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 Firefighters
says “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
http://digitalcommons.ilr.cornell.edu/manuals/4
http://digitalcommons.ilr.cornell.edu/manuals/4
No comments:
Post a Comment