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LPG LPG -- LNG HAZARDS AND CONTROLLNG HAZARDS AND CONTROL

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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 stateat room temperatures when under moderate pressures of less than 200 psig.

LPG is:

ColourlessOdourlessNon-CorrosiveSpecific Gravity (H2O = 1) 0.51Vapor Density (Air = 1) 1.92A gas at atmospheric pressureBoils at -42.1 CFlammable (2.1 % - 9.5 %)Auto ignition temp 450 0 C0.307 millijoule ignition tempExpansion 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-corrosiveLighter then air (> -1070 C)A gas at atmospheric pressureBoils at – 1620 CFlammable (range 5% to 15%)Auto ignition temp 537 0 C0.29 millijoule 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 firesConfined vapor clouds and resulting vapor cloud explosions (VCE)Spill containment basin and trench firesPressurized leaks and resultant jet firesBoiling Liquid Expanding Vapor Explosion (BLEVE)

Secondary events to be aware of:

Metal failure due to brittle effectDirect flame contactRadian heat Blast overpressuresFragmentation 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 effectLarge leaks develop large vapor cloudsVapor clouds will travel down wind, possibly to an ignition sourceLPG 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 vaporsLNG gas fires are 2 times hotter then any other hydrocarbon fireJet fires can cause adjacent supports, pipes and vessels to failWhen 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 overpressuresthat 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 richLNG 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 andmethane for the same size of gas cloud and with other conditionsbeing 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 preventionSpill detectionSpill minimizationSpill containmentIgnition controlFire detectionFire controlExposure protection

DESIGN

Shutdown of the affected fire zoneIsolation of electrical equipmentShutdown of ventilation systemsIsolation of ignition sourcesBy pass equipmentDe-pressure equipmentActivation of fire protection systemsEvacuation 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 rangeFuel 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 poolfires (> 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 vaporcloud 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 vaporsas 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 spillbasins.

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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’swhich 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!