Test the atmosphere.
Keep the decision clear.

Instrument and test-gas assumptions

The G-series monitor, vault, gases and records are fictional. The supplied example challenge is O₂ 18.0%, combustible channel 50% LEL, CO 100 ppm and H₂S 25 ppm. A compatible regulator, adapter and tubing are assumed. Check the gas identity, concentration and expiry. The alternative cylinder is expired and cannot support an accepted check.

A bump test verifies sensor response and the simulated audible, visual and vibration alarm chain. The quantitative CHECK compares the readings with the known gas. The fictional acceptance tolerance is ±0.5 oxygen percentage points and ±10% of the reference concentration for the other channels. SPAN adjusts this fictional instrument; recheck response and accuracy afterward. These settings, tolerances and this combined exercise sequence are teaching choices, not universal manufacturer requirements. A failed alarm chain requires removal from service and a suitable replacement; calibration alone does not repair it.

Remote sampling plan

Remain outside the unoccupied vault. Three specified points in this fictional geometry are top (0.3 m), middle (0.9 m) and bottom (1.8 m). They demonstrate spatial differences; they are not a universal sufficient sampling plan or fixed density map. Real evaluations may require additional contaminants, locations, directions, intervals and conditions.

The fictional 15-second stabilization period includes 7 seconds of line transport and 8 seconds of sensor response. The training clock advances five simulated seconds per real second, or by the manual advance button. Use actual manufacturer timing, line/material suitability, flow checks and the site sampling plan in real work. Review oxygen, then combustible gases, then toxics; the monitor displays all four channels and alarms concurrently.

Exercise action settings

The model flags O₂ below 19.5% or above 23.5%, combustible readings at or above 10% LEL, CO at or above 25 ppm, and H₂S at or above 5 ppm. These are this exercise’s action settings. CO/H₂S settings are not presented as universal OSHA limits or interchangeable with TWA, STEL, ceiling or IDLH values. %LEL is a fraction of a combustible gas’s lower explosive limit, not percent gas by volume. The oxygen range and combustible flag alone do not prove an atmosphere is acceptable.

A four-gas instrument only addresses its supported targets and limitations. Sensor technology, oxygen dependence, calibration gas, cross-sensitivity, poisoning, sample-line effects and unmeasured hazards require proper evaluation. Do not zero an instrument in an unknown atmosphere. Alarm acknowledgment does not remove the hazard. No unplanned entry rescue is practiced here.

• OSHA · Calibrating and Testing Direct-Reading Monitors
• OSHA · Procedures for Atmospheric Testing
• 29 CFR 1910.146 · General industry
• 29 CFR 1926.1204 · Construction
• OSHA atmospheric-testing fact sheet

Source check: October 26, 2026. AI-assisted development. Independent technical, accessibility and learning validation remain pending. Real manufacturer, employer and jurisdictional requirements govern actual work. No agency or equipment-manufacturer endorsement is claimed.