<p>From what I've seen, you can take a typical extruder heater, apply the designated supply voltage without temperature control, and as long as the heater isn't contacting something with a flashpoint below the temperature the heater reaches, the heater will not catch on fire.  Thus, unless one catches the filament on fire, it seems that thermal runaway of the extruder heater wouldn't normally start a fire.</p>
<p>I'm not sure what would happen if someone installed wrong components, such as a 12V heater to a 24V supply. What are situations that could cause a 3D print to catch fire?</p>

[{'answer_id': 15304, 'author': 'FarO', 'author_id': 2338, 'author_profile': 'https://3dprinting.stackexchange.com/users/2338', 'pm_score': 2, 'selected': False, 'text': '<p>A normal hotend will not melt or cause fires, usually, see first video. However, if the power regulating unit fails as well and higher voltage is supplied (19 V on 12 V cartridge are enough) it can happen, see second video.</p>\n<p>Fires are more likely caused by overheating wires, especially where joints are presents.</p>\n<p>Hotend runaway does not cause fires from the hotend itself, but it could cause fire related to its wiring. Also, the uncontrolled temperature may make the hot end fan fail, worsening the situation.</p>\n<p>Issues canbe caused also by a runaway on the bed and overheating MOSFETs.</p>\n<p><div class="youtube-embed"><div>\r\n                <iframe width="640px" height="395px" src="https://www.youtube.com/embed/rPvKBRpU0bo?start=0"></iframe>\r\n            </div></div></p>\n<p><div class="youtube-embed"><div>\r\n                <iframe width="640px" height="395px" src="https://www.youtube.com/embed/qVjWg2vuWzk?start=0"></iframe>\r\n            </div></div></p>\n'}, {'answer_id': 15305, 'author': 'user77232', 'author_id': 12857, 'author_profile': 'https://3dprinting.stackexchange.com/users/12857', 'pm_score': 2, 'selected': False, 'text': "<p>In short:</p>\n<ul>\n<li>The control board does not have thermal runaway installed</li>\n<li>The heated bed connectors are loose and begin to heat up until the wires catch fire</li>\n<li>The power supply or it's connectors begin to heat up until they catch fire</li>\n<li>The modifications that you made to your printer were not well thought out resulting in a capacitor to explode (raises hand; that's happened to me.)</li>\n</ul>\n"}, {'answer_id': 15310, 'author': 'cmm', 'author_id': 2082, 'author_profile': 'https://3dprinting.stackexchange.com/users/2082', 'pm_score': 2, 'selected': False, 'text': "<p>Another source of fire comes from connections, not the heaters themselves.</p>\n<p>As the connection and connector ages, the electrical resistance of the connection increases.  Up to a point, this is not a problem.  A portion of the energy goes to heating the connection, and less energy goes to the heated element.  These are in closed loops, so energy is applied longer to compensate.</p>\n<p>The connection is using the lost energy to heat itself.  This increases the corrosion rate, and also can cause plastic in the connector to flow, which relaxes the connection pressure, which further increases the corrodion, resistance, and heating.</p>\n<p>This situation is unstable, and ends in one of three ways:</p>\n<ol>\n<li>the extrusion hot-end or the bed don't get as hot, with implication on the print quality,</li>\n<li>the connection opens, and the heated system simply fails,</li>\n<li>or the worst case, where the temperature increases to the point where the connector housing, wire, heater PCB, or dust and fur on the connector catches fire.</li>\n</ol>\n<p>The only real mitigation of this risk is to periodically check power connections for warming.  If a connection is warm, it should be watched more carefully.  If it is hot, you already have a problem and should fix it.</p>\n<p>If you are concerned, focus on preventative maintenance, and on being sure that there are no flammable materials near the printer.  Don't put your printer in a simple foam case.  Consider the flammability of any enclosure components.</p>\n<p>You might also consider adding a smoke and high-temperature detector connected through a relay to disconnect main power.  If a connection starts sputtering, you might detect it before the fire can transfer to your house.</p>\n"}]
['https://3dprinting.stackexchange.com/questions/15303', 'https://3dprinting.stackexchange.com', 'https://3dprinting.stackexchange.com/users/15075/']