🔍 Key Concepts

• This is a combustible gas indicator/explosimeter used to test a space for flammable gases before entry • Think about what can change when an instrument sits unused for several weeks (power source, internal air, calibration/zero) • Each step listed in the choices affects safety and accuracy of the reading in a potentially explosive atmosphere

💭 Think About

• For each option (purging, zeroing, checking batteries), ask yourself: what problem does this prevent when checking a confined or poorly ventilated space? • Which of these actions would you normally perform as part of a pre‑use check on any portable gas‑measuring instrument, especially after long storage? • Does skipping any one of these steps create a risk of either a false safe reading or the instrument failing when you need it most?

✅ Before You Answer

• Consider the role of the batteries in driving the meter movement and the catalytic filament shown in the illustration • Look at the zero adjust control and the meter scale – what must be true about the pointer before you can trust any reading? • Think about the sampling hose and internal passages: after weeks of disuse, why might you need to move several bulbfuls of fresh air through the system before taking a reading?