1. Ventilation of Confined Spaces

2. 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

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

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

5. Natural Ventilation in Confined Spaces
“Chimney Effect”
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

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

7. 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

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

9. Use of Mechanical Ventilation
Properly installed, can reduce or eliminate respiratory protection requirements
Effective engineering controls usually less dependent on worker attention than respiratory protection

10. 29 CFR
When feasible, effective engineering controls must be used rather than respirators

11. 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

12. 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

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

14. 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

15. 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

16. Ventilation Requirements
29 CFR and 29 CFR require use of local exhaust ventilation or supplied air respiratory protection when performing hotwork using certain substances

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

18. Ventilation Requirements
Construction :
chromium
stainless steels (if using MIG processes)

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

20. Eductors Sometimes called “air horns”
Air powered and rely on venturi effects to move air

21. Criteria for Rating Air Movers
Free Air Delivery
Effective Blower Capacity
Quantity of air and air pressure required (air-driven devices)
Electrical power requirements (electrically driven devices)

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

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

24. Air Driven Devices- Poor Performance
Reduced pressure and volume to air driven devices from multiple users
Excessively long air hoses

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

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

27. Electrically 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

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

29. Local Exhaust
Effective 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

30. Local Exhaust- 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

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