Exploding Aerosol Cans

NFPA SOB, Aerosol Products, classifies aerosol products into three hazard categories  

Sprinkler systems involving aerosols should be specifically designed by a fire protection engineer. In-rack sprinklers may be necessary, along with isolation of the product, fire doors, chain link fences, and special storage cabinets to protect the warehouse fi-om these hazards. 

Baled materials such as scrap paper or paper pulp can be deadly. Six firefighters died when piles of tissues that had soaked up sprinkler water collapsed. Some stored materials are packed with combustible strapping so that the bundles will collapse in a fire and aid in extinguishing the fire by smothering. Additional contents of high-racking storage could include flammables, flammable plastics, aerosols, and toxic chemicals. 

Ensure that fire hoses are not blocked in the warehouse. 

Fire protection in warehouses is a necessity. Data show that there are many warehouse fires each year that cost many millions of dollars. These losses do not have to occur if fire safety is taken seriously by management. 

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Caution should be observed if fire is involved in an incident, since many small containers can become projectiles as pressure builds up inside from the heat and the containers explode. Aerosol cans may be particularly dangerous because they are already pressurized, and exposure to heat can cause them to explode and rocket from the pressure. Those materials used in industry and institutions are usually service products used in cleaning and maintenance rather than in industrial chemical processes. 

A 250.-mL aerosol can at 25°C and 1.10 atm was thrown into an incinerator. When the temperature in the can reached 625°C, it exploded. What was the pressure in the can just before it exploded, assuming it reached the maximum pressure possible at that temperature ... 

Additional hazardous conditions can occur with aerosols or fine mists of combustible high flash point material. Mists of combustible liquids can readily explode. Mists can explode, just as combustible dusts will explode, even if the fluids in the mists are at temperatures well below their flash point. 

A typical aerosol can is able to withstand 10-12 atm without exploding. Objective 15... 

We can now explain why high temperature can cause an aerosol can to explode. If you leave an aerosol can in the hot sun, the temperature of the substances in the can will go up, and the rates ofevaporation ofthe liquids that it contains will increase. The concentration of vapor in the can will rise accordingly, and the vapor pressure will increase. If the pressure becomes too high, the can will explode. A typical aerosol can is built to withstand pressures up to about 10 to 12 times normal room pressure. 

Metallic aerosols can be made by passing a massive amount of electricity through a thin wire by discharging a bank of capacitors, whereupon the wire explodes." The technique, to which the name deflagration has been applied, was pioneered (as were so many things) by Michael Faraday," who converted a gold wire into powder by using the current produced by a Leiden battery. 

As the temperature of a fixed amoxmt of gas in a fixed volume increases, the pressure increases. In an aerosol can, this pressure increase can cause the can to explode, which is why aerosol cans should not be heated or incinerated. Table 11.2 summarizes the relationships between all of the simple gas laws and the ideal gas law. 

Aerosol containers can be dangerous if they are heated, because they can explode. Suppose a container of hair spray with a pressure of 4.0 atm at a room temperature of 25 °C is thrown into a fire. If the temperature of the gas inside the aerosol can reaches 402 °C, what will be its pressure, in atmospheres, if the volume and amount of gas do not change The aerosol container may explode if the pressure inside exceeds 8.0 atm. Would you expect it to explode ... 

Because the calculated pressure of 9.1 atm exceeds the limit of 8.0 atm, we would expect the aerosol can to explode. 

Figure 5-9. Aerosol cans will explode if heated. (Courtesy of the National Safety Council)...

True. Most aerosols contain flammable gas under high pressure. They can also explode if burnt, even when apparently empty. 

Any material that will burn in air in solid form may explode if it is dispersed in aerosol form. Explosions of foods, metals, pharmaceuticals, grain products, polymers, and other organic materials all have occurred in the past. Since oxidation is an exothermic reaction, the heat released in burning will rapidly raise the temperature of small particles nearby, and the large surface area presented by these particles encourages more reaction to take place and hence more heat to be produced. A runaway reaction can be the result. 

An empty aerosol-spray can at room temperature (20°C) is thrown into an incinerator where the temperature reaches 500°C. If the gas inside the empty container was initially at a pressure of 1.0 atm, what pressure did it reach inside the incinerator Assume the gas was at constant volume and the can did not explode. 

In Southeast Asia during the 1970s, symptoms began within minutes after an exploding munition (air-to-surface rocket, aerial bomb, cylinder) caused a yellow, oily, droplet mist to fall on individuals within 100 m of the explosion site. The falling droplet rain was inhaled, swallowed, and collected on skin and clothing contaminated the terrain and food and water supply and caused humans and animals to become acutely ill and to die after a variable period.7 Massive cutaneous contact was prevalent when the sources of exposure were sprays or coarse mists that were used deliberately to contaminate humans and the environment. Although the suspected trichothecene mycotoxin attacks in Southeast Asia would have involved multiple routes of exposure, we can postulate that the skin would have been the major site for deposition of a aerosol spray or coarse mist. 

Flammable liquids in small pressurized spray cans, such as paints, hair sprays, or engine cleaners, have the ability to explode from internal pressure when heated in a fire. The exploding cans create fireballs and are rocketing projectiles that leave a trail of burning liquid. Even a small quantity involved in a warehouse fire can have the potential to spread a fire and overtax the sprinkler system. Figure 5-9 illustrates a poster identifying the dangers of aerosols. 

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