Pump-Aspirated Confined Space Gas Monitor — Training Guide

A four-gas monitor that draws its sample down a hose. Everything that makes this instrument different from a clip-on diffusion detector comes from that one fact.

1. Display requirements

Minimum 980 × 600 px. Recommended 1920 × 1080 (16:9) or larger. Below the minimum the simulator shows a "Screen Too Small" notice instead of running.

2. Why an aspirated instrument needs its own training

A diffusion detector sits in the atmosphere it measures. An aspirated instrument does not — it stands at the manhole while a pump pulls the atmosphere up a hose to it. Three consequences, and they are the whole syllabus:

1. The reading arrives late. The delay is the hose volume divided by the pump flow. It is not a quirk to be tolerated; it is a number you must know before you believe a display.
2. A space is not one atmosphere. Combustible gas is usually lighter than air and gathers at the top. Hydrogen sulfide is heavier and settles at the bottom, where oxygen has also been eaten by corrosion. A reading at the manhole describes the manhole.
3. A frozen reading looks like a safe reading. When flow fails, the number simply stops changing — and a number that is not moving is very easy to trust.

3. The instrument

3.1 Channels, ranges and alarm points

Oxygen is the exception to every rule here: its first alarm is a LOW alarm and its second is a HIGH alarm, because both depletion and enrichment are hazards.

3.2 The four switches

3.3 The display

Four quadrants — combustible and oxygen on the top row, carbon monoxide and hydrogen sulfide beneath — each with a value and a bar graph. The status strip carries a pilot indicator that blinks while detecting, a pump indicator that turns only while gas is genuinely moving, the battery icon and the clock. In an alarm the affected value blinks; over-range shows ∩∩∩ and a failed sensor shows ---. Neither is ever a number you can act on.

3.4 The display / setting menu

DISPLAY opens it; ▲/▼ step through PEAK, STEL, TWA, ALARM-P, PUMP and ID. PEAK holds the highest reading seen since power-on — except oxygen, where it holds the lowest. PUMP with ENTER stops and starts the suction.

4. The transit delay — the central skill

The left panel computes it live:

transit (s) = hose length (m) × hose volume per metre (mL/m) ÷ pump flow (mL/s)

With a 0.75 L/min pump and a typical sampling hose that is roughly 1.4 seconds for every metre. A 20 m hose is close to 30 seconds before the atmosphere at the probe even reaches the sensor — and then the sensor still needs its own T90 on top.

The SAMPLE LINE bar above the instrument fills as the column is exchanged. While it is amber you are looking at hose air. When it turns green the reading represents the probe.

5. Procedure

5.1 Before switching on

• Battery level sufficient.
• No bend, split or blockage in the sampling hose. A split hose draws room air in and dilutes everything — the classic false "safe" reading.
• Probe filter clean and free of dust.
• Probe and hose connected to the GAS IN port and locked.

5.2 Switching on

Hold POWER for three seconds. The instrument lights every segment, then walks its date/time, battery, gas names, full scales, first and second alarm points, STEL, TWA and ID before entering detection mode. Watch that scroll — it is how you confirm the setpoints are what you expect.

5.3 Fresh air adjustment

In genuinely clean air, hold AIR. The instrument purges, then zeroes the combustible and toxic channels and sets oxygen to 20.9 vol%.

5.4 Surveying the space

1. Note the hose length and the transit time it implies.
2. Lower the probe to the top of the space. Wait for the sample line bar to fill. Log the level.
3. Repeat at the middle, then the bottom, waiting the full transit each time.
4. Judge entry on the worst reading at any level, not the average and not the first.

5.5 Alarms and reset

Gas alarms latch. Once a setpoint is reached the alarm stays up even after the gas clears. RESET clears it only when the reading has genuinely returned below the setpoint — pressing it while still in the gas is refused, and the simulator tells you so. TWA and STEL alarms never reset: the exposure has already happened.

Fault alarms auto-recover once the cause is gone, except the flow fault, which needs the restriction removed and then a deliberate RESET.

6. Training scenarios

Routine pre-entry survey beginner

Objective: complete the pre-start checks, adjust in fresh air, survey all three levels waiting the full transit each time. Expected result: all four channels within limits at every level; entry may be declared safe. Pass: 70. Par: 12 min.

Stratified space intermediate

Objective: recognise that the manhole reading does not describe the space. Oxygen falls from 20.9 vol% at the top to 13.4 vol% at the bottom and H2S rises to 38 ppm. Expected result: the top reads clean; only a bottom sample finds the hazard. The correct answer is to refuse entry. Pass: 80. Par: 15 min.

Combustible layer under the deckhead intermediate

Objective: the mirror image — 62 %LEL at the top falling to zero at the bottom. A trainee who tests only the bilge declares a flammable space safe. Observe both alarm steps and practise resetting the latch only after withdrawing. Pass: 80. Par: 12 min.

Flow failure during a survey advanced

Objective: the probe filter is clogged from the start. Suction falls below threshold, FAIL LOW FLOW raises and the reading stops tracking the probe. Expected result: notice the fault, treat the reading as void, clear the filter from the pre-start checks panel, press RESET, and re-sample. Pass: 80. Par: 10 min.

7. Instructor controls

Ctrl+Shift+F opens the fault panel. Available faults: clogged probe filter, split hose, degraded pump, H2S sensor failure, CO zero drift (+18 ppm) and low battery. Each produces a realistic consequence rather than a binary break — the split hose, for example, dilutes the sample toward clean air rather than simply stopping it.

8. Keyboard shortcuts

9. Scoring

Start at 100.

Grades: A 90+, B 75–89, C 60–74, D below 60.

10. Troubleshooting