This paper will present a brand-new stand-off gas detection system using a multispectral infrared imaging technology. This system allows seeing the size, localization and behavior of a gas cloud in real time. The goal of this system is to enhance the level of safety and security in petrochemicals plants. This is possible thanks to a new redundant technology which allow the safety units to use a camera to globally monitor the dangerous areas of their installation. By multiplying technologies involved in the security monitoring process, it is possible to reduce the number of misdetection. The main goal of this paper is to describe the involved technology and results which can be obtained by using such a system to detect gases cloud propagating in dangerous environments.

The principle is based on physical properties of gases. Each gas has its own absorption spectrum and can present typical absorption lines in infrared LWIR bands (8 to 14 µm). The system uses the particular pattern lines which enables them to be identified from several gases. The system uses the scene background as an infrared source, and image processing algorithms to highlight the presence of a gas cloud in the field of view. The evaluation of the quantity of gas is carried out by a three differential infrared imaging process: spatial, spectral, and temporal fields.

This technology has been developed several years ago in partnership with the French Defence Agency (MoD). The goal was to meet the requirement for an early warning caused by a chemical threat. With a night & day efficiency of up to 2km and 60°filed of view, this process is able to detect all main gases such as Toxic Industrial Compounds (TICs) and Inflammable Gases (IG). Only some gases cannot be detected because they don't have any absorption line in the LWIR (Cl2 or HF for instance).

The system measures the concentration along the line of sight and this paper will detail the sensitivity that can be obtained like 2 ppm.m for SF6, 35 ppm.m for SO2, 260 ppm.m for NH3 or 500 ppm.m for C2H4.

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