Safety
Contents
- 1 Printer safety (FFF machines): Introduction
- 2 Handling risks
- 3 External safety
- 4 Operation
- 5 Risks
- 6 Safe printer design
- 6.1 Board/firmware design
- 6.2 External control
- 6.3 Electrical part
- 6.4 Fan failures
- 6.5 Fusing
- 6.6 Earthing
- 6.7 Wiring
- 6.8 Heater and thermistor fixation
- 6.9 Heater pad insulation
- 6.10 Limiting power on heating elements
- 6.11 Mains power switching
- 6.12 Relaying the power to stop heat generation
- 6.13 Use thermal cutoff
- 6.14 Electronic enclosure
- 6.15 Electronic cooling
- 6.16 Emergency Shutdown (ESD) button
- 6.17 Using the mains (110/230V) for bed heater or chamber heater
- 6.18 Enclosed machines
- 6.19 Fumes recycling
- 6.20 Smoke detection
- 6.21 Insurances.
- 7 Checking components
- 8 Accidents
- 9 See also
- 10 References
- 11 External links
Printer safety (FFF machines): Introduction
This page is about printer safety and how to handle it. Health and Safety is another page. There is also a page about Gaseous_pollutant_filtration.
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 injury 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 components 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. In case of faults, hotend heaters can reach temperatures capable to fuse aluminium (> 600°C), which are sufficient to start fires on most flammable materials.
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 components 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 may be too late to stop a fire involving a significant amount of high energy content products (the filament). Locating a sensor or an alarm near the printer will help early alarm, which is critical to limit or stop fire expansion.
- Manual extinguisher
- A manual extinguisher of sufficient size (4 to 6 kg) -dry powder ABC- shall always be readily available and functional. 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. Everyone in the home shall know where is the extinguisher and how to use it. Participate to training sessions. Check the manometer regularly and send to maintenance when required. If there is no manometer (for a permanent pressure extinguisher), buy a new extinguisher. You cannot check yourself a cartridge based extinguisher, so it is better to avoid them.
- 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 fuel, it shall be capable to stop an hydrocarbon fire. You shall choose an extinguisher of sufficient size (4 to 6 kg). The research key words are 'boiler automatic extinguisher' and they could be found for 50~100 euros. Here also an incorporated manometer is imperative.
- 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. Use a socket tester.
- Electrical safety breakers
- If not compulsory in your country, a 20mA resident current device (RCD) shall be installed on your electrical installation. In north America you can also find arc fault protection interrupters (AFCI) which are a quite efficient protection, unfortunately they are not available for domestic installations in others countries. When installing a printer, it is better to upgrade installation to latest regulation. Printers are machines (and legally considered as such in EU), not appliances.
- 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 shall access all compartments, including electronic and filament.
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.
Risks
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. see electronic cooling.
- 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 flammable parts. A common occurrence is the hotend heater falling down on print or bed.
- 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.
- Shorts or sparks on printed circuits.
- This occurs either because of poorly dimensioned tracks or by mechanical part shorting aside the fixation holes, notably for beds.
- 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. |
Heater failure | Intermittent contact may trouble the control loop. Cut circuit simply stop heat. More dangerous is internal short, as it will increase the power. In case of bed heater, that may lead to local overheating, not detected by the temperature sensor. |
Coherency between power input and temperature change rate | A frequent incident is the heating cartridge dislodged from the heat block. That will significantly modify the control loop answer and that shall be checked continuously, as a cartridge can ignite printed parts quite quickly. |
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. A lot of fan do have a rpm wire allowing rpm control as this is standard practice in computer industry. This shall be used to check that fans are properly operating. Unfortunately, very few boards incorporate this simple safety.
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.
Fusing
Printers with IEC plugs often include fuses on the mains input. This is not sufficient. Fuses shall be installed on the low voltage side. Different fuses shall be used for electronic and power. The best way is to have fuses on the board. Resettable fuses (often orange 'polyswitchs') have been prone to faults, unfortunately they are still in use in a lot of boards. They shall be replaced by real fuses. Automotive fuse type are compact and easy to find but not many boards are using them. Heaters driven by separated MOSFET boards or SSR shall have own fuses.
Earthing
For printers using only very low voltage (12~24V), metallic parts are not always earthed as such voltage is not considered dangerous for humans. However, earthing does not only protect humans, it also protect the machine by helping to trigger the fuses or the residual current device of your electrical installation. There is also the possibility that low voltage circuit enter in contact with the mains in the power supply which is a major source of failures. So earthing metallic structures of a printer shall be done whatever the voltage used for heaters. On DIY kits, the metallic enclosure of the power supply is often not covered by another enclosure. A frequent fault on power supplies is the absence of connection between the earth wire and the metallic case, which is particularly dangerous.
Wiring
Moving wires
When cables are connected to moving parts, it is important to use very flexible wires, and this is critical for heaters cables. Stranded cables are flexible but they are not all equal, some have a few strands (less than ten) and shall NOT be used for moving cables, as they will break after a certain amount of movement cycles, which can be dangerous if the break is close to the terminal as it induce heat in the near broken area. You shall use stranded cables with a lot of thin strands.
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 wires with silicon insulation used in RC models, which generally have more strands than ordinary wires. A sheath around the wires help maintain them and limit local stress.
Fixed wires
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.
Secured wire ends
Whatever the connection type, soldered, plugged or screwed, wires shall not apply any load on the connection because this will after some time drive to problems on the connection, either loose contacts or broken wires creating sparks. Partly broken wires also can overheat to very high temperatures. Problems occurs more quickly on moving wires, but this will also occur on power static wires due to vibrations. So all wires ends of moving wires and static power wires shall be secured just aside the connection, in order to release any load on connexion.
Crimped terminals on stranded wires
Stranded wires are flexible, so they moves and that creates fatigue at the connexion. To avoid breaks at connections on stranded wires, it is imperative to use crimped terminals. This is a regulatory requirement on all CE certified machines. Tin plated wire ends shall never be used as they creates a weak point at the end on the tinned part.
Appropriate wire section
The wire section shall be adapted to the maximum current. That depends of the wire length, temperature and core numbers but sufficient section is also required for neat connection to the terminals. For stranded wires, a large number of cores is preferable as it increase flexibility and so, resistance to fatigue, but it reduce the current capabilities. This is why below table have relatively low rating as it is for large core number wires. A large number of cores typically reduce the current rating by half compared to single core.
AWG [1] | Section (mm2) | Current (A) | |||||||||
24 | 0.2 | 1.4 | |||||||||
22 | 0.33 | 2.1 | |||||||||
20 | 0.52 | 3.5 | |||||||||
18 | 0.82 | 4.9 | |||||||||
16 | 1.31 | 7 | |||||||||
14 | 2.08 | 10 | |||||||||
12 | 3.31 | 14 | |||||||||
10 | 5.26 | 21 |
Section (mm2) | Current (A) | ||||||||||
0.5 | 3.5 | ||||||||||
0.75 | xx | ||||||||||
1 | xx | ||||||||||
1.5 | xx | ||||||||||
2.5 | x | ||||||||||
4 | xx | ||||||||||
6 | xx |
- | 25W | 30W | 40W | 50W | 80W | 100W | 150W | 200W | 300W | 400W | 500W |
---|---|---|---|---|---|---|---|---|---|---|---|
12V | 5.76Ω | 4.8Ω | 3.6Ω | 1.44Ω | 1.8Ω | 0.96Ω | 1.39Ω | 0.72Ω | 0.48Ω | 0.36Ω | 0.288Ω |
24V | 23.04Ω | 19.2Ω | 14.4Ω | 11.52Ω | 7.2Ω | 5.76Ω | 3.84Ω | 2.88Ω | 1.92Ω | 1.44Ω | 1.152Ω |
Checking wiring connections
Wrong connection occurs, often on the crimped part, so you shall check the component where doable after their assembly. There is no simple way to check board connections, but if there is intermediate connection on a wiring, like is frequently done on hotend, you shall check component through the wire harness:
- Unplug you hotend/heater, etc. from the board
- Measure the heaters, thermistors, fans through the complete wires at the board connector.
Accidents
See [Forum thread]. Owner had made an analysis and tests to reproduce the incident. Probable cause: Non-secured wire harness dislodged the heating cartridge which fall down on the print. Firmware had only a timeout on setpoint temperature but did not check the temperature change rate against the power and did not detected the fault. See board safety.
See also
- Board safety
- Electronic cooling
- Health and Safety
- Gaseous pollutant filtration
- Crimping
- Power supply
- Choosing a Power Supply for your RepRap
References
- ↑ https://www.engineeringtoolbox.com/wire-gauges-d_419.html
- ↑ Reprap forum: Power switch fail permanently conductive
- ↑ http://forums.reprap.org/file.php?392,file=24785,filename=Rex_C100.jpg burned independant controller
- ↑ https://www.kickstarter.com/projects/1064868871/smoke-signal-a-safety-system-for-3d-printers
External links
References
- Safety and best practice list on RepRap forum
- 3D printer Safety on Google Deltabot forum
- Fire safety on Google Deltabot forum
- Desktop 3d printer safety
Accidents
- Beware your 3d printer they can cause fires Burned house
- Yes, 3D printers can go on fire Fire caused by a short at night. Very lucky it does not extend.
- Fire hazard Printer catch fire
- Here's a reminder to not leave your printer unattended Entirely burned printer
- My 3d printer almost burned down my house today Fire due to a connector
- What happens when 3d printer catch fire Fire from a heating element falling from hotend
- burning down the house Board burned due to too small wire gauge
- House fire... Thanks to cheap printer from China... Entirely burned printer. Fire stopped by firemen (no one in house). Aluminium ladder above the printer was melted.
Tests
- Video of a thermal runaway test melt the aluminium block, fall down and burn
- Counterfeit/rebadged SSR
Technical papers
- Low voltage The incompetent ignition Source Electronic Ignition by contamination with low energy inputs
Safety equipment
- Fire proof enclosure and others suggestions Thread on reprap forum
- Fire proof enclosure Thread on soliforum
- Video: Automatic fire extinguisher demo
- Video: Use of manual fire extinguisher
Insurances
- State Insurance/IAG will not insure a house
- waiverdisclaimer advice for customer of a product Risk associated with the produced part
- 3d printing offers new risk challenges
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