1.0 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

it’s 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 18th 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 wasn’t 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 anti-

insecticide 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 water-

soluble 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 water-

soluble 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.

2.

Discs (slugs), the same diameter as the finished aerosol can, are punched out from thick aluminium sheet

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.

4.

5.

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

The trimmed can bodies are passed through highly efficient washers and then dried. This prepares the internal and externalsurfaces for coating and printing.

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.

7.

After heat curing the cans are coated externally with a clear or pigmented base coat which forms a good surface for the printing inks.

The cans pass through a hot air oven to dry the lacquer while being conveyed on a pin-chain.

8. .

9.

In the next step a decorator applies the printed design in up to eight colours, plus an overvarnish.

The cans are conveyed through a second pin-chain oven which dries the ink and varnish

10.

11.

The last forming process is to swage the top edge of the can inapproximately 15 steps to form a smooth top and roll flange to accept the aerosol valve/spray mechanism.

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.

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.

The finished can bodies are then transferred to the warehouse to beautomatically palletised before despatch to the filling plant.

Typically, the contents of an aerosol are stored at 2–8 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 Earth’s 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, non-

toxic, and non-reactive to most compounds.

However, after scientists began to observe that the Earth’s 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 wasn’t

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.

Today’s 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

exposure to bites or stings.

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

bronchial area

iii. Specially formulated insecticides penetrate behind cabinets and walls to

remove vermin in homes, schools and work areas.

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

damaged area from air contact.

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

machinery in operation.

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

itself.

vii. 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

Aerosol. Retrieved from http://www.scienceclarified.com/A-Al/Aerosols.html on 1 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/article-2402692/The-hidden-dangers-deodorant-sprays-Headaches-Eczema-Asthma-Even-fatal-heart-problems.html on 1 May 2015.

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

Today’s aerosol. (2013). Retrieved from http://www.aerosolproducts.org/environment/ on 4 May 2015.

Weide, R. Spray Paint: How an Object Became an Object and a Subculture.