1.

Introduction

Aerosols are collections of tiny particles of solid and/or liquid suspended in a gas. The
size of particles in an aerosol ranges from about 0.001 to about 100 microns. The most
familiar form of an aerosol is the pressurized spray can, commonly known as spray
cans, which can dispense anything from hair spray to enamel paint to whipping cream.

A wide variety of industries, businesses, government agencies and schools use

aerosol cans. Many cleaners, lubricants, paints, solvent and pesticides are packaged in
aerosol cans. A few example of aerosol cans used in daily life are deodorant spray, air
freshener, insect repellent and hair spray. In addition, households commonly generate
aerosol cans despite households are exempt from the hazardous waste regulations.

This assignment is to explore the origin of aerosol spray, to understand how

its made and how it works. Aerosol divided into four subgroups which each subgroup
have different scientific definitions. The effect of using aerosol spray on environment
and humans will be discussed thoroughly and proper way of waste management is
crucial to provide public awareness.

2.0

The History Of Aerosol Cans

The concept of aerosol dates all the way back to the late 18 th century when pressurized
carbonated beverages were introduced in France and in 1837 a man by the name of
Perpigna invented the valve that provided for an easier way of filling your cup. As
early as 1862, aerosol technology was being incorporated into metal cans for the first
time, but they were far too large and bulky to be of any practical use. In 1899,
Helbing and Pertsch patented the use of methyl and ethyl chloride as a propellant for
aerosols.

Erik Rotheim, a Norwegian engineer is responsible for designing the first

aerosol can and patented in 1931. The aerosol can is designed completely with a valve
that could hold products and dispense them with the use of propellants. However, the
Second World War is what really pushed aerosol technology in the direction of its
current form. His invention wasnt used popularly until WWII when it was used by
the military to hold insecticide, particularly in the Pacific, where mosquitoes were a
major issue, both as an annoyance and a spreader of disease.

During WWII the United States government had stationed hundreds of

thousands of soldiers and marines in the South Pacific and as a result of their activity
in this region, American militaries became highly susceptible to diseases, such as
malaria which is spread by mosquitoes. In order to find some way to protect them

servicemen from buzzing pests, the US government funded research to find some
portable technology to spray these disease carrying insects and thereby protect
American militaries in the South Pacific.

As a result of this funding, in 1943, two researchers from the Department of

Agriculture, Lyle Goodhue and William Sullivan developed a small portable can
pressurized by a liquid gas, a fluorocarbon, that was capable of spraying an antiinsecticide agent to combat the plague of insect-borne disease that was affecting
American servicemen in the South Pacific. These aerosol insecticides became
available to the general American public in 1947.

In 1949, 27-year-old Robert H. Abplanalps invention of a crimp on valve

enabled liquids to be sprayed from a can under the pressure of an inert gas. Spray
cans, mainly containing insecticides, were available to the public in 1947 as a result of
their use by U.S. soldiers for preventing insect-borne diseases. Abplanalps invention
made of lightweight aluminum made the cans a cheap and practical way to dispense
liquids foams, powders, and creams. In 1953, Robert Abplanal patented his crimp-on
valve "for dispensing gases under pressure." His Precision Valve Corporation was
soon earning over $100 million manufacturing one billion aerosol cans annually in the
United States and one-half billion in 10 other countries.

In the mid-1970s, concern over the use of fluorocarbons adversely affecting

the ozone layer drove Abplanalp back into the lab for a solution. Substituting watersoluble hydrocarbons for the damaging fluorocarbons created an environmentally
friendly aerosol can that did not harm the environment. This put the manufacture of
aerosol spray can products into high gear. Robert Abplanal invented both the first
clog-free valve for spray cans and the "Aquasol" or pump spray, which used watersoluble hydrocarbons as the propellant source.

In 1949, canned spray paint was invented by Edward Seymour, the first paint
color was aluminum. Edward Seymour's wife Bonnie suggested the use of an aerosol
can filled with paint. Edward Seymour founded Seymour of Sycamore, Inc. of
Chicago, USA, to manufacture his spray paints.

3.0

Classification of Aerosol

Aerosols are commonly classified into various subgroups based on the nature and size
of the particles of which they are composed and the manner in which the aerosol is
formed. The most important of these subgroups are fumes, dusts, mists, and sprays.
Further explanations of these four subgroups are as below:

3.1 Fumes
Fumes consist of solid particles which ranges in size from 0.001 to 1 micron that
suspended in a gas. Probably the most familiar form of a fume is smoke. Smoke is
formed from the incomplete combustion of fuels such as coal, oil, or natural gas.
The particles that make up smoke are smaller than 10 microns in size.
3.2 Dusts
Dusts also contain solid particles suspended in a gas, usually air, but the particles
are larger in size than those in a fume. They range from about 1 to about 100
microns in size, although they may be even larger. Dust is formed by the release
of materials such as soil and sand, fertilizers, coal dust, cement dust, pollen, and
fly ash into the atmosphere. Because of their larger particle size, dusts tend to be
more unstable and settle out more rapidly than do fumes, which do not settle out
at all.
3.3 Mists
Mists are liquid particles with a size less than about 10 microns that dispersed in a
gas form. The most common type of mist is that formed by tiny water droplets
suspended in the air, as on a cool sunny morning. If the concentration of liquid
particles becomes high enough to affect visibility, it is then called a fog. A
particular form of fog that has become significant in the last half century is smog.
Smog forms when natural moisture in the air interacts with human-produced
components, such as smoke and other combustion products, to form chemically
active materials.

3.4 Sprays
Sprays form when relatively large (10+ microns) droplets of a liquid are
suspended in a gas. Sprays can be formed naturally, as along an ocean beach, but
are also produced as the result of some human inventions such as aerosol can
dispensers of paints, deodorants, and other household products.
4.0

Aerosol Production Process

The process that goes into making a can of air freshener or bug spray was much more
complex than one might have thought. In addition to varying chemical formulations,
products differed on other dimensions, such as propellants, can sizes, and actuator
sizes. This variation among components increased the complexity of the scheduling
procedures at Spraytech. The process of making aerosol can is shown as below:
1.

Discs (slugs), the same diameter

as the finished aerosol can, are
punched
out
from
thick
aluminium sheet

2.

In the impact extrusion process a

slug is placed in the forming die
and is struck at high speed by a
reciprocating punch. The force of
the impact causes the metal to
flow, without addition of heat, to
form a closed end can.

3.

Trimmers remove the surplus

irregular edge and cut each can to
a precise specified height. The
surplus material is recycled.

4.

The trimmed can bodies are

passed through highly efficient
washers and then dried. This
prepares the internal and external
surfaces for coating and printing.

5.

The inside of each can is sprayed

with lacquer. This special lacquer
is to protect the can itself from
corrosion and its contents from
any possibility of interaction with
the metal.
6.

After heat curing the cans are

coated externally with a clear or
pigmented base coat which forms
a good surface for the printing
inks.

7.

The cans pass through a hot air

oven to dry the lacquer while
being conveyed on a pin-chain.

8. .

In the next step a decorator

applies the printed design in up
to eight colours, plus an
overvarnish.

9.

The cans are conveyed through a

second pin-chain oven which
dries the ink and varnish

10.

The last forming process is to

swage the top edge of the can in
approximately 15 steps to form a
smooth top and roll flange to
accept the aerosol valve/spray
mechanism.

11.

Every can is tested at each stage

of manufacture. At the final stage
it passes through a pressure tester,
which automatically rejects any
cans with pinholes or fractures.

12.

The finished can bodies are then

transferred to the warehouse to be
automatically palletised before
despatch to the filling plant.

5.0

How Aerosol Cans Work?

Aerosol can have it's mechanism designed to turn a liquid, such as paint or polish,
into a finely dispersed mist. If you've ever read the back of an aerosol can, you'll have
noticed messages such as "pressurized container" and "contents stored under
pressure." It is to ensure that something like paint comes out evenly when you press
the button on the top of an aerosol can, the manufacturers have to squeeze the contents
inside with a pump or compressor which is a bit like inflating a bicycle tire.

Typically, the contents of an aerosol are stored at 28 times normal

atmospheric pressure. That's why aerosols really rush out when you press their
buttons. It's also why aerosols feel really cold when you spray them on your body. If
you let a gas escape from 8 times its normal pressure into the air, it expands

enormously and cools down drastically. Gases cool when you let them expand because
the heat energy their atoms or molecules contain is spread over a much bigger volume.
Imagine a gas at a particular temperature: it has a certain amount of heat locked inside
it. Now spread that gas over a volume 8 times bigger. There's the same amount of heat
divided over a much bigger space, so each part of the space contains much less heat
than before it's cooler, in other words.

It is not easy to pressurize liquids, so just pumping something like liquid paint
into a can isn't going to make an aerosol that works properly. Fortunately, we can
pressurize gases very easily. So, in practice, aerosol cans contain two different
substances which is the liquid product which is the paint, detergent, hairspray, or
whatever it might be and a pressurized gas called a propellant that helps to push the
liquid product into the air and turn it into an aerosol cloud.

The propellant gas usually turns into a liquid when it's forced inside the can at
high pressure during manufacturing. That makes the propellant and the product mix
together and you can help to ensure they do so by shaking the can before you use it.
The propellant turns back to a gas when you push the nozzle and the pressure is
released. It disappears into the air leaving behind the product you're really interested
in.

An aerosol can would be entirely useless if there weren't some way of allowing
its contents to escape in a very controlled way. That job is done is by the valve at the
top of the can just underneath the button you press which has a spring to stop it
staying permanently open. When you force the button down against the pressure of the
spring, the valve opens and reduces the pressure at the top of the can, allowing the
contents to escape as an aerosol. Release the button and the spring closes the valve
again.

6.0

Environmental issue

A number of environmental problems have been connected to aerosols, the vast

majority of them associated with aerosols produced by human activities. Aerosol cans
contain both the product and a pressurized propellant. These products may have
hazardous characteristics, such as ignitability (used in paints or lubricants) or toxicity
(used in pesticides or chlorinated cleaning products). Additionally, most aerosol
containers pose an ignitability hazard because they contain highly flammable
propellants such as propane and butane. The pressurized aerosol cans themselves may
present a safety hazard under heat or pressure if not properly managed.
6.1

Effect on the Environment

A particularly serious environmental effect of aerosol technology has been damage to

Earth's ozone layer. This damage appears to be caused by a group of compounds
known as chlorofluorocarbons (CFCs) which, for more than a half century, were by
far the most popular of all propellants used in aerosol cans.

Scientists originally felt little concern about the use of CFCs in aerosol
products because they are highly stable compounds at conditions encountered on
Earth's surface. They have since learned that CFCs behave very differently when they
diffuse into the upper atmosphere and are exposed to the intense solar radiation
present there.
Under those circumstances, CFCs decompose and release chlorine atoms that,
in turn, react with ozone in the stratosphere (the atmospheric region approximately 7
to 31 miles above Earth's surface). As a result, the concentration of ozone in portions
of the atmosphere has been steadily decreasing. This change could prove to be very
dangerous, since Earth's ozone layer absorbs ultraviolet radiation from the Sun and
protects living things on our planet from the harmful effects of that radiation.
An article written by Daven Hiskey in 2011 entitled aerosol sprays do not
damage the ozone layer stated that aerosol sprays have not contained any known
ozone depleting substances for the last three decades. The misconception that aerosol
sprays damage the Earths ozone layer stems primarily from the fact that, originally,
aerosol cans used chlorofluorocarbons as a propellant. Chlorofluorocarbons were also
used commonly in refrigerators, air conditioners, and for many industrial applications.
Chlorofluorocarbons were particularly popular because they are non-flammable, nontoxic, and non-reactive to most compounds.
However, after scientists began to observe that the Earths ozone layer was
thinning beyond normal seasonal variations, in 1974, Nobel Prize winner Dr. F.
Sherwood Rowland and Dr. Mario Molina discovered that these chlorofluorocarbons

were the likely cause of the damage to the ozone layer, though this wasnt
conclusively proven until 1984.
Despite the lack of conclusive evidence, in the mid-1970s most manufacturers
voluntarily stopped using chlorofluorocarbons. Further, in 1978, chlorofluorocarbons
were officially banned in the United States, with a few exceptions. These exceptions
were primarily concerning certain medical applications, such as with asthma inhalers
(though use in inhalers and other medicinal applications were officially banned in
2008).
Other countries quickly followed the U.S. in banning the use of
chlorofluorocarbons, including Canada, Mexico, Australian, and many European
nations. The Montreal Protocol agreement has been ratified by 70 countries initially
and 196 countries to date, production of chlorofluorocarbons, along with other ozone
damaging substances, began to be phased out altogether starting in 1996, the
completion of which, even in many developing countries, took place in 2010.
Todays aerosol products improve our quality of life in many ways. They
provide benefits in medical treatment, health care, pest control, disease prevention,
personal care and hygiene, and household automotive and industrial cleaning and
maintenance.
Aerosol containers give consumers the use of products unavailable in any
other form. Only an aerosol container can provide the variation of propellant pressure
and the wide range of spray patterns and particle sizes that make possible products
specially designed for specific consumer needs such as:

i.

Long-distance spray insecticides protect humans from harmful insects without

ii.

exposure to bites or stings.

Asthmatic inhalers produce a mist fine enough to penetrate deeply into the

iii.

bronchial area
Specially formulated insecticides penetrate behind cabinets and walls to

iv.

remove vermin in homes, schools and work areas.

First aid products can be applied without direct contact and can protect the

v.

damaged area from air contact.

Lubricating products can be applied to hard-to-reach machine parts and to

vi.

machinery in operation.
Contact lens solutions in a spray form eliminate the need to touch the lens

vii.

itself.
Stable foam products, such as shaving cream and furniture polish, cannot be
created in any other way.

6.2

Effect on Human Health

The dangers of aerosol sniffing

Another risk associated with commercial aerosols is their use as recreational drugs.
Inhalation of some consumer aerosol preparations may produce a wide variety of
effects, including euphoria, excitement, delusions, and hallucinations. Repeated
sniffing of aerosols can result in addiction that can cause intoxication, damaged
vision, slurred speech, and diminished mental capacity.

Figure 6.1: news on about effect of antiperspirants

In 2011, a 16 year old teenage boy died from heart attack. A post-mortem
examination showed the poor boy had ten times the lethal amount of butane and
propane in his blood. The gases are used as aerosol propellants and it seemed they had
built up in his body over many months. A consultant heart specialist at the Royal
Brompton Hospital stated that the main cause of death is usually suffocation, known
as hypoxia. If oxygen is not being breathed in and something else is inhaled, such as
chemicals, then suffocation occurs and the heart stops. The coroner ruled that the
death was accidental by excessive use of antiperspirants.
In 2008, a 12 year old boy collapsed after using spray deodorant in the
bathroom of his home in Sandiacre, Nottingham. He died in hospital five days later, in
January 2008. The coroner reported that his death had been caused by a cardiac
arrhythmia, exacerbated by exposure to solvents. The solvents in the antiperspirants

aerosol he had been using had triggered an unknown pre-existing heart arrhythmia and
caused a fatal collapse.
Besides, aerosol burn injuries can be caused by the spraying of aerosol directly
onto the skin, in a practice sometimes called "frosting". Adiabatic expansion causes
the aerosol contents to cool rapidly on exiting the can.
7.0

Aerosol Spray Can Waste Disposal Procedure

Aerosol Brake Cleaner used in the various professional industries is packaged in

aerosol spray cans. These Aerosol cans are thin-walled steel containers pressurized
with one of several types of hydrocarbon propellants, such as butane. When the
aerosol can is empty, the propellant and product are gone; the cans that remain are not
considered hazardous wastes by themselves. However, partially empty aerosol spray
cans maybe regulated as hazardous wastes because they contain ignitable solvents.

7.1

Recycling

Under the federal Resource Conservation and Recovery Act (RCRA), aerosol cans
may be recycled if they have been emptied through normal use or punctured and
drained to remove significant liquids. Some states such as California have more
stringent regulations than RCRA. Be sure to investigate your own state regulations
before recycling aerosol cans. The shops are responsible for properly managing any
captured wastes recovered from puncturing and draining.

Although spray cans may be discarded in the trash, they are recyclable due to
the fact that the majority of the can is steel; in fact, the typical spray can contains at
least 25% recycled steel. A number of recyclers that collect drained oil filters for
recycling will also accept empty spray cans along with the filters. The oil filters and
spray cans are shredded and melted down to make new steel.
7.2

Managing empty aerosol containers

Empty means the can contains no product and no pressure. Empty containers are
exempt from hazardous waste rules. They have no special storage, labelling or
disposal requirements. Recycle them, if possible, or send them to an incinerator that
will recover the metal. If you have a small number of empty aerosol containers, they
may be able to be mixed with your solid waste.
7.3
Managing Non-empty Aerosol containers
First, try to return or exchange malfunctioning aerosol spray cans. Malfunctioning
aerosol spray cans return to the supplier or manufacturer are considered product not
waste. Hazardous waste rules do not apply. You must follow applicable Department
of Transportation (DOT) requirements for transport. Non-empty aerosols that cannot
be returned or exchanged must usually be managed as a hazardous waste. Regardless
of the contents, most aerosols are hazardous because they are ignitable due to the type
of propellants used.

References
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May 2015.
Aerosol can management. Delaware Department of Natural Resources and
Environmental Control, Solid & Hazardous Waste Management Section.
Aerosol Spray Can Management. (2009). State of Oregon department of environment
quality.
Aerosol Spray Can Waste Disposal Procedure. (2015). Retrieved from
http://www.renegadepartswashers.com/health_and_safety/aerosol_spray_can_
waste_disposal_procedure.htm on 4 May 2015.
Bellis,

M. The History of Aerosol Spray Cans. Retrieved from

http://inventors.about.com/od/astartinventions/a/aerosol.htm on 29 April 2015.

The hidden dangers deodorant sprays headaches, eczema, asthma even fatal heart
problems. (2011). Retrieved from http://www.dailymail.co.uk/health/article2402692/The-hidden-dangers-deodorant-sprays-Headaches-Eczema-AsthmaEven-fatal-heart-problems.html on 1 May 2015.
The

history
of
the
aerosol.
http://www.yorks.karoo.net/aerosol/link1.htm

Retrieved

from

Todays
aerosol.
(2013).
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from
http://www.aerosolproducts.org/environment/ on 4 May 2015.
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