Ventilation of Confined Spaces Confined Space Ventilation Confined - PowerPoint PPT Presentation

Ventilation of Confined Spaces

Confined Space Ventilation  Confined spaces are not normally designed for convenient ventilation  Must take steps to: • ensure air is breathable before entering confined space • maintain acceptable air quality in the confined space during entry

Hotwork in Confined Spaces  Presents additional ventilation challenges in confined spaces  Includes torch cutting, welding, brazing and soldering, arch gouging

Hotwork in Confined Spaces  Remember… confined spaces concentrate hazards!  Hotwork can create atmospheric hazards in confined spaces from fumes, gasses and vapors  E ffective ventilation sometimes may only be accomplished by mechanical ventilation

Natural Ventilation in Confined Spaces  “Chimney E ffect” • convection process created by temperature changes  Occurs by sunlight heating vessel walls and air within  If there is an opening in bottom and top of vessel, upward draft created

Natural Ventilation Problems  Confined spaces rarely experience uniform thermal conditions  Various sources of heat in confined spaces • human bodies • lighting • hotwork processes

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

Overcoming Natural Ventilation Problems  Must establish techniques and procedures to provide adequate ventilation  It is easier to work with than against natural convection.

Use of Mechanical Ventilation  Properly installed, can reduce or eliminate respiratory protection requirements  E ffective 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 rich • contains flammable dusts or vapors • contains 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, and • increases heat stress on workers to unacceptable levels

CAUTIONS  Many people resist wearing PPE , including respiratory protection  Tangle of supplied air hoses in vessel with many welders can present a hazard

Ventilation- 29 CFR 1910.252(c)  Spaces that require ventilation • work space less than 16 feet high • volume less than 10,000 cubic feet per welder • work areas with partitions, structural barriers, or other barriers that significantly obstruct airflow

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

Ventilation Requirements  29 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 Requirements  Fluorine compounds  Zinc  Lead  Cadmium  Mercury  Beryllium (local exhaust and supplied air respirators are required)

Ventilation Requirements  Construction : • chromium • stainless steels (if using MIG processes)

Air Moving Devices  Two types: • Fans • Venturi-type eductors  Can be air, steam or electrically driven

E ductors  Sometimes called “air horns”  Air powered and rely on venturi effects to move air

Criteria for Rating Air Movers  Free Air Delivery  E ffective Blower Capacity  Quantity of air and air pressure required (air-driven devices)  E lectrical power requirements (electrically driven devices)

Factors Reducing Performance  E quipment 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 Performance  More restrictions to overcome = less air moved  Air moving into space equals amount of air leaving the space

Air Driven Devices- Poor Performance  Reduced pressure and volume to air driven devices from multiple users  E xcessively long air hoses

Increasing Performance  Supplemental air compressors dedicated to air mover use (air driven devices)  Supplemental air compressors connected directly to plant air system  E liminate “short-circuiting” of airflow

Designing Ventilation Systems  Configuration, contents and tasks determine type of ventilation • opening configuration • properties of expected atmospheric hazards • type of work being performed

E lectrically Driven Centrifugal Fans  Designed to overcome higher static pressures  Usually heavier than air-driven equipment  Can be used remotely to reduce noise  Due to power, can suck up debris

Local E xhaust  Single manway vessels  Interior obstructions that create “dead spots”  Lack of feasible way to attach air-moving device  Work with toxic metals

Local E xhaust  E ffective only when it captures and removes welding fumes and gasses at the source as they are emitted  100 fpm capture velocity at the source of fumes or gasses

Local E xhaust- Considerations  Long runs reduce airflow  Airflow loss minimized by use of smooth ducting with large radius bends  Run flexible ducting as straight as possible  Consider using plenums for multiple welders  Field test flow/ personal air monitors

Make-up air quality  Mechanical ventilation uses surrounding air  Make sure the make-up air is not a source of airborne contaminants