Three Levels of Detection – Safety Monitoring: Combining Technologies for Reliable Results

At any industrial plant, well site or offshore platform the detection of flammable and/or toxic gases and vapour and their potential ignition is a critical activity. But navigating the evolution of detection technology, finding the optimum system to protect people and property isn’t a simple task, particularly since no single system or technology is the solution to every application’s problems.

The following addresses the fundamental choices available in detection and possible combinations of technologies that may solve problems while protecting lives and property. The vulnerabilities of any one detection solution are offset by the strengths of the others when utilizing a comprehensive approach to coverage.

Today, five main types of fixed detectors are available: Point-type detection; line-of-sight detection (open path); ultrasonic leak detection; and flame detection.


Point detectors are permanently mounted often in enclosed areas to monitor for the presence of toxic or flammable gases. These systems must be installed to provide protection of assets and people working in areas where there is a potential gas leak to occur. These safety instruments are calibrated for the type of gas to be detected, and require regular maintenance and inspection for optimum performance.

Net Safety Monitoring Millennium II H2S & LEL Transmitters

Also requiring strategic placement and careful alignment, line-of-sight (or open-path) detectors monitor for gas occurring within the zone of a beam of infrared light projected between two points. These detectors are calibrated for specific gases.

Some examples are the Spectrex Line-of-Sight (Open Path) Combustible detector consists of a Xenon Flash infrared transmitter and infrared receiver, separated over a line of site from 7 to 200 meters.

The Spectrex Line-of-Sight (Open Path) Toxic detector consists of UV detection technology and detects Hydrogen Sulfide and Ammonia gas with path lengths up to 60 meters.

Both technologies are built for reliability and continued operation under extreme environmental conditions. These Line-of-Sight technologies require no calibration and limited maintenance.

Spectrex SafEye 700 Open Path Gas Detector
Spectrex SafEye 700 Open Path Gas Detector

Ultrasonic gas leak detection uses acoustic sensors to identify fluctuations in noise that is imperceptible to human hearing within a process environment. Unlike traditional gas detectors that measure accumulated gas, ultrasonic gas detectors “hear the leak, triggering an early warning. These detectors are engineered to withstand the most extreme conditions and are a non-consumptive sensing technology that doesn’t require calibration, reducing maintenance and cost-of-ownership.

Emerson Incus Ultrasonic Leak Detector

The most common flame detectors identify flames through optical methods like ultraviolet (UV) and infrared (IR) spectroscopy. Flames are typically fuelled by hydrocarbons supplied with oxygen and an ignition source, which generates emissions of UV and IR radiation as part of this reaction. Flame detectors are designed to detect this energy at specific wavelengths, which allows them to discriminate between flames and false alarm sources. When selecting a flame detector, performance criteria includes: hazard to be detected (i.e. fuel type); intended environment (potential false alarm sources or attenuation sources); response time of the detector and self-diagnostics.

Rosemount 975 Flame Detector

Detection systems alert users when a fault condition has occurred and typically initiate a corrective action automatically. Since it’s critical that alarm settings be sensitive enough to detect unsafe conditions, false alarms are a problem.

False alarms can be triggered by other gases or vapors in the area, background gases, sensor drift, or in the case of flame detectors, background UV or IR energy sources. One possible solution is to employ a voting system where two or more detectors must both indicate an alert condition for the system to trigger an alarm.

The factors to consider when determining alarm settings include: the inherent risk of the gases being measured; the typical background level of gases; the proximity of people; time required for alarm response; what must be done to correct the hazardous condition; and the particular code requirements at the installation site.

Combining Technologies for Optimum Effectiveness


Safety systems that deploy a diverse range of detection technologies can counteract the serious impacts of gas leaks and the potential for fire and explosions. A combination of ultrasonic leak detectors, fixed gas monitors, and flame detectors are particularly effective because they’re complementary and cover the three detection defence levels.

The first stage is the immediate leak stage, which has the greatest opportunity for fast and effective mitigation the second is during the gas cloud formation or accumulation stage, which is a very serious safety condition; and a third is during the ignition stage, which can be catastrophic.

Ultrasonic detectors are often installed outdoors to cover wide areas with challenging detection conditions. Point detectors should be installed at or near known high-risk gas leakage points or accumulation areas to provide information on the level of gas present in these areas. Open-Path gas detection systems are most effective at plant or process area boundaries. They monitor the plant perimeter and provide an indication of the overall gas cloud movement in and out of the facility.

The movement of gas clouds throughout the facility is tracked by monitoring the output signals of all the gas detectors within the safety system. Optical flame detectors monitor wide areas for IR or UV energy related to the ignition of a gas source and provide instant alarm condition back to notification and mitigation systems.

A variety of challenging factors affect the performance of these technologies: location (indoors/outdoors); airflow; gas properties (type, density, buoyancy); environmental conditions like temperature and humidity; background conditions (false alarm sources); and obstruction. Best practices for each application will be different, but it’s critical to perform proper HAZOP analysis and identify the sequence of events leading up to an incident.

Every safety engineer that is committed to safeguarding personnel, plant, and productivity, and employing a system that provides comprehensive, tiered coverage can yield optimal results before an escalated incident occurs.

For years now, detection gas leaks has been accomplished through the use of various point detectors along with open-path infrared perimeter detectors. While no single sensing technology solves every situation, users can now greatly extend the coverage provided by those solutions as well as overcome some of their serious limitations, through the use of ultrasonic leak technology.

With a combination of detection technologies, hazards have fewer chances of propagating undetected. Such diverse safety systems, combined with a design that mitigates leakage and eliminates possible ignition sources, provides a sound approach for delivering reliable coverage in any hazardous environment.

Full Line of Industrial Flame and Gas Detection Systems

Westech Industrial is the exclusive supplier in Western Canada of Net Safety / Rosemount industrial Flame and Gas Detection Systems. These systems are designed to excel under the toughest conditions to help you streamline day-to-day operations and, more importantly, keep your people and assets safe.

We are also a preferred partner with Kenexis the creators of Effigy a forefront Fire & Gas Mapping software that enables individuals to determine the optimal location for installation of flame and gas detectors that will result in a safe environment while achieving a lower capital expense by optimizing technology and detector placement.

Westech provides our customers with quality flame and gas products stocked in our Calgary, Edmonton, or Grande Prairie offices while offering 24/7-customer service support.