Final answer:
Using oxygen or compressed air to pressurize a system is dangerous due to the risk of explosions, potential system damage, increased likelihood of leaks, and potential contamination of the system.
Step-by-step explanation:
You should never use oxygen or compressed air to pressurize a system primarily because it can cause an explosion. Oxygen is a highly reactive gas that can greatly enhance combustion, leading to explosive reactions when combined with flammable materials. Similarly, when any gas is compressed, it stores potential energy that can be released in an explosive manner if the container fails.
Additionally, using compressed oxygen or air can damage the system by exerting excessive pressure, which can exceed the designed tolerances of the system components. Such over-pressurization can also lead to leaks due to the strain put on the seals and joints. Lastly, using compressed air could introduce moisture or oil from the compressor, which could contaminate the system, especially if it's a system that requires high purity gas, such as in medical or laboratory settings.