Forensics 4 Gas Meter vs 4 Gas Monitor with Pump: Which to Buy?
Forensics 4 Gas Meter vs 4 Gas Monitor with Pump?
Short answer: Both are NIST-calibrated O2/LEL/CO/H2S monitors. Choose the 4 Gas Meter (diffusion) for lightweight spot checks; choose the 4 Gas Monitor with Pump when you must sample a space before entry.
The only real difference is sampling method, and it matters a lot for confined-space entry. Both are in Portable Gas Detectors.
At a glance
| Spec | 4 Gas Meter | 4 Gas + Pump |
|---|---|---|
| Gases | O2, CO, H2S, LEL | O2, CO, H2S, LEL |
| Sampling | Diffusion | Motorized pump + probe |
| Pre-entry remote test | No | Yes |
| NIST certificate | Yes | Yes |
| Weight | 4.8 oz | Heavier (pump) |
| Street price | ~$199 | ~$299 |
4 Gas Meter
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4 Gas + Pump
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Which should you buy?
- Choose the 4 Gas Meter for the lightest, lowest-cost diffusion monitor for routine checks.
- Choose the pump version when you must test a tank, vault or manhole before anyone enters.
- See the wider portable lineup and the diffusion vs pump explainer.
Diffusion vs sample-draw
A diffusion meter reads the air around it — fine for spot checks and personal monitoring. A pump draws a remote sample through a probe so you can test the bottom of a confined space from the surface, before entry. If your work involves permit-required confined spaces, the pump is usually worth the extra cost. Both ship NIST-calibrated; bump-test with gas from Calibration & Accessories.
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Frequently asked questions
What is the difference between the two?
Sampling method — the 4 Gas Meter is diffusion (reads ambient air); the pump version draws a remote sample through a probe for pre-entry testing.
Which do I need for confined-space entry?
The pump version lets you test a sealed space before entry; the diffusion meter is for monitoring once it is safe or for spot checks.
Are both NIST calibrated?
Yes — both ship with a USA NIST calibration certificate.
Which is lighter?
The diffusion 4 Gas Meter at 4.8 oz; the pump adds bulk and weight.
Which is cheaper?
The diffusion meter (~$199) versus the pump (~$299).
Do both detect the same gases?
Yes — O2, CO, H2S and combustible LEL.
Does the pump need maintenance?
Yes — keep the pump and probe clean and check flow per the instructions.
Can the diffusion meter ever do pre-entry testing?
Not remotely; it must be in the space. For remote sampling you need the pump.
How often do I calibrate?
Bump-test before each day of use and calibrate on the manufacturer's schedule.
Do they cover VOCs?
No — for VOCs use a VOC detector.
Disclosure & how we compare. WC Safety is an independent industrial safety-equipment retailer. Comparisons are based on manufacturer specifications and intended use, framed against OSHA 29 CFR 1910.146 and OSHA PELs. We participate in the Amazon Associates Program (tag wcsafety04-20) and earn on qualifying purchases; that does not change our recommendations. Buyer guidance only, not medical, legal or regulatory advice.
By Steven Eaton, WC Safety Editorial · · industrial gas-detection desk.