Flame and Gas Detection

Flame and Gas Detectors for High-Risk Industries

Many oil and gas facilities are located in regions with extremely harsh weather conditions: very low temperatures, powerful winds, snow and ice, intense sunlight, high temperatures and, at times, sandstorms. Flame and gas detectors are installed in these environments. In all of these locations, and in many other industrial settings, there are various background IR or UV radiation sources — some of high intensity — that must be distinguished from the radiation emitted by an actual fire. These conditions create real obstacles for optical flame and gas detectors. Extreme ambient conditions can be directly linked to false alarms being triggered on a regular basis.

The consequences of a false alarm matter: confidence in the detection system is eroded, and unnecessary activation of emergency procedures carries a real cost. This is why it is critical that flame and gas detectors are not triggered by ambient environmental factors.

To meet the safety requirements of these facilities, reliable flame detectors can be installed to provide fast, dependable fire detection even under these demanding conditions, and open path flammable or toxic gas detectors can be used to detect the presence of any released gas before its concentration reaches a level that would cause a fire, an explosion, or a risk to personnel.

Because of all these conditions, the oil and gas industry requires detectors to be tested and certified to the highest standard, and to carry the approvals needed to prove they are “fit for purpose.”

Some of the key approvals required include hazardous-area explosion-protection (ex) approvals (FM, CSA, ATEX, IECEx, Inmetro, CU TR), functional approvals (FM, EN) and a reliability approval (SIL2 TÜV).

Optical Flame Detection

Several optical flame detection technologies work on the same basic principle but detect at different optical wavelengths, and therefore detect different types of fire. The two main types of optical flame detection used in the oil and gas industry are combined UV/IR and triple infrared (IR3) detection.

UV/IR Detection

UV/IR optical flame detection is dual-spectrum: it uses a solar-blind UV sensor with a high signal-to-noise ratio together with a narrow-band IR sensor. UV/IR detectors are particularly fast against flash fires and have good immunity to false alarms.

The UV sensor is a good but overly sensitive fire detector on its own, so it is complemented by an IR sensor operating in the 2.7µ or 4.3µ spectral bands characteristic of fire, which confirms that a genuine fire is present. The result is very fast fire detection with high reliability.

Triple IR (IR3) Detection

IR3 optical flame detection uses three IR sensors to monitor the selected area: one sensor detects the infrared radiation emitted by the hot CO2 combustion product of a fire, and two reference sensors are sensitive to background radiation at longer and shorter wavelengths. Both are analysed to confirm that the detected pattern matches a genuine fire condition.

IR3 detectors can detect at very long range and have excellent immunity to false alarms.

An IR3 detector can detect a standard 1ft² (0.1m²) gasoline fire at a distance of up to 215ft (65m).

IR3 vs UV/IR

As always, the choice here depends on the application. High-risk industries need the most robust detector — one least prone to costly, misleading false alarms.

IR3 technology has the highest immunity to this kind of false alarm and offers a much greater detection range (215ft/65m for a 1ft²/0.1m² gasoline fire, compared with only 65ft/20m for a UV/IR type). As a result, it is widely specified for high-risk applications.

In addition, on large or open sites this longer detection range is a way of reducing the number of detectors needed — including the associated cabling and control-panel loops — and therefore the total cost.

That said, there are many lower-risk applications where range matters less, where a UV/IR detector is more than adequate for the job, and where its lower cost is also an advantage.

Open Path Gas Detection

Open path gas detection, also known as open-area gas detection, is a reliable method of detecting flammable gas concentrations at distances of up to 660ft (200m). Open path gas detectors can detect these flammable gases at both low and high concentrations.

When a gas leak occurs, it forms a gas cloud whose concentration decreases towards its edges, so any part of the gas cloud can be detected by an open path gas detector.

It is important to detect a gas hazard before it causes a fire, so that neutralising measures can be applied before hazardous concentrations are reached. Open path gas detectors cover a wide area and provide a very fast response.

The detectors consist of a transmitter and a receiver placed at a pre-determined distance from each other. The transmitter projects a beam of light to the receiver. When flammable gas passes through the beam, it absorbs some of the light radiation, reducing the signal at the receiver. These signals are analysed and the output signal is fed to a control system.