Which of the following is one of the four ways to treat and control noise sources?

• A. insulation, sealing, grounding, lighting
• B. training, scheduling, supervision, rewards
• C. drainage, ventilation, filtration, purification
• D. modification, retrofit, substitution and relocation

Answer: (D)

Treating noise at the source means taking engineering actions that directly reduce how much noise a machine or process produces. The best option here covers four practical ways to achieve that: modify the equipment or process to emit less sound, retrofit with noise-reducing components without replacing the whole setup, substitute a quieter material or method in place of a louder one, and relocate the noise source away from workers to reduce exposure. These approaches directly cut the noise where it originates, which is why they are the primary ways to control noise at the source.

Other options point to strategies that don’t change the noise level at the source itself. Insulation, sealing, grounding, and lighting don’t directly lower emitted noise. Training, scheduling, supervision, and rewards adjust human factors or workflows rather than the sound produced. Drainage, ventilation, filtration, and purification relate to environmental or process conditions rather than reducing the noise produced by the source.