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Self-contained water-atomising fire suppression for offshore installations

21st February 2013


Alan Elder reports on a low-pressure system that is specifically engineered to deliver total flooding fire protection.

A new self-contained water-atomising fire suppression system - Ansul Aquasonic - aimed at Class B fires that involve flammable liquids such as petrol, diesel, solvents, lubricants and spirits as been unveiled by Tyco Fire Suppression & Building Products.

Typical applications include turbine package enclosure protection for offshore production installations. It is being heralded as a technically advanced solution that quickly and efficiently suppresses fires while discharging a minimal amount of water. The new system utilises non-toxic and readily available extinguishing media - water and nitrogen.

Aquasonic is a low-pressure system that is specifically engineered to deliver total flooding fire protection for a wide spectrum of special-hazard applications in defined-area protected spaces, including flammable liquid stores.

The system has been fire tested within compartmentalised areas and found to be effective for the suppression of a wide variety of exposed and shielded Class B hydrocarbon pool and spray, and gravity fires. It is safe to use in occupied spaces, does no harm to the environment and is inexpensive to recharge. Enclosure integrity tests are unnecessary, as the system has been tested and approved in 'open door' conditions.

The key to the effectiveness of the system is the patented Aquasonic atomiser nozzle. It uses what is described as 'supersonic' technology to break down water particles into trillions of smaller droplets that are uniform in size.

As these droplets reach their target they extract heat from the fire and suppress it. They also dilute flammable vapours by the incorporation of water vapour, and provide cooling of liquid hydrocarbon fuels below vaporisation temperature.

Significantly, the Aquasonic system uses one-third of the water of comparable high-pressure water-mist systems, produces a higher volume of smaller water droplets than traditional watermist solutions, and projects them farther across the combustion zone than was possible with previous technology. Two Aquasonic atomisers produce 1.5 trillion super-fine water droplets every second, producing a total surface area of 121 square metres every second.

The system can protect a potential hazard with a free volume up to 260 cubic metres with two atomisers that create a minimum 10-minute discharge plume of water droplets.

The importance of droplet size cannot be over-emphasised. The smaller the droplet size, the more surface area is available to absorb heat and, ultimately, extinguish the fire.

The key to the effectiveness of the Aquasonic system lies in its ability to create a high volume of amazingly small droplets from very little water.

The system uses a very efficient means of creating water droplets to generate turbulence in an enclosed space. This helps to distribute the water evenly and at high velocity, enabling it to penetrate all of the nooks and crannies to help suppress the fire as quickly and as efficiently as possible.

The Aquasonic system may incorporate an Autopulse control system that is designed to detect fires and activate fixed fire protection systems. This automatically activates the Aquasonic system after receiving an input signal from one or more initiating devices; either a manual pull-station or detector. The control system has its own internal power supply, emergency batteries and solid-state electronics.

The moment a fire condition is detected, the detection and control system actuates the Aquasonic system, which contains nitrogen storage cylinders and a stainless steel water tank. These nitrogen cylinders provide pressure to drive the water to the system atomisers.

When the system is activated, quick-action valves on the nitrogen cylinders open and the gas pressure flows through pressure regulators, which maintain the pressure at 8.6bar (125psi). This pressure drives the water through the opened water valve to the system atomisers. The Nitrogen discharge also provides the necessary pressure to create the water discharge plume.

Aquasonic is a flexible system that is easy and inexpensive to install; one that does not have the stringent spacing requirements demanded by other systems on the market.

The system has few moving parts and uses tried-and-tested technology that has decades of proven performance. Detection and actuation can be automatic and/or via remote manual operation.

The system is supplied in the form of a pre-packaged Aquasonic supply skid that houses nitrogen storage cylinders and a 189.3litre (50 US gallons) water storage tank. This skid assembly also contains the necessary valves, hoses and manifolds, all of which are mounted securely on the skid base for ease of transportation and positioning in the appropriate location.

This new Ansul system is Factory Mutual (FM) approved, and extinguished all of the fire scenarios in the FM protocol in less than five minutes. This even included those scenarios where the FM protocol did not require the fire to be extinguished. The system also complies with NFPA 750 (2006) (Standard on Water Mist Fire Protection Systems), and is capable of operating in a temperature range that spans from 4°C (40°F) to 54°C (130°F).

www.engineerlive.com/iog

- Alan Elder is Sales Director, Commercial Suppression EMEA at Tyco Fire Suppression & Building Products, Manchester, UK. www.tyco-fsbp.com







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