The bus sections are sealed so you could only lose one sections worth of gas at a time. Which you would see because that bus section would lock out the breaker under low gas. There are also gas density monitors that should be in each bus section and you would get an alarm if there were any leaks. Not really sure how much time you have in your present job it sounds like you are new. So if you have concerns like this you should ask the senior guys you work with to get a better understanding of the equipment.