't see it. Plenty of times have I shot the little fire with water bottle then air hose, then water bottle, etc. Acrylic cuts near edges or tight are the worst. I was cutting these dichroic acrylic pcs and had to space the parts and internal cuts 1/2" from any edge, otherwise cuts within 1/4" of edge seem to love to catch fire. Thin areas get hot quick, coupled with air flow being higher near edge.

21pcCube.jpg

[Scott Shepherd]

Oh, mine wasn't little Did $3,000 worth of damage to the laser. We put a camera in one laser and it's plugged into a 32" monitor that swivels on the wall. We can see it cutting from anywhere in that room. If I'm running the CNC router, I can leave the door to the shop open and see it from about 50 ft away.

[Kev Williams]

one like this should work dandy, on at 120 off at 105, would require nothing more than a small holesaw--
ts.jpg
it will be very rare IMO that the inside of the cabinet would get to 120° in normal use due to ambient air being drawn in by the blower. These sensors come in many temp variations, and many that are adjustable, you could test actual box temps with any thermometer; if it never gets any higher than 85° in the cabinet, get a 90-on switch, pretty much any extra unwanted heat would be found in short order...

A REAL good place to mount one would be right at the blower exhaust exit--

[Rob Damon]

Thinking about a couple of these for inside my laser or similar.

https://stovetopfirestop.com/product/rangehood/

It is magnetic so it will easily attach to metal lid.

[Scott Shepherd]

Universal's also have a temperature sensor with an alarm on them. If the temp raises inside the cabinet, it sounds an alarm. If the 9V battery that runs it goes bad, the machine won't work. If you are trying to make it safer, then looking at what Universal does is probably a good place to start. Metal framed lid with glass and temperature sensors inside the cabinet would get you some level of protection.

[John Blazy]

one like this should work dandy, on at 120 off at 105, would require nothing more than a small holesaw--

it will be very rare IMO that the inside of the cabinet would get to 120° in normal use due to ambient air being drawn in by the blower. These sensors come in many temp variations, and many that are adjustable, you could test actual box temps with any thermometer; if it never gets any higher than 85° in the cabinet, get a 90-on switch, pretty much any extra unwanted heat would be found in short order...

A REAL good place to mount one would be right at the blower exhaust exit--

Thanks for the reference - will get to it. Great location - near exhaust, inside the hose, or the lower pan where hose attaches.

Oh, mine wasn't little Did $3,000 worth of damage to the laser. We put a camera in one laser and it's plugged into a 32" monitor that swivels on the wall. We can see it cutting from anywhere in that room. If I'm running the CNC router, I can leave the door to the shop open and see it from about 50 ft away.

Nice. Need a camera that feeds into my glasses at top corner, like the spy glasses Arnold wore in True Lies.

Thinking about a couple of these for inside my laser or similar.

https://stovetopfirestop.com/product/rangehood/

It is magnetic so it will easily attach to metal lid.

That is a great cordless, simple add in conjunction with all these great ideas. Need to do that.

[John Lifer]

Glass isn't as heavy as you think. My 1300x900 Chinese has tempered glass in both parts of the lid and polycarbonate is within a pound. Opens and closes with no problem. Temp sensor shouldn't go off without a fire unless it is small laser. Probably not a bad idea to put one in.

[Gary Hair]

I'm not sure a sensor by the exhaust would work out so well as the fast moving air would be much cooler than anywhere else. I think I'd rather put it in a corner where there isn't much air moving instead. Just a thought, could be wrong.

Thanks for the reference - will get to it. Great location - near exhaust, inside the hose, or the lower pan where hose attaches.

Nice. Need a camera that feeds into my glasses at top corner, like the spy glasses Arnold wore in True Lies.

That is a great cordless, simple add in conjunction with all these great ideas. Need to do that.