Which of the following is NOT one of the three types of engineering controls?

The selection of training employees on noise hazards as the correct answer highlights an important distinction between types of noise control measures. Engineering controls are designed to eliminate or reduce hazards at the source, thereby minimizing the risk to workers.

The other options encompass various forms of engineering controls. Regular maintenance of equipment contributes to ensuring that machines operate within safe noise levels and do not emit excess noise due to wear or malfunction. Quieter equipment refers to the use of machinery designed to operate at lower noise levels, directly aiming to reduce noise exposure in the workplace. Enclosing the noise source involves physically isolating the source of noise to minimize its impact on workers, a direct application of engineering principles.

In contrast, training employees, while essential for informing them about the risks associated with noise exposure and promoting safe practices, falls under administrative controls rather than engineering controls. Administrative controls focus on changing how work is done and educating workers, rather than altering the physical workplace or machines directly to reduce hazards. Thus, it is correct to identify training employees on noise hazards as not being an engineering control.