Portable gas detectors use two main sampling methods: diffusion and pump. The difference seems simple, but it has a direct impact on safety, response time, and how confidently you can test a space before entry.
Choosing the wrong sampling method is a common mistake, especially for sites that do a mix of open area checks and confined space entry. Use the comparison below to choose the method that matches your most dangerous task.
How diffusion sampling works
Diffusion detectors rely on natural air movement. Gas molecules travel into the sensor by ambient airflow. This design is lightweight, low maintenance, and energy efficient. For routine patrols, general inspections, and personal monitoring, diffusion is often the simplest choice.
- Best for open areas with good airflow
- Lower maintenance because there is no pump to service
- Longer battery life because power use is lower
Where diffusion can fall short
Diffusion sampling cannot reach into a space that you are not physically in. If you need to sample a tank, manhole, pit, or vault before entry, diffusion alone is not enough. Still air can also slow response time, which matters when gas levels are changing quickly.
How pumped sampling works
A pumped detector actively draws air through tubing. This lets you test a space from a safe distance and sample multiple heights. Pumped sampling is the standard for confined space pre-entry checks because it allows you to verify the atmosphere without exposing a worker.
- Best for confined spaces and unknown atmospheres
- Faster response in still air
- Allows sampling at different depths or layers
Trade-offs to consider
Pumped detectors cost more, require more maintenance, and can reduce battery life. Tubing can clog, filters need replacement, and pumps can fail if exposed to moisture or dust. That is why many teams use diffusion for daily work and reserve pump sampling for high-risk tasks.
Response time and sampling depth
Gas behavior changes by type. Methane tends to rise while heavier vapors can settle near the floor. With a pump, you can sample multiple levels before entry. With diffusion, you must physically move to each level, which is not possible if the space is unsafe to enter.
- Sample top, middle, and bottom in confined spaces
- Pause at each level to let the sensor stabilize
- Keep tubing clear and avoid kinks or moisture traps
Maintenance and failure modes
Diffusion units are simple, but they still need care. Keep sensor inlets clean and avoid blocking the diffusion path. Pumped units add more failure points, so include these checks in your routine:
- Inspect filters and tubing for dust or liquid
- Verify the pump flow rate during bump testing
- Replace worn tubing before it cracks or collapses
Policy, training, and cost
Sampling method should be built into your permit process and training. If the job requires pre-entry testing, a pump is not optional. If the job is open area patrols, a diffusion unit may be more cost effective and easier for crews to manage. Define this in your procedures so teams do not guess in the field.
Quick decision checklist
- Do you test confined spaces before entry? If yes, use a pump.
- Is the work mostly in open areas? Diffusion may be enough.
- Do you need flexibility? Consider a diffusion unit with an optional pump.
Product spotlight: flexible sampling with optional pump support
Some diffusion detectors allow a handheld external pump for pre-entry checks. The BTYQ-GS4 multi-gas detector uses diffusion sampling and supports an optional external pump, which gives crews a flexible approach without carrying a pump on every routine patrol. It also provides sound, light, and vibration alarms and is built with IP67 protection for harsh field conditions.
This type of flexibility is valuable when your daily work is mixed and you need both speed and safety.
Final takeaway
Diffusion is simple and efficient for open areas. Pumped sampling is the safest method for confined spaces and unknown atmospheres. Pick the method that matches your highest risk task and then train to that method. A detector is only as safe as the sampling strategy behind it.