Final answer:
The safest method for a firefighter climbing a ladder with a tool in one hand is to slide the free hand along the underside of the beam for balance and security, ensuring a safe ascent and descent.
Step-by-step explanation:
When a fire fighter who is climbing a ladder and carrying a tool in one hand, they should engage in the safest and most secure method of climbing to ensure their own safety and efficiency during fire rescue operations. Option C, to slide the free hand up the underside of the beam while making the climb, is the most appropriate action in this scenario. This technique allows the firefighter to maintain a secure grip on the ladder, providing stability and balance while allowing the other hand to be used for holding tools or equipment. It is important to keep the ladder climb safe, as climbing with only one hand on the rungs, as suggested in Option D, could lead to falls and injuries. Therefore, adhering to safe practices is imperative in emergency situations.