Not sure which gas detector to choose? This guide covers everything you need. Selecting the right gas detector comes down to three criteria: ① Sampling method (pump-draw vs. diffusion), ② Number of target gases (single vs. multi-gas), and ③ Installation type (portable vs. fixed). Each criterion is explained with real-world examples.
1. Pump-Draw vs. Diffusion: How Is the Air Sample Collected?
Gas detectors use two main sampling methods. The key deciding factor is whether you can physically enter the measurement area.
Pump-Draw Type (Forced Suction)
An internal electric pump actively draws air from a remote location into the sensor. With a sampling tube (hose) attached, operators can check gas concentrations several to tens of meters away without entering hazardous areas.
📌 Pump-Draw Field Examples
Pre-entry inspection of confined spaces (manholes, tanks, underground pits) / Remote detection at suspected pipeline leak points / Measuring areas with difficult direct access such as ceilings or floors
Diffusion Type (Natural Diffusion)
Without a pump, the sensor naturally contacts the surrounding air to measure concentration. Simple in structure with low battery consumption, it is optimal for workers to monitor their real-time exposure while working in the area.
📌 Diffusion Type Field Examples
Personal protection clipped to waist or chest / Continuous monitoring in open workplaces / Environmental surveillance in large spaces
| Category | Pump-Draw | Diffusion |
|---|---|---|
| Sampling method | Forced suction via electric pump | Natural diffusion |
| Remote measurement | Yes (with hose) | No (must be worn on-site) |
| Battery consumption | High | Low |
| Primary use | Pre-entry inspection of confined spaces | Personal worker protection |
| Response speed | Fast (active suction) | Relatively slower |
2. Single-Gas vs. Multi-Gas Detector: How Many Gases Need to Be Detected?
The choice depends on how many types of gases must be measured. Multi-gas detectors are better for complex environments, while single-gas detectors are more economical and accurate when only one gas is present.
Single-Gas Detector
Designed to detect only one specific gas. Optimized for that one sensor type, offering high measurement precision at a lower price. Ideal for environments where the hazardous gas is clearly identified.
📌 Single-Gas Detector Field Examples
Dedicated natural gas (CH₄) pipeline inspection / Ammonia (NH₃) leak monitoring in cold-storage warehouses / Parking garages or boiler rooms where CO is the sole expected hazard
Multi-Gas Detector
Simultaneously detects 2–5 or more gases. Essential for confined spaces and complex hazard environments where oxygen (O₂) deficiency, combustible gas (LEL), carbon monoxide (CO), and hydrogen sulfide (H₂S) must all be monitored with one device. The WANDI EDW500 series allows flexible sensor combinations — electrochemical (EC), catalytic bead, PID, and IR — tailored to site requirements.
📌 Multi-Gas Detector Field Examples
Sewer/manhole work (simultaneous O₂+CO+H₂S+LEL monitoring) / Petroleum and petrochemical plants / Shipyard painting and welding zones / Sites with mixed gas hazards
| Category | Single-Gas | Multi-Gas |
|---|---|---|
| Gases detected | 1 type | 2–5+ types |
| Price | Lower | Relatively higher |
| Precision | Optimized for one gas | Balanced across multiple gases |
| Suitable environment | Single gas hazard environment | Confined spaces / complex hazard environments |
| Legal requirements | Specific gas monitoring | Required for confined space entry |
3. Portable vs. Fixed: Will It Move with the Worker or Stay in One Place?
Usage pattern determines whether you need a portable or fixed detector. These two types are complementary rather than competing — many facilities operate both.
Portable Gas Detector
Battery-powered and carried by workers or used for mobile inspections. Ideal for pre-entry measurements in confined spaces, patrol/inspection duties, and emergency leak response. The WANDI EDW500 is an IECEx and KC explosion-proof certified portable multi-gas detector, safe to use even in Zone 0 (the highest hazard classification).
📌 Portable Detector Field Examples
O₂ and hazardous gas pre-check before entering manholes/tanks / Gas pipeline patrol inspections / Real-time monitoring during emergency response team deployment
Fixed Gas Detector
Permanently installed at a specific location for 24-hour continuous monitoring of gas concentration at that point. Can be integrated with central control rooms to trigger alarms and automatically activate ventilation fans or shutoff valves.
📌 Fixed Detector Field Examples
Continuous LNG storage tank perimeter monitoring / Special gas leak detection in semiconductor fabs / Automatic ventilation control linked to CO levels in large parking structures / Continuous boiler room and machine room monitoring
| Category | Portable | Fixed |
|---|---|---|
| Power source | Battery (rechargeable) | Mains power (AC/DC) |
| Monitoring method | Mobile on-site inspection | Continuous surveillance at fixed point |
| System integration | Typically standalone | DCS/PLC/alarm system integration |
| Installation cost | Low | High (includes wiring and installation) |
| Primary use | Confined space entry and patrol inspection | Plant/facility continuous safety management |
4. Situation-Based Selection Checklist: Choose in 3 Steps
- 1Can you physically enter the measurement area?
Cannot enter → Pump-draw type / Can be worn or stationed there → Diffusion type - 2Is the type of gas clearly identified?
Only one gas → Single-gas detector / Multiple types or confined space → Multi-gas detector - 3Will you move around with it or keep it in one place?
Mobile inspection → Portable / 24-hour continuous monitoring → Fixed
5. Recommended Combinations by Site Type
| Site Type | Recommended Configuration | Reason |
|---|---|---|
| Sewer/manhole work | Pump-draw + Multi-gas + Portable | Remote pre-entry measurement, simultaneous O₂/H₂S/CO/LEL detection required |
| Natural gas pipeline patrol | Pump-draw or Diffusion + Single (CH₄) + Portable | Methane-only detection for mobile inspection |
| Petrochemical plant | Diffusion + Multi-gas + Portable (personal) + Fixed (facility) | Combined personal worker protection and continuous facility monitoring |
| Semiconductor/display factory | Fixed + Single (per process gas) | Fixed monitoring by process-specific gas type with DCS integration |
| Large parking structure | Fixed + Single (CO) + Diffusion | Automatic ventilation fan activation based on CO concentration |
💡 About the WANDI EDW500 Series
The WANDI EDW500 is a portable multi-gas detector with IECEx and KC explosion-proof certification. It supports flexible sensor combinations — electrochemical (EC), catalytic bead (CAT), PID, and IR — tailored to site requirements, and is safe for use even in Zone 0 (the highest hazard level). A trusted choice backed by major domestic and international certifications.
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📖 5-Gas Detector Complete Guide 2026
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📖 Korean OSH 5-Gas Mandatory Requirements
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📖 Confined Space Safety Procedures Guide
Essential pre-entry checks for septic tanks and manholes