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Heated chambers, especially homebrew ones, might pose a fire risk if the printer inside has a really bad day and its TRP is defective or - oh horror - deactivated. We are dealing with a class A fire if it ever starts to smolder, so water is out. Many other firefighting measures - like an ABC extinguisher might destroy the printer. On a ferry, I saw signs that they had Halon firefighting in the machine room. But that stuff is near unavailable, the more fancy replacements expensive and a typical, pre made deployment system costs thousands.

Is there a way how one might set up a firefighting solution oneselves, using somewhat readily available parts?

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  • $\begingroup$ Crazy idea: operating the printer submerged in inert liquid. $\endgroup$ Jan 12 at 20:55
  • $\begingroup$ a $5 usb water pump can pump vinegar into baking soda, which produces CO2. $\endgroup$
    – dandavis
    Jan 14 at 19:05
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Firefighting Agent

One Halon alternative is the rather simple and cheap gas CO2. It is neither toxic nor hard to get: "60 liter" water-carbonation bottles are readily available over the counter to create soda water and contain some 200-300 liters CO2

Alternatives are Argon and Nitrogen, but those don't come in these small canisters and dissipate more quickly, but they also need the chamber to be gas-sealed.

Because non-flammable gases act by smothering the flames, it is vital that rooms in which such a gas firefighting system is installed are not rooms in which people are usually, and in case of a workshop, it might be required to disarm the automatic trigger while the door is opened!

Deployment System

Such a soda water machine also would deliver the most crucial parts of a deployment system: the valve. To activate it, a solenoid can be used - once current flows through the solenoid, the valve is pushed open and the CO2 will shoot out into tubing or piping leading into the build chamber.

The gas canister should under no circumstances be inside the build chamber's heated compartment but somewhat close.

Release System

Now we need a way to trigger the solenoid. I propose to use at least some redundancy in construction.

  • Manual Mechanical Override. This can be as simple as a lever that bypasses the solenoid and activates the valve manually. Also useful for functionality tests.
  • Manual Electric Override. Using a 9V block battery and some sort of latching switch/button. The solenoid is directly powered from the "reserve" battery now.
  • Automatic via a microcontroller. Using a small programmable chip, one could use a spare thermosensor inside the chamber to detect temperatures of dangerous levels. As a direct response, it triggers the solenoid to release the gas into the chamber and continue to do so for at least long enough to fully flush the chamber, even as the temperature drops with the injected firefighting agent. It might be best to also trigger an alarm, for example, a repurposed doorbell. If one goes for such a solution, an output of the current chamber temperature could also be integrated, though I strongly discourage from integrating the fire suppression as a part of the printer board!
  • Automatic via a thermal switch. More simple in design, a Normally Open Thermostat Switch could be used instead of a whole microcontroller. Such a switch could use the same power source as a manual electric override switch, and indeed, be mounted parallel to the same switch. The downside of a hard-wired thermostat switch is, that it sets a hardwired maximum chamber temperature. It'd be best to choose a switch with a reset-temperature that is as far from the trigger temperature as possible to ensure that the chamber contains as little O2 as possible. The availability of switch types here dictates the voltage of the system.

What about the chamber heat control?

Once the firefighting system engages, the chamber should no longer get access to fresh air. This could possibly be made by having a different solenoid push a shutter in front of the air intakes and/or by de-powering any chamber cooling fans.

Door Safety

A magnetic switch in the door should cut power to the solenoid, ensuring that only the mechanical manual override can fire the system.

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    $\begingroup$ @R..GitHubSTOPHELPINGICE because those are crazy expensive, one-use items, require water pressure behind them and are not available - unlike thermostat switches, thermosensors or... a stick of wax for the most simple version of a thermostat switch. $\endgroup$
    – Trish
    Jan 12 at 16:45
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    $\begingroup$ @R..GitHubSTOPHELPINGICE another benefit of the electric is, it shuts down after the temperature dropped enough, unlike a one-use glass vial. 60 liters of air could displace the whole air in a room - shutting the valve automatically is a safety thing in this case. CO2 comes at a benefit here: it is so much heavier than air, that it keeps a breathable atmosphere above it. $\endgroup$
    – Trish
    Jan 12 at 19:15
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    $\begingroup$ The commonly available CO2 bottles actually contain ~230 L of room-temperature CO2. The "60 liters" refers to the amount of water you can carbonate with one bottle. $\endgroup$ Jan 12 at 20:15
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    $\begingroup$ Is there any risk of the system freezing shut with solid CO2? $\endgroup$ Jan 12 at 20:17
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    $\begingroup$ You probably want a motion sensor in the room to help prevent locking someone in the room to suffocate. Ideally you want one that distinguishes people motion from hardware. $\endgroup$
    – Perry Webb
    Jan 12 at 20:28

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