Aerosols and Their Small-Scale Production
7 minute read
What you will learn
- Define an aerosol and a pressurised pack
- Name the parts of an aerosol container
- Describe the types of propellant
- Describe how aerosols are filled
- State the safety rules for aerosols
- Calculate the number of days an inhaler lasts
Key points
- An aerosol is a product packed under pressure, with a propellant that pushes out the contents through a valve.
- The parts are the container, valve, actuator (button), dip tube, product concentrate and propellant.
- Propellants are liquefied gases or compressed gases. Chlorofluorocarbons (CFCs) have been phased out because they harm the ozone layer.
- Types include space sprays, surface sprays, foams and metered-dose inhalers.
- Aerosols can be filled by cold filling or pressure filling, in controlled conditions.
- Containers are pressurised and many propellants are flammable, so they must not be heated, punctured or burned.
- Metered-dose inhalers deliver a set dose per puff, so technique matters.
What is an aerosol?
An aerosol is a product packed under pressure in a container with a propellant. When the valve is opened, the propellant forces the contents out as a fine spray, mist, foam or stream. The term is also used for the container itself, the pressurised pack.
Parts of an aerosol
| Part | Function |
|---|---|
| Container | A strong metal (or sometimes plastic-coated glass) can that holds the pressure |
| Valve | Opens and closes to release the contents. A metering valve releases a fixed dose |
| Actuator | The button or nozzle that is pressed, and shapes the spray |
| Dip tube | Carries the product from the bottom of the can to the valve |
| Product concentrate | The drug, solvent and other ingredients |
| Propellant | Gas that creates the pressure and pushes the product out |
Propellants
| Type | Notes |
|---|---|
| Liquefied gases | Stored as a liquid under pressure, and turn to gas when released. Hydrocarbons (such as propane and butane) are common, but they are flammable. Hydrofluoroalkanes are used in many inhalers |
| Compressed gases | Gases such as nitrogen or carbon dioxide. The pressure falls as the can empties |
| Chlorofluorocarbons (CFCs) | Used in the past. Phased out because they harm the ozone layer |
Types of aerosol
| Type | Use |
|---|---|
| Space sprays | Fine mist in the air, such as air fresheners and insecticides |
| Surface sprays | Applied to a surface, such as skin sprays, wound sprays and antiseptic sprays |
| Foams | Product comes out as a foam, such as some creams and shaving products |
| Metered-dose inhalers (MDIs) | Deliver a measured dose of drug to the lungs with each puff, such as asthma inhalers |
Small-scale production
Aerosols are made in specially controlled conditions, because of the pressure and the fire risk.
Cold filling
- The concentrate and the propellant are cooled so that the propellant is liquid at normal pressure.
- The cooled concentrate is put into the container.
- The cooled propellant is added.
- The valve is fitted and crimped on straight away.
Pressure filling
- The concentrate is placed in the container.
- The valve is fitted and crimped on.
- The propellant is forced in through the valve under pressure.
Both methods need the right equipment and training, with ventilation, no ignition sources and checks for leaks. Finished cans are checked, often by passing them through a warm water bath to find leaks.
Other non-pressurised sprays, such as pump sprays, are also used. They do not need a propellant and are simpler to make.
Safety
- Do not heat, burn or puncture an aerosol, even when it looks empty.
- Keep away from flames and heat, and do not use near a fire.
- Store in a cool place, out of direct sunlight, below the temperature given on the label (often 50 °C).
- Keep out of the reach of children.
- Do not spray near the eyes or face unless the label says so.
- Use in a ventilated place.
- Do not inhale deliberately, which is dangerous.
Patient advice for inhalers
- Shake the inhaler, if directed.
- Breathe out, put the mouthpiece in the mouth, press and breathe in slowly, and hold the breath for about 10 seconds.
- Wait about a minute between puffs.
- A spacer helps, especially for children.
- Rinse the mouth after using a steroid inhaler.
- Check the dose counter, and replace the inhaler before it runs out.
Example. The inhaler has 200 puffs. The dose is 2 puffs twice daily.
- Daily puffs = 2 × 2 = 4
- Days of supply = 200 ÷ 4 = 50 days
Exam focus
- Name the parts of an aerosol and state the function of each.
- State two safety rules for aerosols.
- Calculate the number of doses or days of supply from an inhaler.
- Common mistake: forgetting that aerosol cans are pressurised and must be kept away from heat.
Quick check
Test yourself before you move on. Pick an answer to see the explanation.
1.The function of the propellant in an aerosol is to:
2.Which of these is a safety rule for aerosol cans?
3.An inhaler contains 200 puffs. The dose is 2 puffs twice daily. How many days does it last?
4.CFC propellants were phased out because:
5.The button that is pressed to release an aerosol is called the: