Lázló:
I think you need a quick radiation calc.
Is the flare 100 m up, in which case it *is* very high?
So high, that unless the flare is very big, it won't heat much up at ground
level.
My engineering guess is that our fire water ring will not be disturbed by
the flare.
Water in the pipe is one mitigation preventing large overheating of the
pipe. I bet you could get someone to do some computational-fluid-dynamic
modeling of it. But, start with a simple hand calculation.
1. Determine maximum and median size of flare (approximate flame volume)
2. Determine duration of each flare size
3. Do radiation calcs for flame volumes
a. 0th order, assume point source at centroid of flame volume or,
b. take worse case and put point source at mouth of flare tower
c. due a full radiation calc with configuration factors and atmospheric
absorption
Having said that:
fire water supply mains at oil and gas facilities should be buried. It is
a strategy some refineries and terminal operators opt out of at design
stage because they want easy access to the pipe for maintenance. If soils
are hot with chlorides and sulfates (common to the GCC), this will preclude
steel pipe and promote carbon-black HDPE for service longevity.
If our fire water ring is above ground when the big initiating event
comes...the only ring left will be that
'burning ring of fire.'
Big initiating events are rare. But devastating. These large-sized
terminal loss-events are in the 1/4- to billions- of dollars (not including
environmental clean up from foam), but they happen (e.g. Buncefield,
England; Japur, India; San Juan, Puerto Rico; Reynosa, Mexico; Amuay,
Venezuela, etc..]). Design judgments on terminal and refinery fire
protection are on occasions being made to 1960's Code prescriptions--rather
than to lessons Mother Nature has shared with us here in the last 10 years.
Oil and gas administrators spending serious money on fire protection
should get an education about what large iniitating events can do, and
consciously make a decision about how they desire to approach these
hazards. A lot of automatic systems in oil and gas look good on paper, but
just don't deliver either due to maintenance negligence or even more
poignantly, because the initiating fire event simply blows them away.
Scot Deal
Excelsior Fire/Risk Engineering
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