When it comes to fire safety, technology can be deployed to ensure that a small fire does not become a big one, explains Andy van Vloten Martin
The focus on safety of an offshore asset has never been as important as it is now and going forward into the decommissioning phase, where the risks associated with safety and environmental critical elements are very different.
Many of the assets are operating way beyond their design life, and fire safety systems that are installed have been in place and operational since the asset first came into service. On other assets, they have been modified or replaced as the functionality changed. Conceptually, however, the emphasis has been very traditional - using established fire detection and protection solutions, splitting the asset into modules and preventing escalation between modules. In the event of a fire in a module the damage can be extensive, and for normally occupied areas this is more likely to result in panic.
For switchgear and normally occupied enclosures, there is a variety of gas suppression systems that either flood the room with inert gas to reduce the oxygen concentration, or chemically react with the fire to remove the energy from the flame. Following a discharge, large or heavy gas cylinders will be replaced with recharged ones, which is time consuming and expensive. The safety expert Blaze sets out to minimise the likelihood of unwanted discharges by implementing a system that works on the voting of fire detectors. This is where more than one detector needs to go into alarm before the system is initiated and in the event of a fire it must be of a minimum intensity to be detected. The larger the fire, the harder it is to control and ultimately, extinguish. There is a balance between detecting it early enough to be still small and thus able to extinguish, but not at the expense of an unwanted release.
Detecting the fire early is relatively easy by using sensitive detectors and more of them, however the challenge is whether to act on the information or investigate further. Very early smoke detection apparatus (VESDA) has become more sophisticated in recent years to now pinpoint the products of combustion to the specific sampling tube, which aids tracing the source but still requires intervention to suppress.
Fires require an ignition source. This is often an electrical short circuit caused by dust, liquid ingress or component failure. Due to the nature of safe area switchgear and control equipment, it is housed in small boxes to protect it from mechanical damage, but the boxes have louvres to maintain an airflow, keeping them cool in normal operation. In the event of a fire, the airflow feeds the flame, creating a chimney effect and quickly becoming larger than a single flame. A total flood inert gas suppression system in the room will reduce the oxygen concentration below 15% but takes longer to suppress the fire in the box as it must penetrate through the louvres first, by which time the fire damage is more extensive than it could have been.
Protecting the enclosure
Protecting the box rather than the room and tackling the fire when it is small, is the best approach for minimising fire damage and has a higher likelihood of being successful. Enclosures rely on being relatively gas tight, having a hold time following release of a gas suppression system of greater than 10 minutes. Warped doors or damaged seals, service transits and enclosure modifications all lead to poor enclosure integrity and thus the effectiveness of total flood.
Small cabinets of less than 2m3 can easily be protected with small cylinders of less than nine litres, depending on the agent, which are easily transported, fitted and low cost to replace. Systems can be designed to operate entirely mechanically such as a frangible tube, that bursts when in contact with a flame. Passing this frangible tube around the equipment within the cabinet releases agent out of the burst hole in the tube. Alternatively, the frangible tube can be used to detect the fire and the agent released through dedicated pipework to nozzles, effectively flooding the inside of the cabinet where the flame has been detected. Relying on a frangible tube as the detection method requires no external power, control logic or battery backup – all of which add an extra layer of complexity that needs to be managed. If the frangible tube is used as the means of delivering the firefighting agent, the tube will always burst at the hottest place in the cabinet and thus the discharge is conveniently adjacent to the fire.
The best of both worlds can realised by having both cabinet protection in addition to the existing room total flood, which would mean that the small fire is suppressed with the supplemental system, but in the event of escalation, the enclosure protection is released as a backup. In any event there is an intermediate step to help prevent the large inert gas cylinders from being discharged.
Moving forward with decommissioning of older, obsolete assets becoming more prevalent, the use of containerised temporary control equipment is likely to be more popular. In the decommissioning phase and cessation of production, the asset remains connected to live wells and process, known as warm suspension prior to entering cold suspension where the asset may either remain manned or transition to being unmanned before finally progressing into removal or dismantling.
As the process begins for draining down liquid hydrocarbons and breaking containment, the type of risk from fire and explosion on the asset change. There is potential fire risk due to the opening of hydrocarbon containing equipment, hot working and sparks from cutting and grinding. Care needs to be given to the levels of detection in place as long duration pool fires are replaced with the increased risk of explosion from gas fractions being ignited. Are these gas fractions lighter or heavier than air? Do we detect at high or low level? Have we got means of dispersing and preventing the accumulation of flammable gases?
When containment has been broken, it’s too late to start playing catch-up. With the increased potential for ignition being prevalent, we have no means of isolating, although fires are likely to be of a lower intensity and perhaps even tolerable to allow a controlled burn.
The emphasis now shifts onto portable fire and safety equipment. Portable detection is different to that required for a production platform. Blaze uses wireless devices interconnected to local panels that can be interrogated remotely via IoT and can assess and respond quickly to the release of toxic and radioactive substances. The Rapid Deployment Kit includes GPS-enabled monitors, a Link3 wireless router and all necessary accessories to create a perimeter and set up a command station up to two miles from the site.
For decommissioning, rental products can be utilised that can be integrated into systems easily and rapidly. These will be required for relatively short durations in the field and a rental option means that the operator does not have the outlay of having to own infrastructure on a retiring asset.
Regardless of the stage in the life cycle of the asset, the most important factor is continuing to ensure the safety of our engineering workforce and reducing the possible damage to the asset, no matter how big or small the fire.
Andy van Vloten Martin is fire safety engineer at Blaze Manufacturing