Which factor is NOT considered a risk for fire hose damage?

High humidity is indeed not typically considered a direct risk for fire hose damage compared to the other factors listed. Mildew can develop in damp conditions, particularly on hoses that are not dried properly, leading to deterioration of the material. Mechanical stress refers to the physical strain placed on hoses during use or handling, which can cause abrasions or tears. Cold temperatures can lead to brittleness in certain materials, making hoses more susceptible to cracks or other forms of damage. Therefore, while high humidity can affect the overall environment, it is not as direct a threat to the physical integrity of fire hoses as the other factors mentioned.