Are You Burning Plastic or Are You Welding Plastic?

This blog post considers differences: the differences between MSDSs, the differences between information in MSDS sections, and the differences between welding plastic and burning plastic.

Depending upon your answer to the question in the title, safety organizations have differing advice for you.

If you are burning plastic in a trash fire in your backyard, an environmental agency may tell you to stop because the temperature of your trash fire is not hot enough to destruct the chemicals created when plastic burns, chemicals dangerous enough to cause respiratory disease and cancer.1 A temperature of 1800°F, in a double-chambered incinerator equipped with air scrubber technology, is recommended to negate the toxic impact on the air.2

If you are heat-welding [also called hot air and hot gas welding] a plastic – perhaps using a rod with a designed-in temperature range well under 1800°F – should you be concerned about the air you breathe as you work?

Let’s consult the hazard identification and personal protection sections of the MSDS [material safety data sheet] for the plastic involved.

Thermal decomposition

In both situations, we’re really talking about thermal decomposition: the breakdown, due to heat, of polymers [plastics].

Depending upon the temperature, the plastic’s behavior may range from disorganization of its basic building blocks [the polymer chains of a thermoset plastic] to transformation into gases, fatty acids, and the original substances used to manufacture it [thermolplastic].3

For the purposes of exploration, this blog post focuses on one polymer, polypropylene [CAS Registry Number 9003-07-0], and what three polypropylene [PP] MSDSs say about polypropylene’s relationship to temperature, fumes and ventilation.

Categories of information on an MSDS

Manufacturers produce an MSDS to meet OSHA regulation 1920:1200 Toxic and Hazardous Substances with the intent of communicating information concerning hazards and appropriate protective measures to employees and to users of their product.
While all polypropylenes may have an associated MSDS, not all polypropylene MSDSs are created equal. The three under our review each have 16 sections, but the information in each section varies widely.

Welding rods for polypropylene

Because the welding of plastic occurs in many workplaces, we examined three PP MSDSs to see what they said about temperature, thermal breakdown, fumes and ventilation. The information we found, as displayed in the table below, is inconsistent regarding respiratory hazards. Only one of the reviewed MSDSs mentions personal protective equipment as a control to limit exposure to fumes created by high temperatures. 

Please note that the operative temperature range of commercial plastic welding rods for low-density PP is 82-163°C/180-325°F and for high-density PP the range is 325-345°C/550-625°F.

Compare those temperatures to the decomposition temperatures noted in the MSDSs. Note, for example, that MSDS 1 says that thermal decomposition may begin at temperatures above 300°C/572°F and that the result may include “methane and propane, carbon monoxide, carbon dioxide, aldehyde and other organic vapor.” Human lungs are not designed to breathe these substances.

Firefighting and polymers

We also reviewed a health hazard manual for firefighters3 for information about the impact of thermal decomposition of PP on the human respiratory system.
A summary of that information follows the table.
MSDS 1
MSDS 2
MSDS 3
Melting Temperature
163-174°C/325-345°F
260°C/50O°F
120-170°C/248-338°F
Flashpoint
300°C/572°F
440°C/824°F
200°C/392°F
Temperature-related Hazards
Irritating fumes may be produced at process temperatures.
Irritating vapors to respiratory system and eyes may form when polymer is processed at high temperatures.
Fume Remarks
Toxic gases will form upon combustion.
Irritating fumes may be produced at process temperatures.
Ventilation Remarks
Avoid breathing dust and processing fumes.
[No ventilation recommendation.]
Appropriate natural ventilation.
If user operations generate dust, fumes or mist, use ventilation to keep exposure to airborne contaminants below the exposure limit.
Ventilation is normally required when handling this product at high temperatures. Wear appropriate respirator when ventilation is inadequate.
Decomposition Temperature
Temperatures over 300°C/ 572°F may cause resin degradation.
Thermal decomposition products may include simple hydrocarbons such as methane and propane, carbon monoxide, carbon dioxide, aldehyde and other organic vapor. Carbon monoxide is highly toxic if inhaled; carbon dioxide in sufficient concentrations can act as an asphyxiate. Acute overexposure to the decomposition products may result in headache, nausea, and irritation of the eyes, kin and respiratory tract.
>300°C/572°F
Avoid temperatures above 300°C/572°F. Hazardous decomposition products are carbon monoxide, carbon dioxide, dense smoke and various hydrocarbons.
Inhalation Remarks
Vapors and/or aerosols, which may be formed at elevated temperatures, may be irritating to eyes and respiratory tract.
Inhalation of process fumes and vapors may cause soreness in the nose and throat and coughing.
Avoid breathing dust and processing fumes.
Dust may irritate the respiratory system.
The inhalation of high concentrations of dust may irritate the upper respiratory tract and damage lungs by accumulation.
Immediately take the person out into fresh air. If any irritation to the respiratory tract persists, seek medical care.
Irritating vapors to respiratory system and eyes may form when polymer is processed at high temperatures.
Fire Hazard
Use approved self-contained breathing equipment apparatus and other protective equipment if conditions warrant.
Personal fire-fighting equipment: No special equipment is required.
Fire may produce irritating gases and dense smoke.


Firefighters and plastics

Firefighters are encountering fires with more combustible plastics. The author of Health Hazards Manual for Firefighterssays “Practically every building today contains plastics capable of producing, upon burning, gases which can damage the lungs.”
The manual says that thermal decomposition of PP can produce volatile fatty acids, formaldehyde and acrolein [pages 4, 5], especially at temperatures of 300°C/572°F to 450°C/842°F – a range that includes the operative temperatures of welding rods for PP.
The manual says that high concentrations or prolonged exposure can constrict one’s breathing, may also affect the liver, and that formaldehyde is carcinogenic [page 9].

Not much of a difference

We looked at one common polymer, 3 MSDSs, and a firefighting manual to better understand the respiratory hazards associated with the thermal breakdown of plastics. The MSDSs alone are inconsistent when it comes to hazard identification and engineering controls – if they are mentioned at all.
We also reviewed two manuals4,5 on plastic welding for the auto industry; one of the two mentioned fairly standard safety equipment, fume extractors and respirators.

It seems to us that the difference between welding plastic and burning plastic is a small one when it comes to respiratory safety.

If you are planning to do plastic welding

  • We recommend you use the MSDS as a starting point. Make sure you read its information on firefighting, because you may find safety information that is unavailable in other sections.
  • Understand that a polymer may have additives and you may want to know what they are before you heat them.
  • Check around to see if anyone else is welding that same polymer. How are they handling respiratory safety? Their techniques may be appropriate for you, too.
  • Consider asking an industrial hygienist to sample the air before and after you weld so that you can design appropriate engineering controls.
  • If you smoke, you may be especially vulnerable to any fumes. A stringent local ventilation strategy may be particularly valuable.

Conclusion

At Sentry Air, we think the safety information regarding plastic fumes, smoke and temperature is inconsistent and could be made more useful if it incorporated polymer research done on behalf of firefighters.  
We also think all workers deserve to breathe clean air. We design and manufacture fume extractors for a wide range of industries. If you would like information on fume extraction options for your plastic welding process, give us a call at 1.800.799.4609, email us at sales@sentryair.com, or fill out this online form to have a Sentry Air Systems’ Applications Specialist contact you to discuss your process.

Resources
3 Brown, N. J. (1990). Health hazards manual for firefighters. Ithaca, NY: Cornell University, Chemical Hazard Information Program.
http://digitalcommons.ilr.cornell.edu/manuals/4