New project: Fire sensing laser cut out system - and maybe more later.

[Dave Sheldrake]

dan.jpg

Not mine but the owner is a member here and may well be able to tell you about acrylic fires.....

[Scott Shepherd]

I see you save laser fire photos too Dave

[Keith Colson]

Dave, I think that one would have set off a fire sensor! Were they cutting with the paper on the top surface? I just don't get any flare ups at all unless I leave the kindling (top paper) on the acrylic.

[Graham Facer]

Well, I'm pretty sure we can design something to avoid these pictures. That's the goal.

Then I'll set something on fire to test it...

[Dave Sheldrake]

I see you save laser fire photos too Dave

Got 50 or so of them Scotty all caused the same way

Dave, I think that one would have set off a fire sensor! Were they cutting with the paper on the top surface? I just don't get any flare ups at all unless I leave the kindling (top paper) on the acrylic.

It's the down-draft Keith, that accelerates a fire at incredible speed, a bit like a blacksmiths forge in some ways, much of the time it's detritus on the bed or in some cases under the bed. I've been out to some real horror stories over the years where a machine hasn't been cleaned for weeks

[Rodne Gold]

cheapest way , IMO , is to employ a minder and operator. Our operators would get summarily fired if they left a machine unattended, they all know that and its in their employment contract.
GCC has some sort of fire suppression system or warning system called Smartguard

[Gary Hair]

Your website shows almost all of your products to be acrylic. If you are saying that that has a slow spread on fire, you might need to look for the post recently where thin acrylic was cut and caught fire. Acrylic is NASTY as far as fire. Been doing this about 8 years now and acrylic causes me GREAT concern. I'd leave wood long before leaving acrylic, and I cut a lot of acrylic.

I agree, I've never had wood catch fire but I have had numerous times with acrylic. I'm always watching it so it never gets beyond a point where stopping the laser and merely blowing on it won't put it out, but as has been already said, that difference is seconds.

[Graham Facer]

OK I'm definitely raising my goal, a fully automated fire control system with escalating unattended response.

1) Cut laser/alarm
2) 15 sec delay and then fan shut off and full cabinet CO 2 purge followed by re-venting.

and maybe with push button settings for different materials.

Its quite frankly ridiculous that we'll spend tens of thousands for machines that need to be watched like a hawk less they self destruct. Its like having to watch a home furnace all day and night, lest it should burst into flame. I've been convinced that my attitude is hazardous, but I cannot hire a person to watch a machine that is not used full time and I wear enough hats as it is.

And please can we focus this thread on this problem/solution idea. I did not come looking for a burnt out machine thread, I came trying to avoid it.

Scott: Do you have some more details on what you tried (what sensors if you recall, where you had them - even your arduino sketch?).

[Rodne Gold]

Maybe this helps
http://laserprona.com/new/wp-content..._SI-SG-SGX.pdf

[Dan Hintz]

Its quite frankly ridiculous that we'll spend tens of thousands for machines that need to be watched like a hawk less they self destruct. Its like having to watch a home furnace all day and night, lest it should burst into flame. I've been convinced that my attitude is hazardous, but I cannot hire a person to watch a machine that is not used full time and I wear enough hats as it is.

And please can we focus this thread on this problem/solution idea. I did not come looking for a burnt out machine thread, I came trying to avoid it.

My daily driver cost $50k... but it doesn't drive itself. I could spend $1 million and it still wouldn't drive itself. Just because a machine is expensive doesn't mean responsibility for operation falls out of the window.

Several of us have given you a list of potential pitfalls in your solution, it's up to you to determine how to get around them. If you won't listen to those of us who have been there, done that, I don't see how much more help we can be. You're determined to make a fire prevention system that is likely doomed to not prevent fires, so I'll wash my hands of it now and just hope you don't get harmed in the process.

[Dan Hintz]

Maybe this helps
http://laserprona.com/new/wp-content..._SI-SG-SGX.pdf

Rodney, it's difficult to see, but it appears the sensor is the same type used for overhead sprinklers (alcohol-filled glass capsule)? I imagine if it's hot enough inside the cabinet to burst the capsule, the cabinet is already destroyed. The system may shut down the laser, but by then it's too late.

[Rodne Gold]

Dan , I have no idea of how it senses...
as you so rightly said , we as a community have given our input , so lets see what the OP can produce.
It might well work brilliantly and be $200... if so , I will take a dozen of em...

[Bill George]

On commercial HVAC systems they have smoke detectors in the ductwork. Sometimes one before the fan and one after. These could be set to sound an alarm, say 20 seconds before the CO2 goes off. It shuts down the fan and the fire suppression is triggered. CO2 is cheap and I would rather have it trigger and dump than not.
On laser systems the smoke detectors would need to be adjustable to a higher or lower level as needed.

[Dan Hintz]

On commercial HVAC systems they have smoke detectors in the ductwork. Sometimes one before the fan and one after. These could be set to sound an alarm, say 20 seconds before the CO2 goes off. It shuts down the fan and the fire suppression is triggered. CO2 is cheap and I would rather have it trigger and dump than not.
On laser systems the smoke detectors would need to be adjustable to a higher or lower level as needed.

Anything that can catch fire will create smoke in the laser, so the moment you start processing material the alarm will trigger... and no, you can't set a lower limit to the amount of smoke as there will often be LESS smoke once something catches fire.

In other threads, we've already discussed the danger to human life of dumping CO2 (or other gases) into the bed to smother the fire, so I won't rehash that here. And if you wait 20 seconds from the time the alarm goes off to when the gas is flooded, your machine is likely already melted.

[Bill George]

As a commercial HVAC tech who worked in many large computer rooms I saw systems that worked. If its good enough for a multi million dollar data center it should work for a $20k laser. The room is vacated (before) and ventilated after the dump.

If using a CO2 extinguisher is hazardous then are dry powder ones safer? Choosing not to put out a fire because of the hazards of using an extinguisher would be a tough choice.

There are many ways to detect a fire, UV detectors, flame flickering and temperature sensing that does not rely on melting a link or capsule. I have an Omron controller setting on my workbench that with a RTV or thermocouple sensor can pick up a temperature change in a manner of seconds.