Heat and Temperature Study Guide for McGraw-Hill's Firefighter Exams
Heat and temperature are two distinct, but closely related, concepts. Heat is a measure of the quantity of energy contained in a substance. It is the total amount of molecular vibration (energy) in a material. Temperature, on the other hand, is the average energy of its molecules. Temperature is a measure of how fast molecules are moving within a substance. It is an indicator of the level at which the heat energy exists.
Heat is measured in several ways, discussed briefly below.
British Thermal Unit
A British thermal unit (BTU) is the amount of heat energy required to raise the temperature of 1 lb of water (measured at 60°F at sea level) by 1° F. Common materials that burn store a standard amount of heat energy per pound. This information is valuable to firefighters when they are calculating the amount of water required during fire extinguishing operations and to fire protection engineers when they are designing and installing fire extinguishment systems and equipment.
One BTU is equal to 252 calories (metric heat unit), 3.96 large calories (kilogram calorie), or 1,055 joules (mechanical heat unit). Below is a list of some common combustibles and their equated latent heat of combustion:
A calorie is the amount of heat energy required to raise the temperature of 1 gram of water (measured at 15 degrees Celsius [°C] at sea level) by 1° C. One calorie is equivalent to 4.184 joules.
The joule is the heat energy unit in the International System of Units (SI). It is the amount of heat energy provided by 1 watt flowing for 1 second.
Temperature units can be used to compare the difference in heat energy levels between two materials. Temperature is measured by monitoring how much an object expands from its size at a given starting point (the freezing point of water, for example) and defining a unit of measurement (1 degree). All temperatures are then multiples of that defined unit of measurement.
The Fahrenheit (F) degree is named for the German scientist Daniel Gabriel Fahrenheit, who invented the thermometer at the beginning of the eighteenth century. There are 180 increment degrees between the temperature of melting ice (32 degrees) and the boiling of water (212 degrees) on the Fahrenheit temperature scale. 1°F is equal to 5/9 degrees Celsius.
To convert (approximately) a temperature on the Fahrenheit scale to the Celsius or Centigrade scale, you first subtract 32 degrees from the Fahrenheit temperature and then multiply by 5/9.
For example, if a person's body temperature is 98.6°F, its temperature in Celsius is
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