Final answer:
Readings must indicate that oxygen levels are between 19.5% and 23.5%, and contaminants are below permissible limits before removing SCBA. Toxic gases must also be absent or within acceptable ranges. These safety assessments are made using air monitoring equipment.
Step-by-step explanation:
To determine when it is safe to remove SCBA (Self-Contained Breathing Apparatus), specific readings are required. SCBA is utilized in environments that are considered to be Immediately Dangerous to Life or Health (IDLH). Safety protocols generally dictate that a user should not remove their SCBA until the air quality is deemed safe, which typically means that the environment must have an oxygen level between 19.5% and 23.5%, and contaminants must be below their respective permissible exposure limits (PELs) or Threshold Limit Values (TLVs).
Moreover, toxic gases such as carbon monoxide and hydrogen sulfide need to be absent, or at levels that fall within acceptable limits. These readings are taken using various gas detectors and air monitoring equipment. It is critical for the safety of the user that these conditions are firmly established before SCBA removal to prevent exposure to harmful atmospheres.