Combustible Ignition Fire Protection

QUESTION

Consider the following statement: “Combustible ignition can result when any combustible material is heated by a low temperature source over a long period of time.” Interview fire investigation personnel in your jurisdiction or community about their experience with this concept.

Next, independently research the published and/or online literature related to this concept. Discuss whether your research findings support or refute the information revealed in your interview(s) with professionals in the field.

ANSWER

“Combustible ignition can result when any combustible material is heated by a low-temperature source over a long period of time”

Combustion or ignition refers to the exothermic chemical reaction between a combustible material, which is also known as a fuel, and an oxidant. Combustion results in the production of heat and the conversion of chemical species. Fire is the result of ignition and combustion of a fuel. Ignition of an object occurs when the ignition temperature of the object is achieved. Ignition temperature, also known as the autogenous ignition temperature, is the lowest temperature at which an object or substance takes fire when heated in the air, and continues burning. Objects and substances that can catch fire and burn are referred to as combustible of flammable substances and objects. Substances that can burn are classified as either flammable or combustible on the basis of their flashpoints, which refers to the lowest temperature at which they are ignited or start burning. A substance that ignites or catches fire and burns at normal working temperatures is classified as flammable, while a substance that has the ability to be ignited and burn at a temperature that is above the normal working temperatures is classified as a combustible substance (Russell & Cohn, 2012).

Combustible and flammable substances are classified using various criteria. However, the most common standard is that substances that have a flashpoint that is below 100°F or 37.8⁰C are flammable (Canada, 2015), while those having a flashpoint that is above 100°F and below 200⁰F are classified as combustible substances (Smith, 1988). Combustible ignition is, therefore, the ignition or the catching of fire of a material that is combustible. Combustible and flammable substances are present in all workplaces and homes and include substances such as common solvents, adhesives, waxes, and building materials. While flammable materials only require exposure to low temperatures to ignite or catch fire, combustible materials require exposure to higher than normal working temperatures to ignite. This is because combustible materials have a high flashpoint temperature, which means that they only catch fire and burn when exposed to temperatures that are above their flashpoint.

When a combustible material is exposed to a heat source that is at, for instance, 75°F, the material will not ignite. No burning will occur. If a flammable material is exposed to the 75°F temperature, it will ignite because its flashpoint may be 45°F. Combustible ignition will only occur when the heat source present gives off high temperatures. Upon consulting various fire investigation and fire-fighting personnel, I was able to understand that sometimes a combustible material may be ignited by a low-temperature source. The fire experts that I engaged in conversation explained how continuous exposure to low temperature can result in the ignition of combustible materials. According to the fire investigation experts and the research that I conducted online (Welzel et al., 2000), prolonged exposure of a combustible material to a low temperature heat source may result in ignition if the exposure to the low heat source is long enough to raise the temperature of the combustible material to its flashpoint or ignition temperature.

If a combustible material that has a flash point of 120°F is exposed to a heat source that is at a temperature of 90⁰F, there will be no combustible ignition immediately, as the temperature of the source is below the flashpoint of the material. However, if the material remains exposed to the heat source for a long period of time, without removal, the temperature of the material will gradually rise, especially if the material is a good conductor of heat. If the heat source is not withdrawn before the temperature of the material reaches 120⁰F, the material will ignite. This way, combustible ignition can occur when combustible materials are heated by a low-temperature source over a long period of time. However, if the material does not conduct heat, there will be no ignition, as its temperature will remain constant and not gradually rise to reach the flashpoint.

References

Canada, H. (2015, March 23). WHMIS 1988. Retrieved May 31, 2019, from https://www.canada.ca/en/health-canada/services/environmental-workplace-health/occupational-health-safety/workplace-hazardous-materials-information-system/whmis-1988.html

Russell, J., & Cohn, R. (2012). Workplace Hazardous Materials Information System (WHMIS). Book on Demand.

Smith, D. L. (1988). WHMIS at the work site. Occup. Health Saf. Magazine, 12, 6-8.

Welzel, M. M., Schenk, S., Hau, M., Cammenga, H. K., & Bothe, H. (2000). Ignition of combustible/air mixtures by small radiatively heated surfaces. Journal of hazardous materials, 72(1), 1-9.