Introduction: Is 3D Printing Safe? or DIY Testing for HCN From ABS and Nylon 3D Print Material
And, what exactly is "safe" anyway..?
If we eliminate the obvious, the fact that the belts and motors can pinch a finger as well as a heater block operating at 200+c will definitely burn you, we are left with the one unknown. That is of any hazardous fumes and odors that may be emitted by heating the plastics. We not only can't see these gasses, but most of us don't have a device at hand to make a measurement.
The intent of this DIY is to explain how to build a test apparatus to determine the safety of the material you are using to print your parts. Of course in doing so, we were able to measure and report on various common matereials.
If you just want an answer to the question "Is 3D Printing Safe" without reading the excruciating details, you're in luck.
"Yes" Based on our measurements using the world Safety Authorities (OSHA NIOSH ACGIH) Limits, 3D Printing is safe.
There was NO measured HCN from "3D Printing ABS" based materials at specified temperatures.
There was NO measured HCN from "3D Printing Nylon" based material at specified temperatures.
There was 0.1ppm of HCN while printing with a "Non-3D Printing" material (Trimmer Line)
Even in our worst case testing in an enclosed 12" cube at 420C (788F) for 10 min the maximum reading was 1ppm, again, trimmer line. The OSHA safe limit is 4.7ppm.
Quick Q and A
Did you find any items of note?
- We found that before the threshold was reached, the plastics became "unprintable" and would halt/jam the printer.
- There is a lot of naturally occurring HCN. You will probably encounter more HCN at an outdoor marshmallow campfire than we measured in our testing. Due to it's shear quantity as opposed to the small quantity we print, burning wood creates a lot of HCN.
- Again, our testing shows no HCN measured from 3D Printing materials at correct temperatures.
What gas would make 3D Printing unsafe?
An excessive amount of Hydrogen Cyanide (HCN) - A gas emitted by plastics when they are set on fire or breach pyrolysis.
And what is an excessive amount of HCN?
The international (OSHA NIOSH ACGIH) maximum allowable exposure to HCN is 4.7ppm
So? How much HCN did you measure while actually printing?
3D Printing ABS from various 3D Printing material suppliers in China, the EU and US = None
3D Printing Nylon from taulman3D 3D Printing material supplier in the US = None
Two brands of Trimmer or weed-whacker Line mfg in the US = .1ppm
Where did you get the 3D Printing material?
Defined 3D Printing Material -
ABS1 = China - A
ABS2 = China - B
ABS3 = EU
ABS4 = US
Nylon1 = US
Nylon2 = US
Non 3D Printing Material -
Trimmer1 = US
Trimmer2 = US
What did you use to measure the HCN?
Industrial Scientific Corporation T-82 Single Gas Monitor
Calibrated HCN Sensor
Certified calibration 1 day before testing
Certificate of calibration
Certified by UL, CSA, CE
What was your absolute highest reading?
Trimmer line "A" at 220c+ = 0.6ppm -1.0ppm in a semi-sealed enclosure (12" x 12" x 24") for 10 min
This is a "cumulative test" as the gas is allowed to accumulate in the enclosure, thus it's concentration in ppm is higher.
This is NOT a printing test, but one of several tests done to answer cumulative concentration questions.
Today, most 3D Printers use modular power supplies. Either re-purposed ATX (Computer PS) or enclosed wall power units, such as used by laptop computers. These are already UL listed and tested. Most of these power supplies don't exceed 24 volts, including power to the Hot-End.
Again, there are obvious safety concerns with respect to motors and belts, pulleys and or threaded rods. However, once we see these components in operation, we know to use a bit of caution and not stick our fingers in the moving parts.
There are a few hot components we need to be aware of.
- Stepper motors - These can get hot, but usually not hot enough to burn you. Most motors have an attached fan to keep them cool so as to last longer as heat damages the motors bearing surface over time.
- Power supply - These are covered units, but as they dissipate heat we need to make sure they have access to ventilation, i.e. don't block the little cooling holes and replace air filters when needed.
- Build table - These are the platform we actually print onto. They are usually heated to a temperature that will burn you. Almost all of these are vividly marked in some manner warning of "HOT" and "Do Not Touch". This is an actual UL requirement if the printer is certified.
- Hot-End or Heater block - This is the component where the plastic is melted and flows from a small opening/nozzle. This will be very hot. Between 180C (356F) and 275C (527F). Again, this will not just burn you, but mark you for life. Recently, you may have noticed that some 3D Printers have started to ship with brackets, or shields around the Hot-Ends. And in some cases, a completely enclosed printer where access is only through a door or lid. This comes from various UL and CSA requirements for finished goods where rules to protect the consumer come in to play. As of yet, 3D Printer kits have not been required to meet a lot of the same rules.
While most of us have tape measures and wrenches to make mechanical measurements/adjustments, volt meters to make electrical readings and temperature sensors to measure hot parts, almost none of us have unique gas detection equipment to detect gasses emitted by printing. And because we are changing the state (heating and melting) of plastics, they will emit fumes and odors.
3D Printing Measurement History
We can't say that no one has made this specific measurement prior to now, just that we were not able to find any information on-line or through contacts.
Step 1: Safety
First, research the history of similar conditions or testing.
Research was extremely easy. A simple Google search on HCN measurement techniques along with some outreach to injection molding companies proved that this has indeed been tested and certified safe in much larger quantities.
3D Printing is really just die-less injection molding. The plastic is heated and forced to go where we desire. It cools and we have a part. So, the injection molding specialist are a good place to start. Contacting a major injection molding company in the eastern US, we were able to get the Industry Standard on injection molding safety and hard measurement of HCN with Nylon specifically. For Nylon, the industry goes by what is known as "The Barns report". This is a full up actual real time HCN testing of a injection molding machine running at 270C with 100's of pounds of material. The resulting HCN measurement was less than 1ppm, so we assumed with a tiny amount of Nylon, we were pretty safe. However, we were also going to do some "cumulative testing" where we all but seal up a specimen and heat it to extremes of 400C. More on that later.
So we're about to build a tester to test for hazardous gasses. And in doing so, we will intentionally create a worse case 3D Printer condition to force the generation of these gasses. What precautions should we take?
- No Bystanders - This is not something you do while a bunch of folks are in the next room eating lunch. Alert everyone in the building you're going to generate hazardous gasses.
- Dead Man switch - Well, not really, but you need to be able to turn heater temperature "OFF" outside of the danger area.
- Remote Visual - If while performing the test, you reach the OSHA Limit, you are to immediately leave the room to seek clean air. To understand if you can return, you can use a WIFI connected video camera pointed at the sensor.
- Ability to vent the room remotely. - If extremes happen, and someone does not get to leave from collapse or they have been overcome, you must be able to quickly vent the room to allow safety personnel access.
- Clean up - At low temperatures(78F) , HCN gas can liquefy on surfaces. After each test, you must wash off/spray off any surfaces that will be used for the next test as HCN can linger. In addition, you must wear typical nitrile gloves to keep from absorbing HCN through contact that has accumulated on cool surfaces.
- Have a smoke detector as you never know.
- Location was a garage with no other inhabitants.
- The Heater cartridge was on an extension cord that looped 100' from the garage.
- We had a WIFI enabled video camera on the test setup including the HCN sensor.
- We had a 130 cfm vent in the top of the garage and the power garage door remote.
- We used a power sprayer for clean up and just sprayed water. No other chemicals.
- We had a smoke detector and fire extinguisher.
If for whatever reason you suspect that your sensor may not be calibrated or working correctly, there are two additional early warning alarms you can use.
Bugs, yep bugs. HCN is considered a great bug killer as bug's will literally drop out of flight if they encounter anything above about 1.8ppm of HCN.
- The odor of almonds. This is in the literature and sounded a bit odd, but we are now believers as we got a whiff while testing trimmer line at elevated temperatures. We were reading spikes at about 0.6 - 1.0ppm when we detected this odor.
This testing may be performed by experienced, skilled users, at their own risk. to the fullest extent permissible by the applicable law. taulman and taulman3D hereby disclaim any and all responsibility, risk, liability and damages arising out of death or personal injury resulting from any testing defined or described.
NOTICE: HCN is considered lethal at >30ppm
This testing was performed by the taulman3D group. taulman3D.com is now a vendor of new Nylon based 3D Printing materials.
Step 2: Column Assembly for Measuring Gasses From 3D Printing Materials
Measuring gasses with the correct equipment is very simple. We set up a column or tube for the gasses to pass thru undisturbed by surrounding forces such as fans and wind. We allow for air to be pulled in by thermals created by the hot end. We then create an opening or escape equal to the physical proportion of the heating element and at that opening, we place our measuring sensor. As the temperature increases, the air heats, warm air rises and gasses lighter than air are carried along the path. The mixture of hot air and gasses passes by the sensor element creating a change in the sensor that corresponds to an increase or decrease in the displayed reading. Scientist write entire books on this process, but at the end of the day it's......Hot air, gasses, sensor and a reading.
The column we used is a simple 2 cubic foot acrylic assembly. 4 each pieces of clear acrylic and one each 12" square piece of plastic to serve as a lid. Clear acrylic was selected as we would video capture the degradation of the material at the same time temperature was increasing. This way we could spot the affects of degradation and correlate to some degree the amount of gasses detected.
The lid is cut at 5" in at the corner. This allows us to make a slot for the exhausting air and gas mixture. The 4 panels are glued or taped at the seams to minimize leakage. We selected glue as we were going to use a power washer to clean the column after each test. We also strapped large wire ties about the unit to help maintain stability.
Each bottom corner has a one inch plastic standoff or mounting foot to raise the column off the table about an inch along the bottom. This allows air to be drawn in as thermals start under increasing temperature.
- 4 each 12 x 24" acrylic panels 1/4" thk
- 1 each 12" square plastic for the top
- 4 each spacers of mounting feet
- Glue for the seams
- Support Straps - We used 14" long ties
Step 3: Heater Block Assembly
The other end of the 3/16 rods are mounted in a piece of steel or aluminum to balance the heater block and hold it upright during testing. Make sure it's steady as you don't want it falling against the acrylic at 300C..!
The thermocouple twisted wire connects under the nut next to the heater cartridge. This will measure our sample temperature.
To adjust temperature we use a variac. This allows us to dial in any voltage needed to acquire a desired temperature from the heater cartridge. A word on variacs.....they are NOT isolated, so always turn them off before touching the cartridge leads.
- 2 each 3/16 x 12" threaded rod
- 4 each 3/16 nuts
- 1 each thermocouple "K"
- 1 each Heater cartridge McMaster Carr 120 volt 80 watt
- 1 each variac or power source for the heater cartridge
Step 4: HCN Sensor
We will need an HCN sensor that is calibrated within the last 30 days using a known calibration source. In the case of HCN, the best calibration is done by a certified agency with a canister of registered HCN gas. We selected the Industrial Scientific T-82 sensor as it is a higher resolution sensor (0.1ppm) as well as a leading brand used by firefighters as well as industry and chemical engineers worldwide. We requested certified calibration documentation along with quick instruction as to capabilities. The unit is more expensive than most single gas detectors but has a better rating than most.
Smoke and CO
Any standard smoke and CO detector as these are highly UL regulated and there are constant factory calibrations checks.
Step 5: Equipment Setup for Dynamic Testing
- Heater Block Temperature - This is what will heat our plastic samples
- Exhaust Temperature - This is just to show that the temperature is increasing as a thermal affect of air flow past the heater block.
- Heater Cartridge AC Voltage - This is used to adjust the voltage up in steps - 50, 60, 70, 75, 80, 85, 90, 95 and 100 volts AC
- Smoke and Carbon Monixide Detector
- HCN measurement of emissions
- 1 each Column
- 1 each variac
- 1 each clock = any
- 1 each Smoke Detector = Any Combination Smoke and Carbon Monoxide Alarm
- 1 each Digital Voltmeter = Cen-Tech 90899
- 2 each Digital Voltmeter = Cen-Tech P37772 w/K Thermocouple
- 1 each HCN Sensor = Industrial Scientific T-82 or equivalant
- 1 each test sample
Step 6: Equipment Setup for Confined Testing - Not Required
Confined testing was done to capture total HCN from a sample.
In this case, the lid is sealed and no gasses are allowed to escape. The result is to capture the "total" HCN emitted for a sample, undiluted by the surrounding air. The HCN sensor is placed inside of the column and as it is clear, values can be seen.
The following are measured per the photo:
Heater Block Temperature - This is what will heat our plastic samples
HCN measurement of emissions
NOTE: This is not a part of the required 3D Printing test and is added here as a point of interest only.
There were over 20 hours of video and several hundred readings taken by taulman3D for the materials noted and several materials not mentioned here.
Step 7: Equipment Setup for 3D Printing Test
In this case, a 2BEIGH3 3D Printer was moved to the garage and used for measurements during actual 3D Printing. In short, the 2BEIGH3 is a large 3D Printer capable of printing several types of materials. You can learn more about the 2BEIGH3 here.
In this case, a large plastic container was used as a temporary hood to collect gasses rising during the print. There is a 1.5" dia hole in the top for gasses to escape, and as they do they pass directly across the path of the sensor module.
The unit was prepared to print a part known as a "Material Certification Object". This is a part that is used to determine the quality of Nylon based printing material. It takes about 20 min to print a complete part.
Step 8: Testing Methods and Sample Materials
3D Printing Active.
This is simply a measurement of the collected gasses at the top of the 3D Printer during an actual print. The part printed is the "Material Certification Object".
Dynamic Error Testing:
This is the test where we determine the "what could possibly go wrong" and duplicate the issue in a controlled area - the column.
The assumption for this test, is a run-away heater resistor or cartridge. Any error that allows the heater block to increase temperature of the material while printing continues.
Gasses are emitted whenever pyrolysis is breached for all materials. Therefore we conducted some intermediate tests to determine the temperature that indicated a breach. When the breach temperature was determined, we moved to the 3D Printer and started to print at 20 degrees below this temperature with the intent of increasing temperature to the point of breach to discover any issues.
We discovered that in most cases contact of the plastics to the overheated nozzle resulted in a boiling type action that repels (adds back pressure) the material. As printing continued (1-3 minutes) , we eventually reached a point where the extruder pressure required was greater than the grip capabilities of the extruder and material slippage ensued. Within a minute, the material was cut through by the extruder teeth and pressure ceased.
At this point we realized we would need to start at a lower temperature and again increase till we meet the pyrolysis value. We then discovered that while we could print slightly longer, as the nozzle approached a pre-breach temperature value, the same effect began and extrusion stopped. The purpose was to determine the amount of material still in the hot-end that could now continue to be exposed to an ever increasing temperature. The amount of material for 2 tests was almost identical at .3grams or about 24mm of 3mm ABS material.
We now have an "amount" of material for our Dynamic testing.
As we were testing 3mm, 2.8mm, 2.1mm and 2.9mm material, testing samples were cut by weight rather than length.
Combined or Cumulative Testing:
The next set of tests were to measure the accumulation of gasses in a small enclosed space. HCN is lighter than air and will accumulate at the highest spot in the room. As it transitions into the room, it is diluted by the total volume of air in the room. Thus, while a reading directly above the exhaust slot may be 1ppm, by the time that small volume dissipates within the room, it is almost zero. As the opening or slot in the the lid during dynamic testing was about 3 square inches, it represented a column of combined gas and air of that same size. Therefore it can be said that a reading of 1ppm was a reading within a 3 inch rectangular column. That column of mixture expands to about 4 feet square as it rises to the ceiling, and therefore, the PPM declines in kind.
The goal of this test is to determine the absolute worst case accumulated HCN emitted by two each failed 3D Printers operating in an small space. The amount of sample material was doubled to equate to two failed units. The results could also be useful for those with printer farms as they typically use 8+ printers in close proximity.
All 3D Printing ABS materials tested are available on-line from a long list of respected vendors here.
NOTE: There was almost no variation in test results from one ABS vendor to the next.
All 3D Printing Nylon materials are available here,.
All non-3D Printing Trimmer and Weed-whacker Line are available at most Home Improvement stores.
Step 9: Test Procedures
Dynamic Error Testing:
If you are using material listed here, then you can skip the Dynamic testing and move to the 3D Printing Active testing.
If you are testing a completely new and a "known to be untested" material, then we suggest you start with the Dynamic Error testing as more safety is involved.
Setup your test equipment and column as shown in step 5
Open a 1" wide exhaust slot on the plastic lid of the column.
Make sure the sensor element is in the line of hot air flow.
Remember to read the safety Step 2
If you don't have a scale for the material, 3mm ABS is about 24mm 3mm Nylon is about 27-28mm for .3 grams.
The intent is to measure any emissions at and slightly above the temperature you are going to use during printing. We suggest printing temperature plus 30 more degrees "C". This insures you are not on the edge of breaching pyrolysis. In our testing we went way beyond breaching pyrolysis for other evaluations. The system defined here uses a variac to adjust the AC voltage to the heater cartridge. This is an open loop, but still maintained temperature within a few degrees. You can use any temperature control you need to slowly apply the heater voltage. The voltage rise along with temperature is meant to be slow, taking place over about a 30 min span. You can raise the temperature to about 125C quickly, but from there on, take it slow. With our setup we adjusted to 50 volts and allowed the temperature to rise to about 125-130C for a 120 volt Heater Cartridge. From there we stepped voltage up as follows:
60, 70, 75, 80 if needed.
Again, this transition should take about 30 min.
When you reach 30 degrees "below rated temperature, you should start logging every minute any HCN readings including "0" as you transition on up to rated plus 30.
Once at the rated plus 30 mark, let the material set at that temperature for 5 min, again logging HCN readings each minute.
At the end of the 5 minutes, the test is complete. You should average your readings.
Items of note:
1. If your peek reading is less than 4.7ppm, it is considered safe by OSHA and other health organizations. However, from our measurements, a value higher than 0.1ppm on average is unusual.
2. If the smoke detector sounded it's alarm, then the material is definitely unstable. The only material that tripped our smoke detector was trimmer line #2.
3. If the material spits out small puffs of smoke, then it is close to breaching pyrolysis.
4. HCN can "accumulate" at the ceiling of the room. Therefore a constant reading of 4.0ppm to 4.7ppm will accumulate to a higher value at the highest point in the room and this is why we want to watch out for unusual readings.
3D Printing Active
This is a basic monitoring of HCN sensor levels during the middle of a 3D Print. Again, we used the "Material Certification Object".
The printer is configured as shown with the large plastic hood or, in this case an inverted storage box. A hole about 2X the diameter of the sensor is cut on the hood for gasses to escape. The sensor detector module is placed such that gasses escaping will pass by the sensor. All cooling fans are to be turned off.
NOTE: The 2BEIGH3 uses NEMA 23 steppers and temp of these units reached 80C-104C with fans OFF. One unit required a replacement due to the number of tests. You should cool steppers between tests.
You will need to ensure that no room air currents modify the path of the rising heated air.
The printing temperature should be the maximum for most prints. This will vary from printer to printer and in some cases, the material may come with suggested temperature values.
If you use the "Material Certification Object", it has a wide and thin (4 - 8 layer) seat. Temperature should be settled by the time the center square begins printing. This will be the beginning of your measurements for HCN as read from the HCN sensor unit.
Document any readings including "0" every 30 seconds. Watch to make sure no reading exceeds 1ppm. After about 10 minutes of printing, you should have accumulated about 20 readings. This of course is the test of interest to most of us that print.
You should run an "average" of the 20 or so numbers to come up with an average value of HCN emissions. If your peek reading is less than 4.7ppm, it is considered safe by OSHA and other health organizations. However, from all of our measurements, a value higher than 0.1ppm on average is unusual. As mentioned above, HCN can "accumulate" at the ceiling of the room. Therefore a constant reading of 4.0ppm to 4.7ppm will accumulate to a higher value at the highest point in the room and this is why we want to watch out for unusual readings.
Step 10: Conclusions
First, we hope that anyone with concerns about the safety of their unknown 3D Printing material can use this DIY as a guide to eliminate guesswork.
Second, we were pleased with all of the test results as they prove that materials that we have all been using for years are indeed safe.
Again, when 3D Printing, you should always vent all fumes and odors.
A special "Thanks" goes out to:
Mike M. Physicist
Ken L. Engineer
Kristin D. Column Design
Jeff M. China Support