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Buncefield and beyond

(Thu 25th Sep 2008)

Ceyhan battlers

Storage Tank Fire Protection

Buncefield has become an iconic

incident in the extremely limited

pantheon of major UK tank fires.

It joins a select band of

“once in a career” fires that have the

ability to change thinking

amongst professionals.


However, we have to go back as far as 1981to find Europe’s
trigger for what we might call the new wave of tank
firefighting – there was a realization that aspirated
low volume foam application had serious shortcomings.

Tank 80X1 at Mobil Oil, Coryton refinery was the ground
breaker at that time as it brought about Europe’s first
realistic and thorough full surface tank fire fighting
appraisal project carried out jointly by Mobil Oil, Shell
UK & Essex County Fire & Rescue Service. It culminated
in the development of Europe’s first refinery full surface
tank fire fighting procedures.

Both large volume non aspirating monitors of 22,000 &
37,500 lpm were evaluated along with the first realistic
practical appraisal since the 1930’s of both the correct
type of foams to use and the foam  application rates to
be effective. We saw the introduction of an application
rate of 10.5 lpm/m2 (against the previous Europe wide
6.5 lpm/m2 norm at that time), with the largest tanks
being 76 metre diameter crude oil open floating roof
tanks.

Between the Coryton and Buncefield fires, the 1983
Tank 11 fire, at the then Amoco Refinery in
Milford Haven, also generated huge media interest as
the second in the trilogy of major UK tank fires within
many people’s living memory. Even if tank fires are
rare in the UK, a significant number of fires occur
annually on a worldwide basis. Given that most large
tanks are of the floating roof tank variety, it follows
that guidance on how to extrapolate fire protection
guidelines from smaller tanks to the huge fire risks of
today should be given serious consideration.

With ongoing research into tank fires being
coordinated through the LASTFIRE project and historical
data available from media sources, this contribution
will take an overview of both fixed and portable fire
protection methods.

Assuming that the facility to be designed is in accordance
with a Flammable and Combustible Liquids Code such as NFPA
30, and that suitable tank maintenance procedures are
followed, the strategy can call upon guidelines for
protection contained within NFPA 11 or IP19. Both standards
cover everything from cooling spray rates through to
calculating the quantity of foam concentrate to be stored
and the type of foam delivery to be used. The concern is
always whether the success rates of smaller scale fire
tests can be replicated when faced with a real life incident
and all the variables that real life presents. Equally,
risk assessment should establish whether or not it is
still viable to deal with one tank at a time or to take
the now more widely accepted view that multiple fires
can occur.

The success of fixed systems is always dependent on a
good maintenance regimes, adequate stocks of foam
concentrate and that tank discharge devices are not
going to be knocked out by explosion.

The practicable options can be summarized in
the following categories:

·    Detection & Alarm Systems
·    Detection & Fixed Suppression Systems
·    Fixed Foam Pourer/Base Injection Systems
·    Fixed & Mobile Foam Monitors
·    External Brigade Assistance

Floating roof tanks

Detection and foam suppression stand alone units.
Usually Nitrogen powered with telemetry control back
to the control room. Small foam vessels are located
on the roof to protect the rimseal area. The advantage
of the combined detection system is its speed of response.

Over the top pourers. Provide low expansion foam to the
rimseal foam dam area. Can be fed from a central foam
proportioning system or from a mobile foam tender.
Can be linked to linear heat detection or can be manual.
Williams Fire & Hazard Control have been carrying out
considerable R&D into cone and internal floating roof
tank fires, following a series of these over the last
years.

It was perceived by Dwight Williams and his team that
foaming the surface of the product prior to
extinguishing the fires on these tanks when they are
burning at the vents or fishmouth tears can over time
cause an explosion inside the tank that is likely to
violently blow the roof of the tank. It was during
this research that they fell upon the concept of a
dual agent foam / dry chemical chamber fitted in
place of one of the foam chambers if fitted to these
tanks, thereby allowing firefighters to purge the
atmosphere inside the tank vapour space during the
fire and extinguishing the fire in a matter of seconds.

Cone roof tanks

Over the top pourers, protecting the full fuel
surface and incorporating a vapour seal between
the tank and supply pipework. Can be subject to
explosion damage.

Base foam injection systems are situated remotely
from the explosion area. Rely on forcing low expansion
foam through the base of the tank up to the fuel
surface. Unsuitable for foam destructive products.

Semi subsurface base foam injection systems incorporate
a high back pressure generator and an internal floating
delivery hose to apply foam to the surface of the tanks
containing foam destructive chemicals such as Methanol
or Acetone. A gentle foam application results in faster
extinguishment. A plunging foam application is a less
efficient method of delivery.


Mobile equipment such as monitor trailers and refinery
vehicles with monitors, as with floating roof tanks
require a critical deployment factor involving a
sufficient quantity of foam concentrate and water in
the correct application rate or deployment will not
succeed It is in this area that most development has
taken place with the realization that fully involved
tank fires can be successfully extinguished rather than
left to burn. The use of unaspirated foam applied by
very high flow rate monitors also represents a paradigm
shift from the days of aspirated only application.

The current “record” tank fire is the Orion. The incident
occurred in 2001 and was successfully extinguished by a
team from Williams Fire & Hazard Control in 65 minutes
using an application rate of 8.55 l/m2/min.

The tank was a massive 82.4 metres diameter and it
required a flow rate of 45,000 lpm. Given these big
numbers it is easy to see why foam concentrates are
becoming ever more concentrated with 1% taking over
from 3% and 6%. This means that less product is
required to be stored and transported should the
worst occur.Compare this to 1983 when tank 11 at
Milford Haven was fought in two waves: firstly by
applying foam at a rate of 10400 L/min (2300 imp gpm)
and secondly at 14500 lpm corresponding to an
application rate of 3.0L/m2/mi. 3 canons were lifted
onto the collapsed tank shell to extinguish the folded
shell area.

Since then Williams Fire & Hazard have developed their
Daspit tool, a monitor specially adapted to fix to the
tank wall that allows firefighters to target a rimseal
fire from an above ground position without risking
expensive hydraulic access appliances nor unnecessary
hazard to firefighters.

As Dwight Williams of Williams Fire & Hazard said during
one of their recent incidents:

“The risks here are many – but first and foremost on
everyone’s mind is not to sink the pan. This was a
floating roof tank with a pretty good seal fire on it.
You cannot allow that seal fire to jeopardize the
integrity of that roof and sink it into the product.

If that happens you immediately go from a 2,000 gallon
per minute application to 14,000 gallons per minute!”

“We got everything into place very efficiently and
knocked the fire out 20minutes after arriving!
You can’t accomplish that without knowledgeable
and helpful teamwork.”

The LASTFIRE study indicates a very low probability
of full surface fires on floating roof tanks as a
result of rim seal fires. However, if there is a
spill fire on the roof or an impinging bund fire,
the probability for a full surface increases.
Due to the fact that floating roof tanks are very
often large diameter tanks, they will also create
one of the most challanging situations in a tank farm.

Refineries and fuel storage sites are increasingly
adapting to the needs of high flow monitors and are
investing in the combined infrastructure – monitors,
foam stock, high flow hoses and high volume pumps –
designed to deal with fully involved tank fires.
The greater sharing of information on a worldwide
scale through organisations such as JOIFF
(Joint Oil Industry Fire Forum) is leading to a
consensus that the armoury to fight these fires
includes both fixed and portable equipment.

Where sites are in close proximity to one another,
mutual aid schemes are being developed so that the
infrastructure costs can be shared. It’s not
surprising that this type of specialized resource
is beyond the means of municipal fire brigades when
we consider that they have severe budgetary
restrictions and whose remit is arguably not to
finance the resources for very exceptional
industrial hazards.

References

Thanks to Williams Fire & Hazard Control for supplying

information and photographs.

 

LASTFIRE: The LASTFIRE Project provided an independent
and comprehensive assessment of fire related risk in
large, open top floating roof storage tanks resulting
in a methodology by which site specific Fire Hazard
Management policies can be developed and implemented.
It therefore represents a major advance in the
knowledge of this risk. Resource Protection
International www.resprotint.co.uk Joint Oil Industry

Fire Forum: www.joiff.com

 

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