Safe handling and storage practices for emergency oxygen systems include:

Carrying unprotected oxygen cylinders with two hands is the correct practice because it ensures better control and reduces the risk of dropping the cylinder, which could lead to an accident or injury. Using two hands allows for a secure grip and stability, which is essential since oxygen cylinders can be heavy and awkward to maneuver.

In contrast, the other options highlight unsafe practices. Storing cylinders in excess heat can cause increased pressure inside the cylinder, which may lead to a rupture or explosion. Transporting cylinders in a closed vehicle without ventilation poses a danger if there is a leak, as oxygen can accumulate and create a fire hazard. Keeping oxygen cylinders in a confined space can also restrict proper ventilation, increasing the risk of pressure buildup and other safety issues. Therefore, safe handling and storage practices are crucial for maintaining the safety of emergency oxygen systems.