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TABLE 14
EFFECT OF LEAKAGE DIAMETER AND DRAINAGE RATE ON THE FIRE SIZE OF FUEL TANKERS
Equivalent Calorific Power [MW (MBtu/hr)]
Diameter Leakage Mass Drainage Mass Flow of Fuel
of Leakage Flow of Fuel 0 kg/s 1 kg/s 2 kg/s 5 kg/s
[mm (in.)] [kg/s (lb/s)] (0 lb/s) (2.2 lb/s) (4.4 lb/s) (11 lb/s)
15 (0.6) 0.5 (1.1 lb/s) 22 (75) -- -- --
35 (1.4) 2.7 (6 lb/s) 120 (409.5) 76 (259) 33 (113) --
50 (1.9) 5.6 (12.3 lb/s) 245 (836) 201 (686) 158 (539) 27 (92)
Source: PIARC (21).
multiple HGV or bus accidents. Fire HRR, especially for vans section explores the emerging issues of alternative fuel
and heavy goods trucks, depend on the size of cargo load, vehicles on design fires.
which is usually unknown.
A risk analysis for the Oresund Tunnel (43) considers the Natural Gas and Liquid Gas Vehicles
possibility of fuel leakage from holes of 15, 35, and 50 mm
CNG and compressed biogas are primarily composed of
(0.6, 1.4, and 1.9 in.) equivalent diameter. These represent
methane, which is a gas lighter than air. Biogas can be clas-
the potential failure of small diameter fuel lines or a small
sified as a renewable natural gas. CNG is the more widely
amount of damage to a delivery hose flange. They do not rep-
used of the two. CNG is usually stored in a fuel tank at a pres-
resent the complete destruction of a delivery hose that would
sure of 200 to 250 bar (2900 to 3625 psi). The use of CNG is
give a hole diameter of 100 mm (3.9 in.). The leakage flow
depends on the diameter of the hole and the fluid pressure at increasing around the world and in 2008 there were more
the hole. For the holes considered, the mass flows are 0.5, than 9 million CNG vehicles and 13,000 refueling stations
2.7, and 5.6 kg/s (1.1, 6, and 12.3 lb/s), respectively. worldwide.
The drainage capacity of the drainage outlets is normally The situation with a CNG engine is more complicated
10 times greater. However, it was assumed that in an accident because the exhaust gas temperature from the CNG engine is
this could obstruct and limit the amount of drainage. The much higher (750°C or 1382°F) than from the diesel engine
calculations for the different fire scenarios gave calorific (450°C or 842°F). Additional measures can be considered
power outputs of between 22 MW (75 MBtu/hr) and 245 MW to reduce the risk of fire:
(836 MBtu/hr).
· Reduce the high exhaust temperature in the engine
Fire duration can be determined by the amount of available compartment by installing a water-cooled system. The
combustible material. The amount of fuel is different for each exhaust system must be made of noncorrosive special
study based on the type of vehicles, loads, and traffic patterns. steel with no leaks.
Tables 15 and 16 present several examples on design fire · Check the exhaust gas system for leaks and insulate as
scenarios in the Netherlands and France. needed.
· Provide a means of ventilation (additional louvers) in
the engine compartment for heat dissipation.
EXPLORING THE EMERGING ISSUES OF · Facilitate the removal of oil-contained contamination in
ALTERNATIVE FUEL VEHICLES ON DESIGN FIRES the engine and gear compartments.
· Install fire alarm sensors on busses.
Environmental issues such as climate change and scarcity
of resources have stimulated the development of new
energy carriers for vehicles. This also means that there will Hydrogen
be an increase in the number of vehicles running on these
new energy carriers in tunnels and other confined spaces. Hydrogen is a colorless, odorless, tasteless, nontoxic, non-
New energy carriers do not necessarily imply higher risks; corrosive gas approximately 14 times lighter than air. Much
however, they do represent a new situation with inherent research and development is currently focused on hydrogen
new risks, and such risks need to be considered and evaluated. and its feasibility as a vehicle fuel; however, in most cases
The mixture of different energy carriers, such as flammable only demonstration models are available (46). Hydrogen can
liquids, gases lighter than air, gases denser than air, batteries, be used either for internal combustion engine (ICE) vehicles
and so forth, can also constitute a risk itself, because there or fuel cell vehicles (FCVs). It is expected that after 2015,
are situations where different safety measures need to be fuel cells will be more common. There are several hydrogen
implemented depending on the energy carrier used and vehicle projects currently being tested. There is a Network of
the scenario in question. Some countries have restrictions Excellence called HySafe, which aims to safely introduce
on the use of some energy carriers in confined spaces. This hydrogen technologies and applications. This network has
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TABLE 15
DUTCH FIRE SCENARIOS FOR TUNNELS WITH LONGITUDINAL VENTILATION
IN RELATION TO HEAT RELEASE RATES
Heat
Release
Rate
(MW)
Size [MBtu/hr] Scenario Remarks
Small 6.1 [20.8] - A passenger car is completely burnt --
- Estimated duration of the fire: 25 min
- Smoke temperature less than 150°C (302°F) at a few meters
from the source of the fire
- Ventilation speed 1.5 m/s (295 fpm)
- Jet fans will only be impaired if they are right above the fire
- Fire fighting is possible from within a few meters of the
source of the fire
- Limited damage to the tunnel interior
- Limited amount of soot
Medium 100 [341] - A heavy goods vehicle loaded with wood is completely burnt Scenario
- The temperature of the fumes is about 800°C (1472°F) at a applicable
distance of 50 m (164 ft) from the source to Dutch tunnels
- Ventilation speed 1.5 m/s (295 fpm) in urban areas or
- Fire fighting is possible at a distance of 10 to 20 m (33 to 66 on secondary
ft) from the source of the fire when protective clothing is worn roads where the
- Damage to the tunnel interior, soot formation transport of
- Breakdown of jet fans at a distance of 150 to 300 m (492 to dangerous goods
984 ft) downstream of the fire is expected is forbidden
Large 300 - A tanker loaded with 50 m³ of gasoline is completely burnt Criterion
[1,024] - Estimated duration of the fire: 2 h for tunnels that
- Fire fighting is possible at a distance of from 10 to 20 m (33 to are opened to
66 ft) from the source when the ventilation speed is increased the transport of
to 3 m/s (591 fpm) and protective clothing is worn dangerous
- Use of water/foam should be considered goods (such as
- The temperature of the smoke will be about 1400°C (2552°F) propane or other
at a distance of about 20 m downstream of the fire toxic
- All jet fans will be damaged over a distance of 300 to 500 m substances)
(984 to 1,640 ft) downstream of the fire
- Considerable damage to the interior of the tunnel over a large
distance downstream of the fire; distance is increased when
the ventilation speed is increased
Source: Fire in Tunnels (9).
TABLE 16
FRENCH DESIGN FIRES WITH COMPLEMENTARY DATA FOR CFD CALCULATIONS
Clearance of the Tunnel
Height Height
Height >3.5 m >3.5 m
Height 2.7 m to 3.5 m (11.5 ft) (11.5 ft)
<2.7 m (8.9 ft to (no dangerous (dangerous
Parameter (8.9 ft) 11.5 ft) goods allowed) goods allowed)
Typical Fire 23 cars 1 van 1 HGV 1 fuel tanker
Heat Release Rate 8 [27] 15 [51] 30 [102] 200 [682]
(MW) [MBtu/hr]
Smoke Flow Rate 30 [1,059] 50 [1,766] 80 [2,825] 3001 [10,594]
(m3/s) [ft3/s]
Growth Time tg 5 5 10 10
(min)
Peak Duration tmax 20 30 60 60
(min)
Decline Time td 20 20 30 30
(min)
Released Energy 15 [14.2] 40 [37.9] 150 [142.1] 1000 [947.2]
(GJ) [MBtu]
Source: Fire in Tunnels (9).
1
In France, this smoke flow rate is generally not taken into account for the design of semi-transverse ventilation, even if
the transport of dangerous goods is allowed.
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led to a number of projects, including HyTunnel and InsHyde. circuit or an overcharge, and could result in a fire. The other
The goal of HyTunnel is to develop codes, standards, and is that the battery is exposed to an external risk, either some
regulations so that additional risks from the introduction of mechanical force or a thermal attack, as with a fire. There
hydrogen vehicles into tunnels can be handled safely. During have been instances of batteries exploding or releasing jet
the test period, no major safety-related incidents occurred to fires. There are some who believe that electric cars have been
the fuel cell buses. However, for the ICE buses there was one responsible for the larger number of fires when compared
unexpected release of hydrogen when a check valve within with nonelectric cars. This type of fire can also emit toxic fumes
the tank nozzle failed. from hydrogen fluoride and oxides of carbon, aluminum,
lithium, copper, and cobalt. The lithium salts used in the
The results indicated that owing to the nature of flame electrolyte contain fluorine or a chlorine compound, where
and fire development, tunnels with greater slopes and with hydrogen fluoride or hydrogen chloride can be produced
horseshoe cross sections (compared with equivalent rectan- during a fire.
gular cross sections) present lower hazards. In InsHyde, many
different aspects of hydrogen safety in confined spaces are There are some restrictions and regulations concerning the
evaluated and discussed, such as regulations, detection, use of alternative energy carriers, especially for compressed
ventilation, fire, and explosion. Both computer modeling and or liquefied gases. In relation to underground constructions,
experiments were performed to study different parameters most restrictions concern underground garages; however,
and effects. In that study, it was determined that among some also specifically address tunnels. Many of the restric-
hydrogen incidents the ignition source could not be identified tions can be related to LPG, which is also considered to be an
in 86% of the cases and was probably caused by spontaneous alternative fuel, together with liquefied natural gas (LNG),
ignition. However, in another research project, Wu (47) CNG, hydrogen, propane, methanol, ethanol, and biodiesel,
showed that conditions of oxygen deficit could be reached for in accordance with the U.S. Energy Policy Act of 2005. LPG
a higher release rate of hydrogen. This can lead to higher vehicles run on liquefied gas, which is denser than air.
temperature ceiling flows and damage to tunnel structures.
For hydrogen buses with internal combustion engines, these The following are examples of tunnels where LPG and
impacts also apply, and the installation of hydrogen sensors CNG are restricted (see Table 17):
is advisable.
· In Maryland, LPG is forbidden in the Baltimore Harbor
and Fort McHenry tunnels.
Batteries · LPG is forbidden in the Summer, Callahan, Prudential,
and Dewey Square tunnels in Massachusetts.
Electric cars that use batteries as an energy source are seen · LPG is forbidden in the Holland, Lincoln, Brooklyn
as the single most promising future energy carrier, in partic- Battery, and Queens Midtown tunnels in New York and
ular, for city traffic. One problem is the relatively short avail- New Jersey.
able driving distance before recharging is needed. Therefore, · In Virginia, an LPG ban covers the Chesapeake Bay
hybrid solutions are currently of greatest interest. In most Bridge tunnel.
cases a hybrid vehicle has both a conventional internal com- · In Italy, vehicles using LPG or gas are labeled before
bustion engine and an electric motor. There are also plug-in entering the Mont Blanc Tunnel or the Frejus Tunnel.
electric vehicles, with batteries that can be plugged in for · In France and the United Kingdom vehicles running on
charging, such as to house electricity, in addition to being gas are prohibited in the Euro Tunnel.
charged while running. · In Austria, LPG and CNG are not permitted in the Tauern
Tunnel.
Presently, nickel-metal-hydride batteries are the most
common used batteries in hybrid vehicles. These batteries are However, there are no restrictions on LPG vehicles in tunnels
robust, but have a relatively high self-discharge rate. Therefore, in Japan and many other countries.
for a variety of reasons, most interest is currently directed to
lithium-ion batteries. Lithium-ion batteries have a high energy Some examples of LPG fire incidents include:
density and a high cell voltage. In addition, the maintenance
need is low and there are no memory effects. However, to · A car crash in a highway tunnel near Palermo, Italy,
limit the peak voltage during charging for safe operation, a occurred on March 18, 1996. The accident involved a
protection circuit is built into each battery pack. This also tank truck transporting LPG, which caused propane to
limits the discharge current. Other safety features are also be released, which formed a burning gas cloud resulting
studied for lithium-ion batteries. in critical burns to 25 people. The subsequent boiling
liquid expanding vapor explosion (BLEVE) led to
Two main types of risks can occur with vehicle batteries. five fatalities. The cause of the accident was not strictly
One is that the battery (system) itself is the cause of the incident, the result of a new energy carrier, but it did involve a
such as with an electrical fault, which can be caused by a short vehicle transporting fuel for a new energy carrier.
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TABLE 17
SUMMARY OF KNOWN INCIDENTS INVOLVING CARS RUNNING ON LPG OR NEW ENERGY
CARRIERS (NOT ALL IN TUNNELS)
Type of No. of
Date Place Premises vehicles Fuel Ignition Consequences
Jan. 31, 1999 Venissieux, 1 LPG Arson Explosion;
France 6 fire fighters
severely injured
Sep. 2002 U.S. 1 CNG Car fire Rupture of
gas cylinder
Nov. 9, 2002 Seine-et- Garage 1 LPG Unknown Explosion;
Marne, building of origin
France collapsed; in
total 39 buildings
affected
Aug. 28, 2005 Firenze, San Donato LPG Engine Dense smoke
Italy tunnel fire
June 2006 Collatino, Parked on 1 LPG Arson Explosion,
Italy the street several cars,
2 garages, shops,
fire spread to
apartments
March 2007 Seattle, WA Row of 12 One with Arson 12 cars damaged
U.S. parked CNG or destroyed;
vehicles CNG tank
exploded when
fire fighters were
approaching;
debris approx.
30 m away
May 2007 Carson, Refueling 1 CNG Driver killed
CA, U.S.
Dec. 16, 2007 Salerno, Underground LPG Leakage Explosion;
Italy garage of gas one 3-storey
from building totally
vehicle destroyed;
5 other buildings
affected
June 7, 2008 U.S. Running on 1 Hybrid Short One burned-
the highway converted circuit out car
to plug-in
Sept. 19, Rovigno, Underground LPG Fire spread to
2008 Italy garage neighboring
garage and
threatened the
building
Oct. 2008 South Running on 1 LPG Lighting Explosion,
Yorkshire, the road of burns, broken
U.K. cigarette windows
Nov. 8, 2008 Mallaca, Filling 1 LPG Explosion of
Malaysia station vehicle;
passengers
severely injured
Dec. 28, 2008 Sampford Running on 1 LPG Unknown One burned-
Peverell, the highway out car
U.K.
Oct. 28, 2009 Marigliano, Parking 6 One with The cause Large explosion
Italy LPG of the damaged
initial fire vehicles and
unknown buildings
Source: Lönnermark (48).
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· On the night of January 31, 1999, a vehicle fuelled with Owing to the increase in pressure, the windows broke
LPG was set on fire by an arsonist in Vennissieux out- and the bonnet and the trunk blew opened. The driver
side Lyon, France. The LPG system was not equipped suffered minor burns to the face and body, but the seat
with a safety valve. This led to an increase in pressure absorbed most of the energy of the explosion, saving his
in the tank during the fire and the tank later exploded. life. The most likely explanation for the explosion was
Six firemen attempting to extinguish the fire were a leak in the tube between the filling valve and the tank.
severely injured. This incident led to action that could The car, which had been purchased second-hand three
help avoid this kind of incident in the future. Later, a weeks earlier, had been checked and approved twice at
requirement that such vehicles have safety valves was workshops.
introduced. · The most recent reported incident occurred on October
· On November 9, 2002, a vehicle fuelled with LPG began 28, 2009, in Marigliano, Italy. A fire started in a parked
to leak in a garage in Seineet-Marne in France. The high car running on a traditional fuel. It developed quickly and
density of the gas allowed it to spread over a large area spread to nearby vehicles. Six cars were ultimately
and down into the basement. At 11 p.m. the gas ignited, involved, including one using LPG, which quickly
an explosion occurred, and the building collapsed, exploded after catching on fire. The explosion damaged
burying several individuals, who were later saved. In cars in the vicinity and a nearby building. Debris from
total, the explosion affected 39 buildings within a radius the exploded car was found on the balcony of that build-
of 200 m. The roof of the LPG vehicle was found 150 m ing and windows were broken up to the eighth floor.
from the place where the vehicle had been parked. Stores at street level sustained severe damage.
· In June 2006, arsonists ignited an LPG-fuelled vehicle
in Collatino, Italy. The car was parked with other vehicles In addition to these car fires, some conclusions can be
on a street outside an apartment building. The fire started drawn from various bus fires. Three bus fires involving CNG
in the rear part of the vehicle, where the LPG tank was tanks are analyzed here. The first responders were unable to
positioned. The subsequent explosion of the tank led to extinguish these fires. The first conclusion was that the pressure
an intense fire, which ignited several other cars. The relief devices (PRDs) do not always release. This can happen
pressure wave destroyed two small garages and shops when there is local thermal exposure, such as from an imping-
located in the apartment building. The fire damaged the ing jet flame, which leads to insufficient heat for the PRD, or
façade and several balconies. it could be a malfunctioning heat release device. Either way
· In March 2007, an arsonist set fire to a row of vehicles it is important to minimize or eliminate areas with weaker
parked under a highway bridge in Seattle. The first fire protection, such as sun roofs, which could lead to such
responders were not aware that one of the cars was localized fire exposure. Another important issue is the time
CNG-fuelled. When they were 15 to 20 m (49.2 to 65.6 ft) necessary to completely empty the tank. In the incidents
from the burning vehicles the CNG tank exploded. The described, it would be preferable to have early PRD opening
fuel tank and other large pieces of debris landed about and fast emptying of the tank, although the situation could
30 m (98.4 ft) from the CNG vehicle. The fuel tank was be completely different if the buses had been located in
equipped with a safety valve, but exploded before the a confined environment such as a tunnel or underground
valve could release the pressure. garage. One main conclusion is that the safety of these types of
· In May 2007, a CNG tank in a vehicle in Carson, Cali- vehicles does not rely only on component tests. For example,
fornia, ruptured. The rupture occurred during refueling it is important to test the entire system, where the tanks and
and killed the driver. A day earlier, the driver had col- other components can be evaluated using relevant and realistic
lected the vehicle from a repair shop after a collision scenarios.
three weeks prior.
· In June 2008, a fire in a hybrid car converted to a plug-in The incidents summarized and described earlier are not
started while the car was running. The car used a lithium- meant to imply that all vehicles running on new energy
ion battery, which was partly damaged during the fire, carriers will explode when used or when exposed to fire.
but still provided power. According to the investiga- However, seeking the worst case scenarios is important when
tion, the most probable explanation of the incident was new energy carriers are developed. It is also important to
incorrect electrical wiring, which led to excessive heat realize that all risks are not eliminated by introducing PRDs.
generation. The heat destroyed some cells in the battery The outcome still depends on the design of these devices and
leading to a short circuit and the fire. on the fire scenario.
· In October 2008, a car running on LPG suddenly
exploded in South Yorkshire, United Kingdom. Remark- Wu of Sheffield University performed a CFD analysis
ably the driver survived and was able to describe the of hydrogen fires in tunnels. Hydrogen cars generate fast,
accident. He had recently refueled this car and was pro- high rising flames that quickly reach high temperatures (47).
ceeding slowly when he smelled gas. He had been told The body of the hydrogen car was not ignited and the flames
that this was normal after refueling. When he lit a ciga- lasted only a few minutes. It was concluded that a supercritical
rette the gas was ignited and filled the car with flames. velocity in the tunnel can completely eliminate the smoke
