Final answer:
WAH certificate and fixed fall protection system are used for work conducted at a height greater than a certain threshold to ensure safety.
Step-by-step explanation:
WAH certificate (Work at Height certificate) and fixed fall protection system should be used for work that is conducted at a height greater than a certain threshold to ensure safety.
For example, in the construction industry, a WAH certificate may be required for workers who perform tasks at a height above 2 meters. Similarly, a fixed fall protection system, such as guardrails, safety nets, or personal fall arrest systems, should be in place for work conducted at a certain elevation to prevent falls.