What is the proper sequence for testing atmospheres in confined spaces?

The proper sequence for testing atmospheres in confined spaces starts with measuring the oxygen content, followed by assessing combustible gases, and finally checking for toxic gases. This sequence is crucial for maintaining safety in confined space operations.

First, determining the oxygen content is vital because a safe oxygen level (between 19.5% and 23.5% by volume) is necessary for worker safety. If the oxygen level is too low or too high, it can pose immediate health risks, making it the first parameter to check.

Next, evaluating combustible gases is important because their presence can lead to explosive conditions if they exceed the lower explosive limit (LEL). Identifying combustible gases after confirming that an adequate oxygen level exists helps ensure that any potential ignition sources are diminished.

Lastly, testing for toxic gases is vital but should occur after confirming that the atmosphere is safe regarding oxygen and combustibles. This sequential approach helps establish a safer work environment, allowing for timely identification of hazards and appropriate measures to mitigate risks actively.

The other sequences, while they may seem reasonable, do not prioritize safety in the best way for confined space entry.