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Printer safety (FFF machines): Introduction

A 3D printer using filament deposition is a complex machine involving electricity, parts in movement, hot temperature elements, flamable parts and high energy content consumables. It does present significant risks.

A lot of machines are open and if not, they could be opened in service, so there is some risk to have fingers pinched. However, motor strength is not large and the risk of serious is low, even for children. Being powered electrically, there is some risks associated with the power supply and associated wiring.

The power supply part is something quite standard, and it is dangerous only if cheap component are used, which is frequently the case. With temperature which may rise to 300°C in service and high energy content consumables (the filament), the biggest risk is fire and there has already been accidents.

The 3D printer world is not technically mature and there are no standards. In addition, a lot of people involved in machine development, notably in reprap world have very limited experience in safety handling, so the design often does not take into account basic safety rules. In addition, there are a lot of low cost equipment, particularly in electronic area, with chosen component known to fail in very dangerous manner.

300°C is often the maximum design temperature, but could be largely exceeded in case of failing component, driving to temperature above the ignition point of a lot of parts or consumables in the printer. Users have experienced incidents with temperature capable to melt aluminium.

Handling risks

There are three ways to handle risks, which shall be used simultaneously:

  • By machine design.
  • By installation of external safety components
  • By doing operation in a manner taking into account the risks

As for now, without safety standards and incitation to proper design, with low cost components and absence of real certification (even when compulsory as in EC), consumers 3D printer are dangerous equipment and shall be handled as such.

External safety

  • Fire alarm
    • A fire alarm is an imperative requirement, and it may be compulsory in some countries (EC). While the triggering of a fire alarm may save your life, it is generally too late to stop a fire involving a significant amount of high energy content products (the filament).
  • Manual extinguisher
    • A manual extinguisher of sufficient size (4 or 5 kg) -dry powder ABC- shall always be readily available. A printer fire is more difficult to stop than other kind of fire which may occur in domestic life and small extinguishers are not sufficient.
  • Fire blanket
    • A fire blanket may help stop a small fire without the mess created by a powder extinguisher, which is aggressive chemicals.
  • Automatic extinguisher
    • An active safety, say automatic extinguisher -dry powder ABC- is not very costly and could really improve safety. Such equipment designed for boilers is easy to find. Being designed for gas, it shall be capable to stop an hydrocarbon fire. You shall choose an extinguisher of sufficient size. The research key words are 'boiler automatic extinguisher' and they could be found for 50~100 euros.
  • External electrical power shutdown
    • Easily available electrical power shutdown. You shall be able to easily shut down the electricity, while the printer and equipment aside is burning, so relative location of the breakers and printers shall be carefully chosen.
  • Proper electrical earthing
    • Earth shall be connected to a valid earth, never on plumbing.
  • Electrical safety breakers
    • If not compulsory in your country, a 20mA safety breaker shall be installed
  • Easy evacuation
    • How could you escape if your printer and filament is burning ?
  • Fire containment box
    • This is a possibility, but is complex and make printer operation less easy. However, that may be the only solution yet to run a printer unattended, provided an automatic extinguisher is installed inside or outside the box. If inside, the extinguisher flow flow shall access all compartments, including electronic and filament.


  • No printer shall remain unattended
    • As printing is often a quite long process, people are really tempted to leave their printer unattended. With the state of the art, it is unreasonnable to leave printer unattended, especially while these printers are built with cheap electronic, known for frequent failures.
  • Safe location
    • Printer shall be located in a place where an eventual fire will have difficulties to propagate and where access is easy to combat a fire
  • No filament storage aside the printer
    • Filament are hydrocarbon and they burn quite similarly to liquid fuel, so they shall be installed in a place which will be the last to be reached by a fire. As soon as filament storage space is burning, fire became uncontrollable with simple extinguishers.
  • No flamable part aside the printer
    • Frequently printers are installed in DIY areas, with a lot of flamable stuff (wood, paint, solvents, etc.). That shall be avoided. Remember that drywall, brick or concrete are the best way to limit fire propagation.


What are the problems ?

  • Thermal runaway
    • There is in a printer at least one heating element with a control loop. If for any reason, which could be related to software or hardware, the heating cease to be controlled, the temperature could rise, sometimes relatively quickly to a value capable to start a fire
  • Hot parts cooling failure
    • Most printers requires permanent cooling while heating. Fan failures are frequent and may drive to excess temperature, which does not always start a fire, but may drive to destruction of supports, hot parts falling down to easily ignited area
  • Electronic cooling failure
    • There could also be electronic board cooling failure, which may drive to component failure, starting thermal runaways
  • Mechanical failure
    • In case of mechanical failure, due to uncontrolled movements or more frequently, hot part support failure, the hot parts may come in contact with flamable parts
  • Wiring failures
    • Movements of the printer creates a lot of stress on the wiring and connections and failures are frequents. That may drive to shorts or contact between wires and hot parts, causing harm to the control board, which may end badly. There is an example of someone who started a fire on its control board because of a short in stepper wires.
  • Electronic component exploding or bursting in flames. This could be due to components failures, shorts, underspecified or counterfeit components.
  • Power supply failure
    • PC power supplies are standardized and relatively safe. However, notably for voltage over 12V, power supplies often used in 3D printers are the one designed for LED supply and they are frequently very poorly designed and manufactured. Also, earthing is not always properly done.

Safe printer design

Board/firmware design

see Board safety

Thermal runaway
Causes Defense
Control loop software being freezed in heating A control of coherency between the measured temperature and the target shall be done
Whole firmware freezed, letting the heaters on Shall be controlled by a 'Watchdog' being it incorporated in the processor or being a physical watchdog on a processor pin
Control loop software perturbated by temperature measurement sensor failure Thermistor failure/disconnection shall be detected by the software, as they give off the range values
FET failure, locked conductive. Known to occur frequently on cheap RAMPS boards With designed as done on nearly all existing printer, such a failure could only be controlled by stopping the heating power (12/24V). If the power supply is an ATX PC power supply, the firmware could stop the 12V via an input on the power supply. For other kind of power supply, a relay is needed, but rarely present. This is one of the most common hardware design fault.

External control

An external control of overtemperature will help detect these failures, but need another processor and other temperature sensor. One user reported doing this external control with an external computer RaspBerry Pi, which run this task in addition to the printer and camera control. The computer being already existing on a lot of setups, the extra-cost is limited to temperature sensor and programming work.

On some printers, the LCD panel is handled by own processor. It could be used to do this external control.

Electrical part

  • Do no forget earthing
  • Power supply '-' shall be connected to earth
  • see power supply

Fan failures

Due to the very low quality of most fans installed on printers, fan failures are frequent.

If they are in charge of electronic cooling, that can drive to electronic failure.

If they are for hotend cooling, there will be a slow increase of temperature of the hotend which may end in complete destruction of the support and the fall of the hotend causing wire shorts or ignition of materials. Insulating hotend supports may help reduce this risk.


Moving wires

  • It does exist special cables for robots, capable to handle safely millions moves. For cost reasons, this may not be used in 3D printer, while printer movements are more demanding than on a robot, as it is faster.

You could find flexible cables with silicon insulation used in RC models, which is a better solution than ordinary wires. A sheath around the wires help maintain them and limit local stress.

For fixed cables, while there is no movement, it shall be taken into account that most printer vibrate, so the use of flexible stranded wires, as used in car or industry, is preferable.

For stranded wires, it is imperative to use crimped terminals.

Relaying the power to stop heat generation

As FET often fails in a conductive position driving to unstoppable heating, using relay to shut down power is recommended.

DC/DC SSR generate a lot of heat and need heat-sink. Mechanical relay cost lest and don't create heat but they are actuated by a coil needing more current than could be supplied by a processor output, hence it is required to use a transistor as first stage to command the coil. Board relays with opto-insulator for command are easy to find but the quality of their design and safety have been questioned.

It is good practice and could be required by some standards to use 2RT (2 contacts) relays and use both contacts in serie for a safer shutdown.

Electronic enclosure

To avoid the risk linked to electrinc component explosion or bursting, electronic could be installed in a fireproof enclosure. One possibility is to use an old power supply enclosure.

Electronic cooling

see dedicated page Electronic cooling

Emergency Shutdown (ESD) button.

An emergency shutdown button labeled as such shall kill all power and be directly wired on the main supply. Wiring an ESD button on something else than the mains is misleading and non compliant with most safety rules. In case of emergency, you may want to intervene with fire extinguisher, fire blanket, etc.

Such button is imperative if your printer does have heating on the mains (for bed heater or chamber heater). If there is only a general on/off button it shall be clearly visible and easily accessible.

External power blocks shall be installed on an accessible switchable plug.

Using the mains (110/230V) for bed heater or chamber heater

For large printers, the power needed by a bed can be significant and it does not look very clever to transform current just to make heat. So some people supply their heat bed and chamber heater in 110/230V. Earthing shall be properly done and due to risk of cable wear this is only acceptable for fixed bed (e.g. for deltas)

If the control loop is done by an independent controller, this could be an electrically safe solution. But that add another source of risk, the controller [1] However, it does have some advantages to have the bed and chamber controlled by main board, which needs a thermal sensor connected to the board. The weak point is the insulation of this sensor. For cost reasons, galvanic insulator are never installed on sensors, so an electrical insulating problem on the sensor may end having the mains voltage connected to the control board, which could be dangerous. A power supply act as an electrical insulator, a safety you loose with direct mains supply.

Enclosed machines

Machines could be enclosed to reduce the noise, add heat chamber or recycle fumes. A fire which developed in a confined space will stop while oxygen is depleted, so the design shall be as such as there is no input and exhaust of air. Indeed, for recycling fumes, machine shall be somewhat tight. Melaminated wood act as a fire retardant because melamine release Nitrogen while burning, however while burning melamine products toxic fumes. The electronic protection shall be handled separately.


There was one report of an insurance refusing to insure home if a 3D printer is used inside. With increase of use of 3D printers, this kind of insurance disclaimer may expand and you may check with your own insurance if you are covered for this use.

See also


External links




Technical papers

Safety equipment