technology: north sea oil rigs will be safer by design - stainless steel natural gas grill

The North Sea oil platform, built by Jeff Kluk Piper Bravo, will start producing oil this month to replace Piper Alpha, which was exploded and fires in July 1988
The lessons of Thealpha disaster have brought a safer design to its successor.
Strict new safety regulations were released this week and will take effect on all new platforms in the UK region in the North Sea in six months.
The destruction of Piper Alpha began with a mass of flammable gas leaking into a partially closed part of the platform and exploding.
The explosion is believed to have broken through the firewall, allowing smoke and flames to enter the control room and preventing the crew from starting the fire pump.
Early regulations set out some aspects of platform design.
According to the Karen survey, which investigated the disaster, the new regulations pushed the security responsibility to the platform operator.
By 1995, they will have to make a document called "security case" for all platforms.
This will detail all possible hazards and how to prevent them, which must be accepted by the health and safety supervisor.
The cost of implementing all security cases in the UK sector is estimated to be 1. 5 billion.
About half of them will be used to provide a temporary safety shelter (TSR) for each platform to protect workers for more than an hour.
Platform operators must conduct outrisk analysis studies on all possible fires or explosions and show that the probability of TSR failure is less than 1000 per year.
The intensity of the fire on the island of Piper Alpha shows that this is not easy to do.
Few workers on the platform lived for more than 20 minutes, and the structure of 34 000 tons was almost completely destroyed in 90 minutes.
Over the past four years, how the gas cloud is ignited in the process area of platform congestion has always been a major research area.
According to David bull of Shell's Sandton research center near Chester, flame expansion consumes gas and air, and its speed depends on the burning speed.
When the flame hits an obstacle, the resulting turbulence increases the combustion speed.
The more complex the obstacle, the greater the flame acceleration, the greater the possibility of damage.
Predicting these effects is extremely complex, and researchers have tried physical models and computer simulations.
There has recently been a major improvement in finding that in the scale model of 1:12, the behavior of the mixture of ethylene and air is similar to that of the completesize explosion.
The flame speed of ethylene is faster than methane in natural gas, which cleverly offsets the small size of the model.
The Thornton Center recently tested this method.
The researchers built a scale model of the two platform parts at 1: 12, covered with clingfilm, filled them with a mixture of ethylene and air, and then lit them.
During the test, they found that complex structures on the rig, such as pipe nests, produced a flame speed of 400 per second.
Outdoors, the flame front travels at a speed of 4 metres per second.
On August, The Sandton center completed the experimental work to verify the computer model of the explosion.
In the work, researchers found the largest 12 test explosions ever.
The gas is in an open
10 by 9 by 6 m end type steel box-enough to accommodate six container trucks.
The only way to check if the spelling of the model is correct, says Bull, is to measure something close to full size.
Last month, the British gas company launched a software package called Chaos designed to simulate the release of flammable materials and subsequent explosions and fires.
The model is specifically tailored to the requirements of the new security legislation.
In practice, by separating the living area from the processing plant, the security of the modern platform has been improved.
The Piper Bravo has a longer narrow deck, its predecessor is a huge stainless steel
Steel wall separating the processing plant from the living area.