the safety of personnel in temporary buildings during ... during plant start-up john henderson,...

Engineering Solutions . . . Delivering Results

The safety of personnel in temporary buildings The safety of personnel in temporary buildings during plant startduring plant start--upup

John Henderson, Principal Safety Engineer, CB&I LummusJohn Henderson, Principal Safety Engineer, CB&I Lummus

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Introduction to CB&IIntroduction to CB&I

Chicago Bridge & Iron Company N.V.

CB&I Lummus CB&I Steel PlateStructures

LummusTechnology

• Upstream• Offshore• LNG Liquefaction• LNG Regasification• Gas Processing• Pipelines• U/G Gas Storage

• Downstream• Refining• Petrochemical

• Low Temperature Storage• Floating Roof Tanks• Flat Bottom Tanks• Water• Nuclear Containment• Cryogenic Spheres

• Clean Fuels• Hydrocracking• Hydrotreating• FCC• Visbreaking• CLG• CDTECH• Randall Gas• Sulphur• Hydrogen

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Integrated Technology and EPFC ContractorIntegrated Technology and EPFC Contractor

Engineering Procurement Technology Fabrication

Introduction to CB&IIntroduction to CB&I

Construction MechanicalInstallation

Operator Training

Start-up and Commissioning


Structure of the presentationStructure of the presentation

•• Description of the issue.Description of the issue.•• The Texas City incident The Texas City incident –– a turning point.a turning point.•• Development of new codes, guidelines and Development of new codes, guidelines and

improved consequence modelling.improved consequence modelling.•• CB&ICB&I’’s assessment process.s assessment process.•• Typical mitigation measures for buildings.Typical mitigation measures for buildings.•• An example of detailed analysis.An example of detailed analysis.•• Summary of key recommendations.Summary of key recommendations.

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Expansion of LNG terminal Expansion of LNG terminal

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Typical temporary buildings and hazardTypical temporary buildings and hazard

Pipeline valves

Timber framed cabins

Steel framed cabins with

steel window shutters

Steel clad

cabins

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Significant Hazards Significant Hazards

•• Explosions (require congestion or confinement)Explosions (require congestion or confinement)– Building collapse– Building components become projectiles (e.g. glass,

wall panels)

•• Flammable gas cloudsFlammable gas clouds– Flash fire (short duration)

• Failure of doors/windows – flame penetration• Direct radiation exposure via windows

– High dose to personnel– Secondary internal fires

– Internal explosion

•• Heat (thermal radiation) from jet or pool firesHeat (thermal radiation) from jet or pool fires•• (Toxic gas clouds)(Toxic gas clouds)

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Explosion damage to temporary buildingsExplosion damage to temporary buildings

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Explosion damage: lightwood cabinExplosion damage: lightwood cabin

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Explosion damage: local control roomExplosion damage: local control room

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•• Publication of API RP 753Publication of API RP 753• ‘Management of Hazards Associated with Location of

Process Plant Portable Buildings’ June 2007.

•• Industry initiatives such as those by FABIG (Fire Industry initiatives such as those by FABIG (Fire and Blast Industry Group)and Blast Industry Group)

•• Buildings with fire and blast rating for special Buildings with fire and blast rating for special applications such as maintenance of live plant.applications such as maintenance of live plant.

•• Use of CFD (computational fluid dynamics) models: Use of CFD (computational fluid dynamics) models: • predict explosion and fire consequences more accurately.

•• Use of QRA (quantitative risk analysis):Use of QRA (quantitative risk analysis):• determines the probability of a hazard occurring and the

consequent probability of fatalities in a particular location.

Developments since 2005Developments since 2005

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•• Consider temp buildings early in the project cycleConsider temp buildings early in the project cycle• Part of construction / contract planning• Process safety (fire & explosion) assessments available.• Identify temp building requirements and obtain building

data.• If possible, locate temp buildings in same areas as

permanent buildings.

•• Hazard identificationHazard identification• Identify the hazards, area-by-area, using plant layouts and

fire & explosion assessments produced at the design stage. Compare the hazards to the building locations.

•• Evacuation PlanEvacuation Plan• Cannot rely on evacuation as hazards may develop

quickly and present dilemmas.

Assessment processAssessment process--11

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•• Review the guidance availableReview the guidance available• API RP 753• Guidance for the location and design of..buildings,

appendix 5 (Chemical Industries Association)• Baker Report on Texas City

•• Define the Define the ‘‘design scenariosdesign scenarios’’ for assessing each for assessing each building or group of buildingsbuilding or group of buildings• Explosions• Gas dispersion / flash fires• Jet or pool fires• Obtain safety assessment /consequence model for each

scenario.

Assessment processAssessment process-- 22

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Explosion modelling Explosion modelling -- 11

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Blast Overpressure Decay

0.000

0.050

0.100

0.150

0.200

0.250

0 250 500 750 1000 1250 1500

Distance from centre of confined volume (m)

Stat

ic O

verp

ress

ure

(bar

g)

Material : Methane


Explosion modelling Explosion modelling -- 22

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Example of computational fluid dynamic modelling of an explosion within a structure


•• Decide on simple criteria (limits) or a riskDecide on simple criteria (limits) or a risk--based based approach. approach. • Simple criteria, e.g. API codes – RP 753 and RP 521• Risk based – probability of the design scenario combined

with impact analysis, occupancy of building, and chance of survival to give overall risk that can be compared with standard criteria, e.g. probability of individual fatality of less than 1 in 10000 per year.

Assessment processAssessment process-- 33

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Use of API RP 753Use of API RP 753

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•• Examples of simple criteria applied to a Examples of simple criteria applied to a ‘‘light wood light wood trailertrailer’’::• Explosion: API RP 753 – zonal approach

• <40 mbar unrestricted; >60 mbar unacceptable• Between 40 – 60 mbar a detailed assessment is required.

• Gas cloud gas concentration above 0.5 LFL unacceptable.• Fire: API RP 521

• Thermal radiation above 6.3 or 9 kW/m2 (depending on evacuation time) is unacceptable.

•• Predict the impact for each building or group of Predict the impact for each building or group of buildingsbuildings• Compare consequence model to criteria.• Detailed structural assessment may be necessary.• Mitigation (other than relocation) may be possible.• Care needed when simple criteria appear met.

Assessment process Assessment process –– 44

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•• Depending on the consequences, classify each Depending on the consequences, classify each building or group of buildings:building or group of buildings:• Class 0: the building can be closed-down and taken off the

site before commissioning.• Class 1: the building can be retained in its location without

any changes to design or function.• Class 2: the building cannot stay in its location without

mitigation measures or changing its function.• Class 3: the building cannot stay in its current location• The number of people in the building may affect its

classification.

Assessment process Assessment process -- 55

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•• Typical mitigation measures for buildings in class 2:Typical mitigation measures for buildings in class 2:– Signed escape routes with adequate lighting routed away

from hazards to clearly marked muster areas.– Check if site gas and fire alarms are audible / visible –

consider additional.– Architectural features: no heavy equipment on roof (a/c),

protective films / shutters on windows, emergency exits on side away from hazard, structural stiffening.

– Position unoccupied buildings as barrier.– Demount any stacked container type.

Typical mitigation measuresTypical mitigation measures

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•• Consider a large building approx 250m from a gas Consider a large building approx 250m from a gas compressor building.compressor building.

•• Building 33 m x 24 m x 3 mBuilding 33 m x 24 m x 3 m•• 25 kitchen staff present 10 hours/day25 kitchen staff present 10 hours/day•• 275 construction workers present 2 hours/day275 construction workers present 2 hours/day

Detailed assessment of a large buildingDetailed assessment of a large building

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Typical large temporary buildingTypical large temporary building

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Detailed assessment of a large buildingDetailed assessment of a large building

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•• Impact and consequence assessmentImpact and consequence assessment• Risk due to gas compressor building located approx 250m

away.• 40 mbar overpressure occurs at a frequency of between 1

and 3 x 10-4 per year.• Building analysis predicts collapse at about 20 mbar

• Large modular building not designed for non-normal loads• Construction plan modified to relocate building prior to

commissioning.

Detailed assessment of large buildingDetailed assessment of large building

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• Do assessment and planning as early as practical in the project cycle. Several teams are involved: HSE, Safety Engineering, Construction and Project Management.

• Consider all hazard types and analyze the impacts.• As far as practical, administrative and back-up staff should

be excluded from buildings within hazard ranges.• Use prescriptive guidelines critically and be prepared to

modify or use more sophisticated techniques, especially where large numbers of people involved.

• Where it’s acceptable to maintain buildings in position through commissioning, ensure reasonable mitigation measures are taken to reduce the risk.

Key recommendationsKey recommendations

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Expect the unexpectedExpect the unexpected

The way incidents develop is difficult to predict, so try to have some contingency in plans and designs.

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the safety of personnel in temporary buildings during ... during plant start-up john henderson,...

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