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

• xygen 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,
• r 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

• f airborne contaminants