Aerosol Laboratory
Safety
Aerosol Stability Ovens—Uses & Cautions
This column focuses once again on safety—specifically, the
aerosol stability storage oven. Storage ovens are used to
raise the temperature of an aerosol product to evaluate
product/package stability. The intention is to accelerate potential
corrosion and/or other chemical processes so that any adverse effects
can be detected more rapidly in this controlled environment
versus “real time” in the field.
Products tested for product/package compatibility are often
stored in elevated temperature ovens ranging from 100°F–130°F
(37.7°C–54.4°C). The intent is to simulate the real-world high
temperature exposure that aerosol products may be exposed to
(i.e. pallets of product in warehouse storage, individual cans stored
in the trunk of vehicle on a hot day, etc.).
As has been my practice in these articles, I will share a personal
disaster story relating to today’s topic. As you might imagine, after
39 years in this industry, I have a sizeable collection of examples.
Thirty-five years ago, I was working as a product development
supervisor in the Boyle-Midway research laboratory. Major brands
included Woolite, PAM, Black Flag, Wizard Air Fresheners, Easy
Off Oven Cleaner, Speed Starch and 3-in-1 Oil, among others.
One sunny day I was working at my desk in the lab area along
with two other aerosol chemists. Our quiet focus was disturbed by
three violent explosions in rapid succession. As I turned toward
the disruption, I observed a fireball scorching the ceiling tiles and
smoke billowing out of a temperature controlled benchtop stability
storage oven.
In rapid order, the fire alarm was pulled and the building was
evacuated. The good news was that no one was injured. The
cleanup and incident investigation then began. It is the results of
this investigation, the lessons learned and the corrective actions
instituted that I would like to share.
John ChadwiCk
aerosol Technical Solutions
www.SprayNow.com
The cleanup phase revealed that the oven door was blown
open, destroying the metal latch. I note that these were the “good
old days” when metal latches were well-built; a significant amount
of force had needed to be generated to break open that latch.
Five filled aerosols were stored in the oven and all were rated
“flammable” as they were pressurized with hydrocarbon propellant.
Three of the cans exploded; two remained intact. The cans
were steel three-piece containers and components of all three were
found in different parts of the lab, from 10 to approximately 30
feet from the oven. The can components struck various objects
and surfaces leaving “witness marks”—dents, scratches and holes
in some of the surfaces they struck. Again, we were fortunate that
no one was injured.
This particular oven was set to 130°F (54.4°C) and used for
short-term (typically one month) corrosion spot checks of prototype
formula/package combinations. Evaluations included AI
degradation, fragrance stability and an initial read on potential
corrosion issues.
You may be thinking, “Isn’t 130°F a bit excessive?” My personal
opinion, after setting up and evaluating numerous stability tests
with a wide variety of aerosol product types, is that the “shortterm”
high temperature (100°F–130°F) screening of prototype
aerosol products is quite useful for research purposes. I note that
this is distinct from the full-term aerosol stability packs that are
used to test final/production-ready aerosol prototypes; the typical
protocol for this testing is a two-year test plan, with multiple
checkpoints and storage temperatures. The 130°F storage parameter
is typically set up for one month, at which point the cans are
cooled to room temperature and evaluated.
Furthermore, issues observed in the short-term screening test
may not necessarily eliminate a product/package variable. In
24 Spray November 2019
Safety training and
requirements—as well as
equipment verification and
maintenance procedures—
are important, especially
when flammable aerosols
are being stored…