Expertise in fire and gas detection

Nowadays, it is very difficult to duplicate a single fire and gas detection strategy in all industrial projects or existing sites. Indeed, the environmental, economic, technical and operational contexts specific to each site and project make it necessary to define a specific strategy and philosophy. 

This explains why SAFENGY always recommends the definition of a fire and gas detection philosophy so that Client and potentially authorities, emergency services and insurers validate the principles that can be applied to the project or to the existing site. 

It is really important to define the type of detector to be installed. At the fire detection level, detectors can be of punctual or linear smoke optic type, thermostatic (heat detector), thermo-velocimetric (heat detector), flame optics (UV, IR, UV/IR; IR3, IR4) depending on the type of fire encountered (hydrocarbon, gas, hydrogen, solid fuel, etc.). For gas detectors (toxic or flammable), they can be of punctual or linear infrared type, catalytic, electrochemical or semiconductor depending on the type of gas to be detected (e.g.: IR for hydrocarbon fires, catalytic for hydrogen and electrochemical fires or semiconductor for the presence of hydrogen sulphide – H2S).

It is also necessary to define  the principles of locating detectors. For rooms or common buildings, the installation of fire detectors (smoke, heat) will be relatively easy by applying recognized rules and regulations such as CNPP APSAD R7 applicable specifically in France or NFPA 72 standard generally applicable to international projects.

On the other hand, the location of optical flame detectors or gas detectors is very specific and requires expertise. This is why it is necessary to give the principles validated for this type of detection.

In addition to the location of detectors, the question of the redundancy or not must be asked. Indeed, the choice of redundancy or not of the detectors depends on the level of reliability of the execution of automatic safety actions. Thus, a Client who wishes to set up a fire and gas detection system initiating automatic actions and alarms will be worth considering redundant detectors to improve the reliability of its fire and gas detection system and thus avoid any automatic action in the event of accidental trigger of one detector.

But beware, for obvious economic reasons, the redundancy of detectors does not mean necessarily double the detectors at the same location. It is therefore necessary to work on optimization of the location of detectors in order to enhance them (1 detector must cover as much as possible multiple areas). Finally, in the event of detector redundancy, it may be envisaged to group these detectors in voting logic in order to minimize false alarms and spurious trips. For example, an automatic action can only be initiated if two out of three detectors detect the accident; this is called confirmed detection.

Once the steps described above have been completed, all the actions and alarms in case of confirmed detection can be set.  Actions are for example, starting the fire pump, deluge valves, sending a signal to the safety PLC, shutdown the installation, isolating certain sections of the process, the emergency depressurization… 

On-site visual and lighting alarms must be planned and located at strategic locations. With the exception of noisy places (pump station, compressor room, etc.) which are most often equipped with visual alarms, the entire site must be properly covered with audible alarms. Finally, in addition to these alarms, manual alarm call (MAC) points are also strategically distributed on the site.

Once the alarms and actions are set, the overall information must be      summarized in a document called fire and gas detection cause and effect matrix.

As mentioned in the previous paragraph, the definition of the location of the detectors requires specific expertise.

Indeed, although the installation of fire detectors (smoke or heat) in closed rooms or buildings is relatively easy, it requires a more detailed study for the optical detection of flame and the detection of gas (flammable or toxic).

That is why, for these three types of detectors, it is important to develop and apply a hazard analysis whose results allow to define precisely potential sources of hazards, identify the associated risk (fire and/or flammable gas and/or toxic gas) and install the correct number of suitable detectors (in accordance with the fire and gas detection philosophy).

Thus, within the framework of the analysis, if a source of potential leakage of toxic gas is identified at a pump location, the recommended number of toxic gas detectors (from the      technology retained in the fire and gas detection philosophy) is mentioned.

The analysis will be based on all available data and information. It can be: equipment layouts/plans, P&IDs, PFDs, heat and mass balance sheet (HMB), list of stored products, operating and/or ambient conditions, etc. The more information available is detailed, the more precise the analysis will be.

In the context of studies for existing site, a site visit is essential in order to identify all useful and necessary information for the completeness of the analysis.

This analysis constitutes for any Client a real support in the event of a request from the authorities or insurers. This study simply demonstrates that a rigorous and serious study was implemented within the framework of the installation or renovation of its fire and gas detection system. 

This type of document must be considered as a live document since it must be adapted to any changes to the site.

Based on the analysis carried out beforehand, one or more layouts for the fire and gas detectors must be developed.

Several methodologies are possible which will be particularly dependent on the final objective. It can be considered the 3 below methodologies     :

✔ Quantitative 3D
✔ Qualitative
✔ Quantitative 2D

If the final objective is to have an extremely precise location of the detectors, the 3D quantitative method is preferred. The study associated with this methodology nevertheless remains very expensive since it requires the use of specific 3D software. The site or facilities must have a 3D model in Navisworks or PDMS format or another format compatible with the 3D software used.

For gas detectors, the study consists in particular in identifying spheres of detection and ensure that all areas are covered by one or more gas detectors depending on the chosen philosophy (redundancy or not, automatic or manual actions on detection, etc.)

A more complex methodology integrates the plume of the gas cloud obtained by 3D modeling of a leak for more precision but requiring a cost of the study a lot more expensive.  

Finally, generally applied for flame detectors, the vision cones are represented on the 3D model in order to verify the coverage of the flame detectors and to verify that obstacles or other obstructing objects do not decrease their effectiveness. And similar to the gas detectors, the graphical representation of the detection cones enables the check of the redundancy or not of the detectors, always depending on the philosophy adopted.

If the final objective is to quickly and easily locate detectors, the following methodology is recommended. It simply consists of setting up the detectors according to expert judgment based on a set of criteria such as, for example, the size of the installations, the efficiency of the detectors, the direction of the prevailing winds, etc.

The last methodology, which ultimately is a compromise between the first and the second methodology, is based on the results of simulations of accidental scenarios (flammable gas leak for example) obtained using 2D software. The detectors are installed according to the results obtained, for example according to the extent of the flammable gas cloud determined by simulation.  

Whatever the methodology used, the final objective is to propose an installation of the detectors on a layout. This layout will ultimately be the result of engineering and development of a fire and gas detection strategy, of a specific hazard analysis and of the application of a methodology for setting up detectors.