Choosing an open path gas detector starts with a practical question: where could a hazardous gas cloud travel before the site needs to respond? Point infrared detectors measure gas at individual locations, while open-path infrared systems monitor gas along a beam. Both may be evaluated for industrial gas monitoring, but they provide different information. For procurement teams comparing coverage and cost, the useful starting point is the release scenario, site geometry and required response, followed by equipment selection.
How Open-Path and Point Infrared Detection Differ
Infrared gas detection uses the absorption of infrared light by a target gas. A point detector measures gas entering its local sensing area. Its reading describes conditions at that location, so a release must reach the detector before it can be detected. A well-positioned point device can support monitoring near an identified leak source, but it does not measure every space around it.
An open-path system separates the optical transmitter and receiver across a monitored route. Gas intersecting the beam contributes to its reading. This creates a line of detection rather than a measurement at one position. Honeywell describes this arrangement in its overview of open-path monitoring. A cloud that travels above, below or beside the beam may remain undetected.
The measurement units also matter. Point flammable-gas instruments commonly report a percentage of the lower explosive limit, or %LEL. Open-path instruments commonly report a path-integrated value, such as LEL.m, representing concentration accumulated along the beam. As explained in Honeywell’s gas detection reference guide, this differs from a concentration at a single point. The same path-integrated reading can arise from different cloud concentrations and lengths, so it cannot identify the peak concentration without additional information.
Coverage Depends on Layout and Release Scenarios
For point detection, engineers consider likely leak sources, ventilation, obstructions and the routes by which gas may reach each sensor. Equipment enclosures and congested process areas may favor individual monitoring positions. However, increasing the number of detectors does not automatically resolve poor placement. Access for inspection and functional testing also needs to be part of the layout.
Open-path detection may be evaluated for open process areas or routes across which a drifting cloud could pass. The beam requires a suitable optical route and stable mounting positions. Vehicle movements, temporary scaffolding, stored materials and later plant modifications can interfere with that route. A clear line on a drawing needs to remain usable during normal operations and maintenance.
Environmental conditions deserve specific attention. Fog, airborne dust, steam, rain and contaminated optical surfaces can affect optical signal availability, depending on the equipment and circumstances. Buyers should ask how the proposed system identifies reduced signal or beam blockage and how operators distinguish these conditions from gas alarms. A fault indication needs an agreed operational response; it should not be treated as evidence that the area is gas-free.
Some facilities may benefit from a combined arrangement: point detectors near selected sources and open-path monitoring across credible cloud travel routes. This is a design option to evaluate through the site risk assessment, rather than a universal requirement. ASA’s industrial monitoring applications provide a starting point for discussing the intended operating environment.
Compare Installed and Lifecycle Costs
Purchase price alone gives an incomplete comparison. A point detection proposal may involve several mounting locations, cable routes, power connections and controller inputs. An open-path proposal may involve fewer monitored routes but require dedicated supports, alignment work and access at separated optical units. Neither arrangement is inherently the lower-cost choice for every facility.
Ask bidders to quote against the same monitoring objectives and operating assumptions. A proposal covering one open corridor cannot be compared directly with a proposal monitoring multiple enclosed leak sources. Where coverage differs, the commercial comparison should identify those differences before procurement evaluates the total price.
- Installation: mounting structures, cabling, power provision, access equipment and commissioning labor.
- Integration: signal compatibility, alarm and fault handling, operator displays and documented response logic.
- Maintenance: cleaning, functional checks, alignment verification where applicable, spare parts and service access.
- Operational support: maintenance records, staff training and arrangements for periods when monitoring is unavailable.
For European and Middle Eastern projects, the specification should describe actual site conditions, including temperature variation, dust exposure, moisture and maintenance access. Regional labels are too broad to define an instrument’s suitability. Request documented environmental limits and a maintenance approach for the proposed model, without assuming that a general technology description establishes product capability.
Match the Technology to the Use Case
Point infrared detection can be considered where the objective is to monitor gas at defined locations around equipment or inside a suitable enclosure. Open-path detection may be evaluated where an unobstructed route can intercept a relevant gas cloud. Congested layouts, changing storage arrangements or frequent beam interruptions may make an open-path arrangement difficult to maintain in service.
Gas compatibility must be confirmed separately from coverage. Infrared detection is not suitable for every gas, and a detector configured for one target should not be assumed to measure all combustible gases correctly. Specify the expected substances or mixtures and request the manufacturer’s documented response information. Do not infer sensing technology from a product name or from a general gas detector category.
Before placing an order, define what each alarm and fault will trigger, who will investigate and how equipment will be checked after maintenance. Detection is one input to a wider safety strategy. The selected arrangement should be reviewed alongside ventilation, operating procedures and other protective measures by personnel responsible for the site’s risk assessment.
Why ASA
ASA’s product scope includes gas detectors, dust alarm detectors and gas alarm controllers, giving buyers several monitoring categories to discuss during project planning. The gas alarm detector range is a starting point for product inquiries. Availability of a particular infrared or open-path configuration should be confirmed directly.
To support an engineering discussion, share the target gas, site layout, monitoring objective and controller interface requirements. Include the project schedule so that documentation and response expectations can be agreed early. Contact ASA to discuss your monitoring requirements and request model-specific information before selection.
Disclaimer: Product availability, specifications, measuring ranges, alarm configurations and certification coverage vary by model and region. The information in this article is provided for general reference only and does not constitute a performance guarantee, safety assurance or compliance statement. Always refer to the official product documentation and confirm suitability, certification status and local regulatory requirements with our team before selection, installation or use.
