What is Flammability?
Flammability is a measure of how quickly a specific material is capable of catching fire and burning. It indicates the ease with which a material can ignite and the intensity with which it burns once it catches on fire.
Materials that are highly flammable must be treated with extra care, as they can combust quickly. To accurately determine the flammability of a material, fire testing is often conducted. In normal terms, materials are often rated as either:
- Highly flammable
The safety data sheet often contains a list of all the physical and chemical properties of materials used in the workplace, and section 9 generally contains information about the item’s flammability.
Why Is It Important to Conduct Flammability Testing?
It’s very important to determine the flammability of a substance to burn to ensure the safety of employees on a work site or in a factory. There are many materials that are highly flammable, as long as certain conditions are met.
Therefore, depending upon the conditions, properties can change. Once a material or chemical ignites, it can then sustain combustion on its own. As a result, the heat generated by the material when it’s exposed to oxygen should be enough to overcome any loss of heat.
Depending upon the geometry, the environment, and the condition of the material or chemical, its ability to sustain a burn will vary. In most cases, flammability refers to the burning in fresh air. However, in an environment with pure oxygen, many chemicals that aren’t generally considered flammable tend to ignite and burn quite easily.
Therefore, gauging the flammability of different materials is critically important for several reasons. To mitigate the risk of a fire outbreak or an explosion, companies conduct flammability testing.
This is done to evaluate some important attributes of the material itself, such as its lower flammability limit, limiting oxygen concentration, upper flammability limit, or the deflagration index. Here’s a brief description of these terms:
- Lower flammability limit (LFL): This indicates the lowest concentration at which a flammable gas, solid, or liquid can be considered flammable in open air.
- Upper flammability limit (UFL): This indicates the highest concentration at which a flammable gas, solid, or liquid can be considered flammable in open air.
- Deflagration Index: This is simply the rate of pressure at which a flammable substance can be allowed to escape without causing an explosion. It’s widely considered as an explosion protection measure.
- Limiting Oxygen Concentration (LOC): This determines the minimum amount of oxygen needed for a material to catch on fire.
Companies often conduct different types of flammability tests to determine the fire properties of materials. These include:
- Susceptibility to ignite
- Burn rate
- Flame spread
- “Flash over” point
- Combustion capabilities
Vertical and Horizontal Flammability Tests
Flammability testing is commonly used to determine a substance’s burn rate or how it reacts. In most cases, either vertical or horizontal flammability tests are conducted. The materials are kept on a Bunsen burner, either in a horizontal or vertical formation.
Then, once the material ignites, the source of the ignition is removed, and then experts evaluate factors such as:
- Release of combustive gas
- Total loss of mass
- Smoke opacity and density
- Measuring the heat release
These tests are often conducted when a product is passing through its research and development stage. In some cases, flammability testing is also required to ensure that a product meets regulatory, industry, or commercial standards.
Flammability tests also take into account several variables, including:
- The amount of oxygen in the environment
- Ignition energy
- Pressure within the vessel
- Size and overall dimensions of the vessel
- The chemical composition of the gas released
In some cases, flammability tests are properly designed, with specific vessels prepared depending upon the type of material to be tested. These can include spherical, large, small, or cylindrical vessels.
Flammability of Gases
It’s incredibly easy to define gases in terms of how flammable they are. In a mixture of gas and air, there’s always a lower flammability limit, at which the gas doesn’t burn. For instance, when you consider hydrogen, the lower flammability limit is 4% based on volume.
Flammable gases require air to burn, and once the concentration of air reaches a certain threshold, the gas can no longer sustain its burn. In most cases, the presence of other gases can also affect the flammability of a gas.
Flammability of Liquids
In general, it’s the vapor that burns than the liquid itself. In order for a fire to light up, the concentration of vapor in the air needs to be greater than the lower flammability limit. The temperature of the liquid itself plays an important role here, as do the geometry and the conditions in the environment.
The temperature at which the liquid ignites is referred to as the flash point. And, to sustain the fire once it ignites, it’s important that it generates sufficient vapor. The minimum temperature at which this happens is known as the fire point.
Flammability of Solids
Solids tend to ignite and burn due to the volatile gases that release from the material of the solid surface. Thus, the ambient conditions play an important role here. In most cases, solids burn well when heat loss is reduced and the amount of surface area to mass is higher.
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