I am capable of insulting myself.
Your subject title suggests airport concourse glazing, which leads one to
NFPA 415.
Your first numbered item suggests glazing protection from
exposures-in-general.
these are similar, but different standards.
NFPA 415 requires fenestration protection ONLY within 100 ft of fuel release
points.
Even THAT is a large conservative prescription, since there is no
consideration of:
view factors from fire to the window,
size of window,
life & property hazard protected by window
design fire size (e.g. when is a 'spill' a SPILL?, 1 gallon, 1000 L, a
bowser, etc.)
design fire probability
window glazing properties.
Personally, it seems this 100 ft prescription is well intentioned, but all
too often results in
a license for window sprinkler manufacturers to print money on installations
that dont need them.
While the tall windows at Frankfurt Main airport ( approx 10 high looking
out onto the taxiways)
do offer wonderful views, they too provide some protection from the fire
hazards of airport
operation. So we should want to protect these windows from breaking due
to fire; still it is
a reasonable question for AHJ and Fire Authorities to ask, ' how often
have we had
tarmac fires break such window glazing/fenestration?´ Fire protection
need be
provided, IF there indeed is a large enough possibility that the glass
will break from a fire insult.
After all, we don´t even design for protection of airplane impact in the
construction material
and construction design of nuclear pit conversion facilities. In part
because there are other
mitigations that are more effective, in part because the event
probability is too low.
Terry Shultz posed this very question of airport-concourse window protection
in the 2007 Report on
Proposols to the NFPA 415 committee.
His calculations demonstrated that fires needed to be closer than 50 ft
to have a chance at breaking
windows. He also noted that tarmacs were sloped to drain fuel spills
away from most glazing exposures.
Committee rejected Terry´s
proposal-to-allow-glazed-fenestration-in-lieu-of-
sprinker-protection for windows at distances from 50 to 100 ft from a
potential fuel spill. Committee´s
logic was, there is no fire test evidence to validate his calculations,
and the potential fire spill COULD
occur at distances closer than 50 ft to the window.
This begs the question, ´when is a spill a SPILL?´ When is it time to
insult the engineer? When is
it time to insult the Fire Authority supporting this prescription? If the
fire authority upholds this
prescription when a 100 gallon spill can occur within 50 ft of an airport
concourse window, then
we have 'Death of Common Sense´. Batch spill fires burn out in several
minutes.
Cutting to the chase, one could reverse engineer this situation. Do either:
1. a field fire test, or 2.
run the BREAK (or similar) window models with the FDS fire effects model ---
to find a spill fire of Jet A1
(suspending belief in gravity and sloped surfaces for the moment) that at
100 ft distance, IS
capable of breaking the glass. Then ask ourselves, given the enormity of
this fire, ´are we
feeling lucky today, punks?´
Window sprinkler manufacturers and concerned airport managment authorities
and life safety engineers
alike will then reasonably say, ´the fire could be closer than 100 ft to the
windows.´ They would be dead right.
The fire could be at 0 ft. Repeat reverse engineering methodology
for steps 1. or 2. above, but now at 0 ft separation. Find what fire
breaks the window within 2 minutes.
Yes, people will in fact have time to... ' back away from the hot window,
Johnny. ´ Convert this critical fire
to gallons of Jet A1 fuel, and ask ourselves, 'Selves, what is the
likelihood that we are going to have
a fire of xxx gallons of Jet A1 from a spill at 0 ft from the window?´ If
in our gut of guts, in our
firefighting experience, in our common sense, we feel and rationally know
that xxx gallons of
Jet A1 is not going to be reasonably spilled at 0 ft from the window, then
we let the prescription
for the window sprinklers go. We do not have to repeat this process for
distances further from the
building, UNTIL we come to a distance where there IS a chance MORE than xxx
gallons of fuel
could be spilled (e.g. fuel tanks in the aircraft wings). Repeat the
analysis for each location where a
larger spill is possible, calculate the amount of Jet A1 needed to create
the critical fire at this
distance, and repeat the process of asking the risk assessment machines
(i.e. Engineer and Fire Authority)
to evaluate the probability of that spill ever occuring (ignoring that not
all spills ignite, and that drainage
will be taking fuel away from most windows, and that batch spill fires last
about 3 minutes).
We can follow the NFPA 415 prescriptions, or we can use the alternative
methods and materials
leveraged with common sense and logic. Sooner rather than later, we will
have brave Fire Authorities
and Engineers rationally agree on accepting the risk of ignoring
parts-of-prescriptive-mitigations-
that-yield-large-profits-for-vendors, when the odds of the prescription ever
being needed is
extremely unlikely at best.
Of the small handful of occupancy types where prescriptive fire standards
have a relatively tough time in achieving reasonable fire performance,
airports are near the top of
this short list. Engineers and Fire Authorities should be open minded,
rational and favorable in considering
performance-based designs that increase reliability (e.g. 1]. gravity
rarely fails to drain liquid
downslope; there are exceptions and icedams are one of them, 2]. there are
very few fuel spill points of
sufficient volume that are close enough to concourse glazing to break that
glazing from fire exposure)
while decreasing cost and construction time.
scot deal
excelsior fire engineering
p.s. Greg, after invoking the 100 ft rule from NFPA 415, consider bowsers
CAN drop 30,000 Liters,
but if you are using a fuel-hydrant system, they are often redundantly safe
regarding spills, so in
case of fuel-hydrant systems, we would be looking at a leak from the
airplane fuel tanks...
--previous message ----------
On Tue, Feb 9, 2010 at 14:09, Greg McGahan <[email protected]> wrote:
> I need help before I make a mistake and insult a PE. Does anyone have
> recent experience in this area that can help with a few questions:
>
> 1) The Severity of the exposure per 80A
> 2) The meaning of the requirement to calculate ANY 300' section - I assume
> - but does it indeed mean even if there are multiple deluge systems on one
> side of the concourse that you must calculate 300 feet regardless so you
> would have multiple systems flowing in their entirety?
>
>
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