Safety
Contents
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 fo 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. - 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, procided an automatic extinguisher is installed in the box.
Operation
- 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.
Printer design
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. - 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
| 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
Flamable part
Wiring
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.
See also
References
External links
Yes, 3D printers can go on fire Fire caused by a short at night. Very lucky it does not extend.
beware your 3d printer they can cause fires Burned house
