Launch of our new factfile on arc flash risk management

the conversion between Joules and calories is not linear with temperature.

No, it isn't, but the effect is frankly piddly, the various calories are named after the temperature of the test.

The most common “15° calorie” (also called the gram-calorie, or small calorie) was defined back when the UK recognised such units as the amount of heat that will raise the temperature of 1 gram of water from 14.5° to 15.5°C—equal to 4.1855 joules. Other less common definitions in this series were the 20° calorie (4.18190 joules) from 19.5° to 20.5° C; and the “mean calorie” (4.19002 joules) defined as 1/100 of the heat necessary to raise the temperature of 1 gram of water from 0° to 100°C.

For nearly all practical purposes, the heat capacity of water is constant, and the conversion factor is approx 4.2 joules per calorie. This applies at all common temperatures used to define the calorie.

Then to confuse matters, dieticians use the word “calorie” for kilocalorie, and are therefore  1000 times higher.  (a Mars bar and a small stick of dynamite are both  about 1 megajoule, so something like 230 diet calories, and 230 000 real ones… by the way  it is really important to note that the rate of energy release during combustion differs by about 4 to 5 orders of magnitude  between the two.)

For what it is worth, do you know which calorie is supposed to be used for the PPE spec?

Mike

the conversion between Joules and calories is not linear with temperature.

No, it isn't, but the effect is frankly piddly, the various calories are named after the temperature of the test.

The most common “15° calorie” (also called the gram-calorie, or small calorie) was defined back when the UK recognised such units as the amount of heat that will raise the temperature of 1 gram of water from 14.5° to 15.5°C—equal to 4.1855 joules. Other less common definitions in this series were the 20° calorie (4.18190 joules) from 19.5° to 20.5° C; and the “mean calorie” (4.19002 joules) defined as 1/100 of the heat necessary to raise the temperature of 1 gram of water from 0° to 100°C.

For nearly all practical purposes, the heat capacity of water is constant, and the conversion factor is approx 4.2 joules per calorie. This applies at all common temperatures used to define the calorie.

Then to confuse matters, dieticians use the word “calorie” for kilocalorie, and are therefore  1000 times higher.  (a Mars bar and a small stick of dynamite are both  about 1 megajoule, so something like 230 diet calories, and 230 000 real ones… by the way  it is really important to note that the rate of energy release during combustion differs by about 4 to 5 orders of magnitude  between the two.)

For what it is worth, do you know which calorie is supposed to be used for the PPE spec?

Mike