Final answer:
The most important safety consideration when connecting a nitrogen cylinder to a system is managing the pressure within the cylinder, especially in response to temperature changes that can significantly increase pressure and pose risks.
Step-by-step explanation:
When a dry nitrogen cylinder from a portable cylinder is connected to a system, the item of most importance in consideration of safety is the pressure within the cylinder. Gas cylinders are stored under high pressure, and if a cylinder is exposed to heat, such as from a fire, the pressure inside can increase significantly, posing a risk of explosion. Thus, it's critical to ensure that the cylinder's pressure does not exceed its safety limits, adhering to safety protocols to prevent accidents.
Example scenarios demonstrate the importance of managing temperature to control the pressure in a cylinder. When a high-pressure gas cylinder valve leaks, for instance, cooling the cylinder to dry ice temperature can effectively reduce both the leak rate and the internal pressure, allowing for safe repairs to be made. However, this process should be approached with caution, taking into account the potential risks and ensuring that the cylinder's integrity is not compromised during the temperature and pressure adjustments.