Aerosols expert witnesses may write reports and opine on aerosol sprays, airborne solid particles, and household chemicals. The National Aerosol Association describes how an aerosol works:
The aerosol package is a self-contained dispensing system with three main elements:
1. Active Ingredients (soap or disinfectant, etc.)
2. Inert or Inactive ingredients (water)
3. Propellant
The propellant is a gaseous compound which pushes the product out of the container and produces a spray or foam. In most cases, the propellant also acts as a solvent to keep the product at the proper strength. In the United States, the most common propellants are naturally occurring hydrocarbons. A few products, about 10% of today’s aerosols, use compressed gases like carbon dioxide and nitrous oxide as propellants.The final element is the container, which is usually a steel or aluminum can. The leak-proof can protects the product from contamination and evaporation.
All of these pieces work together based on simple scientific principles. An aerosol package is an air-tight, pressurized container. Pressing the actuator button opens the valve. Since the pressure outside the can is less that the pressure inside, the propellant expands, pushing the product up the dip tube and out through the valve. This system allows the product to be applied in a variety of ways; in a fine mist, a metered spray delivering just the right amount, foam, or even a long distance spray.