GasData GFM436

GasData GFM436 is designed as a complete investigation and control tool for ground-gas regimes in brownfield, greenfield and landfill settings. As a fixed-configuration instrument, it provides dedicated methane measurement by both volume and Lower Explosive Limit (LEL), supporting direct safety and risk assessment in boreholes and gas control systems. Simultaneous monitoring of methane, carbon dioxide, oxygen, hydrogen sulphide and carbon monoxide builds a clear picture of gas generation, migration and potential exposure risks across complex sites.

Alongside gas composition, the analyser measures atmospheric, static and dynamic differential gas pressures and offers true bi-directional borehole flow measurement using an internal high-precision thermal mass flow transducer. Optional plug-in temperature and vane anemometer inputs extend this capability to gas temperature and velocity in extraction pipelines and wellhead lines, giving a single platform for assessing both emission from and ingress into boreholes.

For detailed technical data, consult the Specifications tab.

Ground-gas regimes around landfills and historically industrial land often contain mixed hydrocarbons from fuels, oils and other contaminants, which can distort conventional methane measurements. GasData GFM436 addresses this with a dedicated hexane measurement scale based on proprietary non-dispersive infra-red (NDIR) sensors. By referencing against hexane, it differentiates biodegradation-derived methane from other hydrocarbon vapours and avoids erroneous or over-range methane readings where non-methane hydrocarbons are present.

The analyser also provides a PID compensation factor for use alongside separate photo-ionisation detectors. This enables correction of PID readings for methane interference, improving the accuracy of low-level VOC measurements and supporting more reliable characterisation of both natural and anthropogenic contamination sources.

For active gas extraction and control systems, physical behaviour is as important as gas composition. GasData GFM436 measures atmospheric, static and differential pressures and records both instantaneous and peak borehole flows, enabling detailed diagnosis of gas regimes. Its internal thermal mass flow transducer provides true bi-directional measurement, supporting assessment of gas movement into and out of boreholes and extraction infrastructure.

The ability to measure flow while simultaneously indicating precise pressure differences down to a few Pascals helps optimise gas extraction system performance. Static and differential pressure readings support control valve and gas pump balancing, aiding tuning of wellfields and manifold systems and contributing to long-term redevelopment monitoring on land impacted by historic industrial use or adjacent to landfills. Within the GFM family, GFM436 is differentiated by direct measurement of higher flow rates in litres per hour via its internal electrical mass-flow component.

GasData GFM436 is configured for frequent transport and use across multiple boreholes and locations. Its compact, lightweight and robust hand-held format is weather resistant and supplied with a protective leather case for additional durability in demanding field conditions. A high-contrast, bright LCD display with clear screen layouts and intuitive operator buttons supports reliable operation in poor weather and low-light environments.

The standard site kit includes the analyser, a sample pipe with dust-trap filter, charger, spares, tools and a USB manual, providing a ready-to-deploy package with minimal on-site setup. The dust-trap filter protects internal sensors from particulates, helping maintain measurement integrity and extending service life. A user-swappable, field-exchangeable battery pack typically provides approximately 8–12 hours of operation, with a maximum recharge time of around four hours, and instruments are supplied fully charged to enable immediate deployment.

To reduce manual data handling and transcription errors, GasData GFM436 incorporates both manual and unattended (programmable) data-logging modes with a real-time clock for long-term monitoring. SiteMan PC software is included for instrument configuration, sample point labelling, data management and reporting. Data is transferred via USB and exported in CSV and AGS 3.1/4 formats, aligning directly with common geotechnical and environmental reporting workflows and helping eliminate separate spreadsheet entry.

The analyser stores two water-level readings from a dip meter for each borehole, allowing correlation of gas composition with groundwater conditions and supporting more complete borehole characterisation. Compatibility with alternative manufacturer software (such as Instrument Connect) via the Gas Data portal extends data-management options and allows integration with existing client or consultant systems.

GasData GFM436 is intrinsically safe and certified for use in Zone 1 hazardous areas, supporting ground-gas and landfill gas investigation in environments where flammable vapours may be present. By monitoring methane to LEL and capturing the associated gas regime, it supports assessment in line with UK guidance and standards such as Part 2A EPA 1990, BS 8576, CIRIA C665 and BS 8485, helping organisations demonstrate compliance and inform mitigation design.

The analyser combines Gas Data’s proprietary NDIR technology with industry-standard sensors and transducers to deliver stable, repeatable performance. An annual service and calibration interval is clearly defined, with calibration status shown on the home screen and on the calibration certificate, simplifying audit trails and providing clear evidence of instrument validity for regulators and clients.

GasData GFM436 integrates readily into existing monitoring programmes and can be configured within its fixed configuration family to the specific gases required from the available sensor list. It is supported by an established service network providing calibration, repair, spare parts and consumables, with technical support, product training and demonstrations available via distributors and the manufacturer. Instruments are built to order, with typical lead times communicated at order acknowledgement, and may be purchased or hired with defined service options and support packages. Although GFM436 is no longer in production, an equivalent analyser (GM25-4) is available for users seeking comparable functionality and continuity of ground-gas monitoring capability.