Certified Hyperbaric Technologist Practice Test

During the filling of a scuba tank at room temperature, the tank will get warmer. What effect does this have on the pressure of the gas in the cylinder?

1. The pressure will increase

2. The pressure will decrease

3. The pressure will remain constant

4. The pressure will fluctuate

The correct answer is: The pressure will decrease

When a scuba tank is filled with gas at room temperature, the warming of the gas occurs primarily due to the compression that takes place as the tank is filled. According to the ideal gas law, if the volume of a gas is held constant and its temperature increases, the pressure also tends to increase. However, it's important to differentiate between the transient state of filling and the long-term conditions once the tank is sealed and the temperature stabilizes. During the filling process, the gas does heat up due to compression, which can initially raise the pressure momentarily; however, once the tank is sealed and the temperature begins to equilibrate with the environment, the constant cooling will lead to a decrease in pressure over time. Additionally, if the tank is left to stand after filling, it will reach thermal equilibrium with the surrounding environment, leading to a pressure decrease due to temperature equalization. Thus, the pressure in the scuba tank can decrease as the gas cools after it has been compressed and filled at room temperature, emphasizing that while filling can create a transient increase due to temperature rise and compression, the longer-term effect includes the cooling of the gas leading to lower pressure. This aligns with the principles of thermodynamics and fluid dynamics as applied to gas behavior in