firefighter i. 2 copyright and terms of service copyright © texas education agency, 2011. these...

Physical States of Matter and the Combustion Process

Firefighter I

2

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Vapor Density

The weight of a given volume of vapor or gas, compared to an equal volume of dry air at an equal vapor pressure

All vapors and gases mix with air The vapor density of air is 1

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Vapor Density (continued)

The vapor density of air is 1Gases with vapor density

Less than air, rise and dissipate

Greater than air, sink and accumulate



Vapor Density (continued)

Some common flammable gases



Specific Gravity

The weight of a substance compared to the weight of an equal volume of water at an equal temperature



Specific Gravity (continued)

Substances with a specific gravity

Lighter than water, float

Heavier than water, sink




Water and most flammable and combustible liquids don’t mix with each other (immiscible).

Hazardous because the flammable fuels will float on the water where they could ignite or burn

Important when considering firefighting tactics and strategies and the limits placed on extinguishment options




Flammable liquids burning on top of water in a tanker spill that occurred in 1991.



Surface-to-Mass Ratio

The surface area of a fuel in proportion to its massThe higher the

surface-to-mass ratio of a fuel, the higher its ignitability



Surface-to-Mass Ratio (continued)

A piece of plywood on its edge exposes 3 surface areas

Orientation of a fuel matters!



Heat Release Rate (HRR)

Affected by surface-to-mass ratio

Depends on fuel type, fuel quantity, and the orientation of the fuel

Increases as more fuel becomes involved in the combustion process



Narcotic AsphyixiantGases and Irritants

Most fire-related deaths are caused by smoke

Smoke is made of gases, vapor, and soot (solid particulates) that are inherently poisonous

Regard all smoke as toxic and hazardous 13

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Common Products of Combustion

Carbon monoxide (CO) Hydrogen cyanide (HCN) Carbon dioxide (CO2) Irritants Particulates



Carbon monoxide (CO)

A byproduct of the incomplete combustion of fuels containing carbon The most common product of combustion

found at structure fires The leading cause of civilian fire deaths A chemical asphyxiate that binds with

hemoglobin, inhibiting oxygen transfer



Hydrogen Cyanide (HCN)A byproduct of combustible fuels containing nitrogen A chemical asphyxiate

that prevents the body from using oxygen at the cellular level

Most associated with the combustion of polyurethane foam, which is commonly found or used in furniture and bedding



Carbon Dioxide (CO2)

A byproduct of complete combustionNot considered to be toxic, but it can

act as an asphyxiate by displacing oxygen

Also acts as a respiratory stimulant by increasing the respiratory rate of its victims



Irritants

Byproducts of combustion that can Make breathing difficult and

uncomfortable Inflame the eyes,

respiratory tract, and skinSmoke can carry different

and varied irritants, depending on the fuel source



Particulates

Byproducts that can be inhaled and deposited in the mouth, trachea, and lungs May cause respiratory

distress and irritation to the eyes

There may be additional health hazards specific to the fuels being burned



Resource

0135151112, Essentials of Firefighting (5th Edition), International Fire Service Training Association (IFSTA)

Images used with permission by IFSTA.



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