Some recent articles regarding “Deflategate” have suggested that temperature changes between the equipment room and the playing field could explain away the drop in ball pressure. I do not claim to be a scientist, but having worked in industry for over 35 years, including several years with a company that producing industrial gasses (and I once stayed in a Holiday Inn Express) I am quite familiar with the science associated with this issue. Let’s take a look.
When air is pumped into a football it begins to exert pressure against the inner surface of the football. This pressure is generally expressed in pounds per square inch (psi). The minimum pressure allowed by the NFL specification is 12.5 psi. Unfortunately this specification is lacking one key component – temperature. Because gasses expand and contract with temperature changes, it follows that the pressure exerted on the inner surface of the ball would change with temperature as well. This is not something that can happen; it is something that will happen.
Here is the formula used to calculate the change in temperature (note – this formula requires temperatures to be expressed in degrees Kelvin which is accomplished by adding 460 to the temperatures in Fahrenheit).
P2 = P1(T2/T1)
If we assume the balls were inflated in a room at a temperature of 70 degrees F (294 degrees K) to the minimum pressure of 12.5 psi, and were then stored on the playing field where the temperature was around 50 degrees F ( 283 degrees K).
P2 = 12.5(283/294) = 12.03 psi
(Note: edited to correct temperature conversions)
Clearly a 20 degree drop in temperature would not account for a loss of 2 psi. In order for temperature changes to explain that loss, the balls would have to have been inflated at a temperature of over 145 degrees Fahrenheit before cooling to 50 degrees on the sidelines, something that is possible but not likely to happen by accident.
Although we may never know the truth about what happened, the NFL could take steps to prevent this from being an issue in the future.
First, it is customary for a pressure specification to also include a reference temperature. Any pressure tests conducted would reference the pressures to the actual temperature to get an accurate reading.
The other change that I would suggest would be for NFL officials to supply the balls used during the game and both teams would use the same balls, eliminating any chance of one team having an advantage over the other due to an under or over inflated ball.