ADVANCED FIRE FIGHTING

FTOPS2 korytarl@yahoo.ca

LPG - LNG HAZARDS AND CONTROL

3/4/2015 2

INTRODUCTION

Liquid Petroleum Gas (LPG) and Liquefied Natural Gas (LNG) are

petroleum products which are quite safe when contained in their

storage containers.

Released into the atmosphere they condense the moisture in the air

producing vapor clouds these vapor clouds pose a serious hazard to

the safety of personnel and plant alike should they be ignite.

Knowing how to properly respond to releases of LNG and LPG products

can make the difference between a small leak or a catastrophic event

which kills many people and destroys property.

No LPG - LNG release should be considered a minor event. The

potential for it to rapidly escalate into a catastrophe is ever present.

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LPG - LNG COMPOSITION

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LPG CHARACTERISTICS

LPG is predominantly a mixture of propane and butane in a liquid state

at room temperatures when under moderate pressures of less than

200 psig.

LPG is:

Colourless

Odourless

Non-Corrosive

Specific Gravity (H2O = 1) 0.60

Vapor Density (Air = 1) 1.92

A gas at atmospheric pressure

Boils at -42.1 C

Flammable (2.1 % - 9.5 %)

Auto ignition temp 450 0 C

0.307 mill joule ignition temp

Expansion ratio of 275:1

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LNG CHARACTERISTICS

LNG is made up mostly of methane. The liquefaction process removes

the non-methane components like carbon dioxide, water, mercury,

H2S, propane, butane, ethane from the natural gas.

LNG is:

Colourless

Odourless

Non-corrosive

Lighter then air (> -1070 C)

Specific Gravity (H2O = 1) 0.42

Vapor Density (Air = 1) 0.47

A gas at atmospheric pressure

Boils at – 1620 C

Flammable (range 5% to 15%)

Auto ignition temp 537 0 C

0.29 mill joule ignition temp *

Expansion ratio of 600:1

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MAJOR EVENT CONSEQUENCES

There are numerous conditions which can result in a leak of flammable

vapors any of which can result in unwanted events.

The main consequences to be aware of are:

Unconfined vapor clouds resulting in flash fires (LNG)

Unconfined vapor cloud explosions (Propane, Ethane)

Pools of liquid products resulting in pool fires

Confined vapor clouds and resulting vapor cloud explosions (VCE)

Spill containment basin and trench fires

Pressurized leaks and resultant jet fires

Boiling Liquid Expanding Vapor Explosion (BLEVE)

Secondary events to be aware of:

Metal failure due to brittle effect

Direct flame contact

Radian heat

Blast overpressures

Fragmentation impact

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MAJOR HAZARDS

In addition to the most obvious hazards that come with a flammable

gas . When we combine LPG characteristics we realize a situation can

quickly become much more complicated and dangerous.

The key points to consider and remember are:

Cryogenic injuries

Metal failure due to brittle effect

Large leaks develop large vapor clouds

Vapor clouds will travel down wind, possibly to an ignition source

LPG Vapor clouds explode (UVCE), unconfined LNG clouds do not

Obstructions reduce cloud spread but increase blast overpressures

It takes little energy to ignite LPG/LNG vapors

LNG gas fires are 2 times hotter then any other hydrocarbon fire

Jet fires can cause adjacent supports, pipes and vessels to fail

When subjected to fire, pressurized vessels can BLEVE

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CONGESTION vs OVERPRESSURE

The effect of congestion on the propagation of explosions is well

known. The following gives a clearer picture of the effects of

congested plant areas and the respective explosion overpressures

that can be generated.

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THE GOOD NEWS

LNG is safer then Propane, Ethane, Butane, etc.

The key points to remember are:

Natural gas is less reactive than other fuels and potential plant

explosions are less severe than with, say, hydrogen, propane or

ethylene.

Detonations of natural gas/air mixtures in the open are not considered

to be credible design accidental events, because of the restrictive

conditions under which they could happen.

Rapid Phase Transition explosion phenomenon are confined to rich

LNG not lean LNG which lacks the heavy ends that are involved in the

development of the explosion such as Propane and Ethane.

Unconfined RPT are not considered hazardous since they are less

energetic then combustion explosions. RPT

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FLAME SPEED vs OVERPRESSURES

In an accidental situation, we can expect that hydrogen and ethylene

will give higher explosion pressures than fuels like propane and

methane for the same size of gas cloud and with other conditions

being similar as well.

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CONTROL MEASURES

Two types of controls are considered to manage plant emergencies.

One at the design phase and the other in the operating phase.

Spill prevention

Spill detection

Spill minimization

Spill containment

Ignition control

Fire detection

Fire control

Exposure protection

DESIGN

Shutdown of the affected fire zone

Isolation of electrical equipment

Shutdown of ventilation systems

Isolation of ignition sources

By pass equipment

De-pressure equipment

Activation of fire protection systems

Evacuation of personnel

OPERATIONS

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DANGERS OF RADIANT HEAT

LNG pool fires burn between 150 kW/m2 to 340 kW/m2. The following

table should bring this information and impact on personnel safety into

perspective. Emissive power of a pool fire decreases with height (or

length along the axis).

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RADIANT HEAT RISKS

This simple graph demonstrates the effects of radiant heat on

personnel safety. Note that 5kW/m2 with a 10-15 second exposure

(clothed) time is considered the threshold for personnel exposure.

Heat emissions are the principal cause of damage from LNG fires,

capable of causing severe damage to personnel, structural steelwork,

plant and adjacent facilities if left unchecked.

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LNG FLAME CHARACTERISTICS

In the absence of wind an LNG pool fire column will burn upwards as

the burned gas rises with convection. The lower part or base of the

flame generates the most amount of heat. This heat diminishes with

height.

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VAPOUR CLOUD FLAMMABLE RANGE

LNG gas is flammable between 5% – 15 %. The LFL is normally found

outside the clouds visible boundary.

When an LNG vapor cloud disperses in an atmosphere of relative

humidity higher than 55 percent the entire flammable concentrations

are within the white, visible cloud

LNG IGNITION

Oxygen rich, too lean to burn

Explosive range

Fuel rich, too rich to burn

Wind direction

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WIND EFFECTS / FLAME TILT

When an LNG fire does occur its important to understand that wind has

a direct effect on the flame direction (tilt) and radiant heat affecting

adjacent equipment. (Note the absence of smoke)*

Rule of thumb: flame height is 2 to 2.5 times pool diameter.

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LARGE LNG FIRES

Unlike small LNG pool fires which burn smokeless. Large LNG pool

fires (> 20m dia.) burn with smoke.

The main effect of this condition is that the smoke of these fires reduces

the fires radiant heat. The cause is suspected to be the lack of sufficient

oxygen in the middle of the fire to complete the combustion cycle.

The reduced flame surface emissive power is due to the smoke .

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SHIP RELATED EVENTS

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LPG-LNG EVENT CONTROL

Responders are limited in the things they can do to manage vapor

cloud control and fire extinguishment . What they do however needs

to be done very quickly in order that the situation does not

escalate to a major event.

The following options exist:

Isolate the leak!!!!!!

Inject water to raise the level above the leak * (propane sphere)

Vapor dispersion with water curtain and or fog streams

Vapor control and dispersion with high expansion foam (HEF)

Fire intensity and radiant heat control with HEF

Exposure protection with cooling water streams

Fire extinguishment with dry chemical powder

Let the fire burn itself out!!!!!!

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VAPOUR DISPERSION

A major consideration in LNG releases is to prevent the vapor cloud

traveling to a source of ignition. An effective means of containing

and dispersing an LNG vapor cloud is to install flat fan water

curtains down wind of the vapor cloud.

As the cloud enters the water curtain it is heated resulting in its further

warming, evaporation and dispersion. The most effective tools are

monitors set at approximately 40 degrees which helps to entrain air

into the vapor cloud lowering its LFL.

(Water must not be allowed to run into the pool)*

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VAPOUR SUPPRESSION

Experience has shown that HEF is very effective in reducing LNG

flammable vapour concentrations at ground level during an LNG spill.

High-Expansion Foam Systems (HEF) provide vapour

suppression and dispersion by channelling the vapours upwards.

This same foam blanket reduces heat release and radiant heat

feedback on involved LNG pools allowing responders to approach for

extinguishment purposes.

LNG

500:1

LPG

300:1

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FIRE INTENSITY CONTROL

High expansion foam has been proven to reduce suppression vapors

as well as to reduce radiant heat levels by up to 60%.

A minimum of 1.8m of HEF foam needs to be applied to be

effective and maintained until all the vapors have evaporated. For this

purpose specialized TURBEX HEF generators are installed at spill

basins.

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EXTINGUISHMENT

Applying high volumes of dry chemical powder (DCP) is the only

way to extinguish a large LPG/LNG fire. Its important to use DCP’s

which are compatible with the HEF used to blanket the pool since it

can degrade the foam blanket quality.

LNG – DCP 1

Potassium bicarbonate or Monnex powders are widely used.

LNG – DCP 2

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UNIGNITED LPG/LNG STRATEGY

1. Perform SIZE UP and provide initial SITREP to command.

2. Evacuate personnel located downwind or downhill of the leak!!!

3. Isolate all sources of ignition down wind of the vapour cloud.

4. Establish exclusion zones (HOT, WARM, COLD)

5. Approach un-ignited liquid pools from an upwind direction.

6. Install water curtain sprays to confine / disperse gas clouds.

7. Blanket un-ignited LPG/LNG pools with HEF.

8. Top up foam blanket as required.

9. Be prepared to implement exposure protection.

10.Be prepared to implement fire extinguishment tactics with DCP.

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LPG/LNG FIRE STRATEGY

1. Perform SIZE UP and provide initial SITREP to command.

2. Evacuate – Rescue personnel.

3. Establish exclusion zones (HOT, WARM, COLD)

4. Where possible isolate the fuel supply!!!

5. Bypass and de-pressure the equipment.

6. Apply cooling water on vessel supports and skirts.

7. Apply cooling water on nearby pipelines and structures.

8. Water must be sprayed over the whole area of the vessel.

9. Replace hand lines with portable/trailer mounted monitors.

10.If relief valves open cooling must be increased.

11. If relief valves fail to close and the noise increases evacuate!!

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THANK YOU FOR YOUR ATTENTION!