Which of the following is NOT a principal hazard of hydraulics compared to pneumatics?

The principal hazards associated with hydraulics involve the unique characteristics of hydraulic systems, particularly their operation at high pressures. Hydraulics typically operate at much higher pressures than pneumatics, which can lead to dangers such as fluid leaks or bursts resulting in injury or equipment damage.

When considering the options, electrical conductivity is another significant aspect, as hydraulic fluids can be conductive and pose risks related to electrical hazards, especially in systems involving electrical components. Fire risks are also more pronounced in hydraulic systems, particularly due to the nature of hydraulic fluid being flammable and capable of contributing to fire spread.

Noise is relevant in both hydraulic and pneumatic systems; however, it is not inherently a principal hazard of hydraulics compared to pneumatics. While hydraulic systems can generate noise, the level and impact of noise are not significant distinguishing factors when comparing the hazards of hydraulics to pneumatics. Thus, noise does not register as a principal hazard linked specifically to the characteristics of hydraulic systems.