- In the management of hazardous substances, the hierarchy of controls is a fundamental concept used to minimize exposure and ensure safety.
- This hierarchy prioritizes control methods starting with the most effective and reliable approaches.

- The most effective control measures are elimination and substitution, where the hazard is completely removed or replaced.
- When this is not possible, engineering controls (such as ventilation systems, containment, and isolation) are implemented to physically remove or reduce the hazard from the workplace environment.

- Only when engineering controls are inadequate or cannot fully protect employees, do we resort to personal protective equipment (PPE) like respirators.
- PPE is considered a last line of defense because it relies on proper use and maintenance, and does not eliminate the hazard itself.

Therefore, the use of respirators is appropriate only when engineering controls are inadequate. It is not correct to use them exclusively after administrative controls fail or when PPE alone is sufficient. Also, respirators are not used after complete elimination of the hazard since the risk no longer exists.

Key points:
- Hierarchy of controls prioritizes elimination and engineering controls over PPE.
- Respirators are used as a last resort when engineering controls are insufficient.
- Reliance solely on PPE is less effective than engineering solutions.
- Complete elimination of hazard negates the need for respirators.

Reference: Occupational Safety and Health Administration (OSHA) Guidelines, Volume II, Chapter 6 - Respiratory Protection