Ventilation of Confined Spaces

Confined Space VentilationConfined spaces are not normally designed for convenient ventilationMust take steps to:ensure air is breathable before entering confined spacemaintain acceptable air quality in the confined space during entry

Hotwork in Confined SpacesPresents additional ventilation challenges in confined spacesIncludes torch cutting, welding, brazing and soldering, arch gouging

Hotwork in Confined SpacesRemember confined spaces concentrate hazards!Hotwork can create atmospheric hazards in confined spaces from fumes, gasses and vaporsEffective ventilation sometimes may only be accomplished by mechanical ventilation

Natural Ventilation in Confined SpacesChimney Effectconvection process created by temperature changes Occurs by sunlight heating vessel walls and air withinIf there is an opening in bottom and top of vessel, upward draft created

Natural Ventilation ProblemsConfined spaces rarely experience uniform thermal conditionsVarious sources of heat in confined spaceshuman bodieslightinghotwork processes

Natural Ventilation ProblemsFactors such as sunlight, body heat, lighting and hotwork are usually not sufficient to move enough air to provide an acceptable atmosphere

Overcoming Natural Ventilation ProblemsMust establish techniques and procedures to provide adequate ventilation

It is easier to work with than against natural convection.

Use of Mechanical VentilationProperly installed, can reduce or eliminate respiratory protection requirementsEffective engineering controls usually less dependent on worker attention than respiratory protection

29 CFR 1910.134

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

When is ventilation necessary?If atmosphere: contains insufficient oxygen or is oxygen richcontains flammable dusts or vaporscontains hazardous or toxic vapors, mists, fumes, gases, or fibers

When is ventilation necessary?If atmosphere: is subject to activities that may generate hazardous mists, vapors, fumes or gases, or may create either an oxygen deficiency or oxygen excess, andincreases heat stress on workers to unacceptable levels

CAUTIONSMany people resist wearing PPE, including respiratory protectionTangle of supplied air hoses in vessel with many welders can present a hazard

Ventilation- 29 CFR 1910.252(c)Spaces that require ventilationwork space less than 16 feet highvolume less than 10,000 cubic feet per welderwork areas with partitions, structural barriers, or other barriers that significantly obstruct airflow

Ventilation- 29 CFR 1910.252Ventilation options:provide at least 2000 cfm of airflow for each active welder; orprovide each welder with a local exhaust devicelocal exhaust devices must be capable of maintaining a velocity of 100 fpm toward the air intake

Ventilation Requirements29 CFR 1910.252 and 29 CFR 1926.353 require use of local exhaust ventilation or supplied air respiratory protection when performing hotwork using certain substances

Ventilation RequirementsFluorine compoundsZincLeadCadmiumMercuryBeryllium (local exhaust and supplied air respirators are required)

Ventilation RequirementsConstruction :chromiumstainless steels (if using MIG processes)

Air Moving DevicesTwo types:FansVenturi-type eductorsCan be air, steam or electrically driven

EductorsSometimes called air hornsAir powered and rely on venturi effects to move air

Criteria for Rating Air MoversFree Air DeliveryEffective Blower CapacityQuantity of air and air pressure required (air-driven devices)Electrical power requirements (electrically driven devices)

Factors Reducing PerformanceEquipment components in confined space Maintenance/construction materials erected in space Obstructions in make-up air manway Insufficient number of make-up air manways

Factors Reducing PerformanceMore restrictions to overcome = less air moved Air moving into space equals amount of air leaving the space

Air Driven Devices- Poor PerformanceReduced pressure and volume to air driven devices from multiple usersExcessively long air hoses

Increasing PerformanceSupplemental air compressors dedicated to air mover use (air driven devices)Supplemental air compressors connected directly to plant air systemEliminate short-circuiting of airflow

Designing Ventilation SystemsConfiguration, contents and tasks determine type of ventilationopening configurationproperties of expected atmospheric hazardstype of work being performed

Electrically Driven Centrifugal FansDesigned to overcome higher static pressuresUsually heavier than air-driven equipmentCan be used remotely to reduce noiseDue to power, can suck up debris

Local ExhaustSingle manway vesselsInterior obstructions that create dead spotsLack of feasible way to attach air-moving deviceWork with toxic metals

Local ExhaustEffective only when it captures and removes welding fumes and gasses at the source as they are emitted100 fpm capture velocity at the source of fumes or gasses

Local Exhaust- ConsiderationsLong runs reduce airflowAirflow loss minimized by use of smooth ducting with large radius bendsRun flexible ducting as straight as possibleConsider using plenums for multiple weldersField test flow/personal air monitors

Make-up air qualityMechanical ventilation uses surrounding airMake sure the make-up air is not a source of airborne contaminants