Week 3 Forum – Ignition
Ignition is the process of initiating self-sustained combustion. Once ignition occurs, heat transfer becomes important in the growth and spread of a fire.
Once you complete the Week 3 readings, write a post to achieve the following:
1. Briefly discuss what it takes for ignition to occur in a solid, liquid, and gas.
2. Define, compare and contrast the different modes of heat transfer.
3. Provide one example of each mode of heat transfer and discuss why it is a fitting example for that mode.
#1
The forum discussion for this week is to discuss what it takes to ignite a solid, a liquid and gas. We will also be discussing the different modes of heat transfer and providing examples of each mode of heat transfer.
When we discuss what it takes to ignite items, we first need to know the definition of ignition temperature. Ignition temperature is the minimum temperature required for ignition of fuel gases. There are several other ways to measure ignition in solids, liquids and gases they are piloted ignition temperature, auto ignition temperature and minimum ignition energy. For a solid to ignite they must ossify first, most solids need to reach a certain ignition temperature before combustion takes place. Liquids have a flash point that causes combustion, as we know from our readings this week the liquid itself does not burn it is usually the vapors from the liquids that burn. Gases ignite and burn when they enter a chemical reaction that causes the correct amount of oxygen to be present for ignition of the gases.
When we speak of heat transfer, we need to look at three main types, conduction, convection and radiation. Conduction is defined as the transfer of energy in the form of heat by direct contact through the excitation of molecules and or particles driven by a temperature difference. Convection is defined as the transfer of energy through a circulating fluid to or from a solid object. Radiation is defined as the transfer of energy through the electromagnetic waves.
An example of conduction is a firefighter transferring his or her body heat in full turn out gear to a solid surface such as a floor while crawling. An example of conduction is placing an article on a radiator, the article will become warm. This example of conduction is important in the fire service as items placed on a radiator could cause a fire. An example of radiation pertaining to the fire service is a candle burning emits radiation, this burning candle could lead to a fire.
References:
Radiation / Conduction / Convection. (2005). Retrieved from http://search.credoreference.com/content/entry/hmcontempusage/radiation_conduction_convection/0
#2
Throughout the past few weeks we have covered various topics in the field of fire protection all of which hold importance in some way or another. This week we move on to the topic of the ignition and all its various nuances. In order for ignition to occur in a liquid, gas, or solid there are certain prerequisites that must be in place. To understand the topic of ignition one first understand the elements of the fire tetrahedron. The elements needed are fuel, heat, oxygen, and self sustained chemical reaction. According to an article published by the University of Auburn the best example of an ignition source is a match. The article states that the common household match exemplifies this, “Fire begins with ignition. The match is a common ignition device. Friction creates sufficient heat to ignite the phosphorus on the end of the match. Combustion occurs and the match flames” (Auburn,2018).
Once ignited there are various forms of heat transfer that can occur as well. They are conduction, convection, and radiation. Conduction is through solids, liquids and gasses are convection, and radiation is the final mode. Conduction can best be illustrated by would be a firefighter touching the hot floor in the event of a fire, hopefully with gloves. Conduction is the process by which the hot air is transferred by flowing over, such as the super heated gasses escaping a door in a fire. The final transfer is radiation which can be illustrated by the heat coming off of a flame. One of the best illustrations that I found online is listed below and shows all three phases.
References:
Anderson, H. E. (1969). Heat transfer and fire spread. Res. Pap. INT-RP-69. Ogden, Utah: US Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 20 p., 69.
Auburn University. (2018). The Combustion Process. Retrieved from http://www.auburn.edu/academic/forestry_wildlife/fire/combustion.htm