Journeyman Lineman (JL) Verbal Practice Test

In confined-space work, the first thing to verify before entry is the oxygen level in the air. An O2 tester directly measures the percentage of oxygen in the atmosphere, letting you know if there’s enough breathable air (and if ventilation is needed) before anyone goes inside. Keeping this instrument ready ensures you have an immediate, reliable reading to base the entry decision on. The other devices don’t serve that initial atmospheric check as effectively. A thermocouple measures temperature, not air quality. An infrared camera looks for heat and can help spot issues, but it doesn’t quantify gas concentrations in the air. A gas detector badge is worn to monitor exposure during work, but it isn’t used to perform the pre-entry air-quality measurement itself. So, the O2 tester is the best choice for testing air quality and gases before entering the vault.