Ventilation of Confined Ventilation of Confined SpacesSpaces

Confined Space VentilationConfined Space Ventilation Confined spaces are not normally Confined spaces are not normally

designed for convenient ventilationdesigned for convenient ventilation Must take steps to:Must take steps to:

• ensure air is breathable before ensure air is breathable before entering confined spaceentering confined space

• maintain acceptable air quality in the maintain acceptable air quality in the confined space during entryconfined space during entry

Hotwork in Confined Hotwork in Confined SpacesSpaces Presents additional ventilation Presents additional ventilation

challenges in confined spaceschallenges in confined spaces Includes torch cutting, welding, Includes torch cutting, welding,

brazing and soldering, arch brazing and soldering, arch gouginggouging

Hotwork in Confined Hotwork in Confined SpacesSpaces Remember… confined spaces Remember… confined spaces

concentrate hazards!concentrate hazards! Hotwork can create atmospheric Hotwork can create atmospheric

hazards in confined spaces from hazards in confined spaces from fumes, gasses and vaporsfumes, gasses and vapors

Effective ventilation sometimes may Effective ventilation sometimes may only be accomplished by only be accomplished by mechanical ventilationmechanical ventilation

Natural Ventilation in Natural Ventilation in Confined SpacesConfined Spaces ““Chimney Effect”Chimney Effect”

• convection process created by convection process created by temperature changes temperature changes

Occurs by sunlight heating vessel Occurs by sunlight heating vessel walls and air withinwalls and air within

If there is an opening in bottom and If there is an opening in bottom and top of vessel, upward draft createdtop of vessel, upward draft created

Natural Ventilation Natural Ventilation ProblemsProblems Confined spaces rarely experience Confined spaces rarely experience

uniform thermal conditionsuniform thermal conditions Various sources of heat in confined Various sources of heat in confined

spacesspaces• human bodieshuman bodies• lightinglighting• hotwork processeshotwork processes

Natural Ventilation Natural Ventilation ProblemsProblems Factors such as sunlight, body Factors such as sunlight, body

heat, lighting and hotwork are heat, lighting and hotwork are usually not sufficient to move usually not sufficient to move enough air to provide an enough air to provide an acceptable atmosphereacceptable atmosphere

Overcoming Natural Overcoming Natural Ventilation ProblemsVentilation Problems Must establish techniques and Must establish techniques and

procedures to provide adequate procedures to provide adequate ventilationventilation

It is easier to work It is easier to work withwith than than againstagainst natural convection. natural convection.

Use of Mechanical Use of Mechanical VentilationVentilation Properly installed, can reduce or Properly installed, can reduce or

eliminate respiratory protection eliminate respiratory protection requirementsrequirements

Effective engineering controls Effective engineering controls usually less dependent on worker usually less dependent on worker attention than respiratory attention than respiratory protectionprotection

29 CFR 1910.13429 CFR 1910.134

When feasible, effective When feasible, effective engineering controls must be used engineering controls must be used rather than respiratorsrather than respirators

When is ventilation When is ventilation necessary?necessary? If atmosphere: If atmosphere:

• contains insufficient oxygen or is contains insufficient oxygen or is oxygen richoxygen rich

• contains flammable dusts or vaporscontains flammable dusts or vapors• contains hazardous or toxic vapors, contains hazardous or toxic vapors,

mists, fumes, gases, or fibersmists, fumes, gases, or fibers

When is ventilation When is ventilation necessary?necessary? If atmosphere: If atmosphere:

• is subject to activities that may is subject to activities that may generate hazardous mists, vapors, generate hazardous mists, vapors, fumes or gases, or may create either fumes or gases, or may create either an oxygen deficiency or oxygen an oxygen deficiency or oxygen excess, andexcess, and

• increases heat stress on workers to increases heat stress on workers to unacceptable levelsunacceptable levels

CAUTIONSCAUTIONS Many people resist wearing PPE, Many people resist wearing PPE,

including respiratory protectionincluding respiratory protection Tangle of supplied air hoses in Tangle of supplied air hoses in

vessel with many welders can vessel with many welders can present a hazardpresent a hazard

Ventilation- 29 CFR Ventilation- 29 CFR 1910.252(c)1910.252(c) Spaces that require ventilationSpaces that require ventilation

• work space less than 16 feet highwork space less than 16 feet high• volume less than 10,000 cubic feet volume less than 10,000 cubic feet

per welderper welder• work areas with partitions, structural work areas with partitions, structural

barriers, or other barriers that barriers, or other barriers that significantly obstruct airflowsignificantly obstruct airflow

Ventilation- 29 CFR Ventilation- 29 CFR 1910.2521910.252 Ventilation options:Ventilation options:

• provide at least 2000 cfm of airflow provide at least 2000 cfm of airflow for each active welder; orfor each active welder; or

• provide each welder with a local provide each welder with a local exhaust deviceexhaust device– local exhaust devices must be capable of local exhaust devices must be capable of

maintaining a velocity of 100 fpm toward maintaining a velocity of 100 fpm toward the air intakethe air intake

Ventilation RequirementsVentilation Requirements 29 CFR 1910.252 and 29 CFR 29 CFR 1910.252 and 29 CFR

1926.353 require use of local 1926.353 require use of local exhaust ventilation or supplied air exhaust ventilation or supplied air respiratory protection when respiratory protection when performing hotwork using certain performing hotwork using certain substancessubstances

Ventilation RequirementsVentilation Requirements Fluorine compoundsFluorine compounds ZincZinc LeadLead CadmiumCadmium MercuryMercury Beryllium (local exhaust and supplied Beryllium (local exhaust and supplied

air respirators are required)air respirators are required)

Ventilation RequirementsVentilation Requirements Construction :Construction :

• chromiumchromium• stainless steels (if using MIG stainless steels (if using MIG

processes)processes)

Air Moving DevicesAir Moving Devices Two types:Two types:

• FansFans• Venturi-type eductorsVenturi-type eductors

Can be air, steam or electrically Can be air, steam or electrically drivendriven

EductorsEductors Sometimes called “air horns”Sometimes called “air horns” Air powered and rely on venturi Air powered and rely on venturi

effects to move aireffects to move air

Criteria for Rating Air Criteria for Rating Air MoversMovers Free Air DeliveryFree Air Delivery Effective Blower CapacityEffective Blower Capacity Quantity of air and air pressure Quantity of air and air pressure

required (air-driven devices)required (air-driven devices) Electrical power requirements Electrical power requirements

(electrically driven devices)(electrically driven devices)

Factors Reducing Factors Reducing PerformancePerformance Equipment components in confined Equipment components in confined

space space Maintenance/construction materials Maintenance/construction materials

erected in space erected in space Obstructions in make-up air manway Obstructions in make-up air manway Insufficient number of make-up air Insufficient number of make-up air

manwaysmanways

Factors Reducing Factors Reducing PerformancePerformance More restrictions to overcome = More restrictions to overcome =

less air moved less air moved Air moving into space equals Air moving into space equals

amount of air leaving the spaceamount of air leaving the space

Air Driven Devices- Air Driven Devices- Poor PerformancePoor Performance Reduced pressure and volume to Reduced pressure and volume to

air driven devices from multiple air driven devices from multiple usersusers

Excessively long air hosesExcessively long air hoses

Increasing PerformanceIncreasing Performance Supplemental air compressors Supplemental air compressors

dedicated to air mover use (air dedicated to air mover use (air driven devices)driven devices)

Supplemental air compressors Supplemental air compressors connected directly to plant air connected directly to plant air systemsystem

Eliminate “short-circuiting” of Eliminate “short-circuiting” of airflowairflow

Designing Ventilation Designing Ventilation SystemsSystems Configuration, contents and tasks Configuration, contents and tasks

determine type of ventilationdetermine type of ventilation• opening configurationopening configuration• properties of expected atmospheric properties of expected atmospheric

hazardshazards• type of work being performedtype of work being performed

Electrically Driven Centrifugal Electrically Driven Centrifugal FansFans Designed to overcome higher Designed to overcome higher

static pressuresstatic pressures Usually heavier than air-driven Usually heavier than air-driven

equipmentequipment Can be used remotely to reduce Can be used remotely to reduce

noisenoise Due to power, can suck up debrisDue to power, can suck up debris

Local ExhaustLocal Exhaust Single manway vesselsSingle manway vessels Interior obstructions that create Interior obstructions that create

“dead spots”“dead spots” Lack of feasible way to attach air-Lack of feasible way to attach air-

moving devicemoving device Work with toxic metalsWork with toxic metals

Local ExhaustLocal Exhaust Effective only when it captures and Effective only when it captures and

removes welding fumes and removes welding fumes and gasses at the source as they are gasses at the source as they are emittedemitted

100 fpm capture velocity at the 100 fpm capture velocity at the source of fumes or gassessource of fumes or gasses

Local Exhaust- Local Exhaust- ConsiderationsConsiderations Long runs reduce airflowLong runs reduce airflow Airflow loss minimized by use of Airflow loss minimized by use of

smooth ducting with large radius bendssmooth ducting with large radius bends Run flexible ducting as straight as Run flexible ducting as straight as

possiblepossible Consider using plenums for multiple Consider using plenums for multiple

welderswelders Field test flow/personal air monitorsField test flow/personal air monitors

Make-up air qualityMake-up air quality Mechanical ventilation uses Mechanical ventilation uses

surrounding airsurrounding air Make sure the make-up air is not a Make sure the make-up air is not a

source of airborne contaminantssource of airborne contaminants