Design, Operation, and Maintenance of LEV Systems for Hazardous Agents

This report provides a comprehensive overview of local exhaust ventilation (LEV) systems, crucial for controlling hazardous agents in various environments. The report delves into the core principles of ventilation systems, differentiating between general/dilution and local ventilation approaches, with a strong emphasis on the advantages and applications of LEV. It outlines the key design considerations for effective LEV systems, including the characteristics of contaminants, design principles of hoods, and the impact of enclosure design on capture velocity. The report also examines typical sources of contaminants and common problems associated with LEV systems. Furthermore, it highlights the importance of periodic inspection and maintenance, providing guidance and referencing relevant standards and manuals, such as those from ACGIH. The document concludes by summarizing key points influencing LEV performance and providing a selection of recommended designs, making it a valuable resource for anyone involved in designing, operating, or maintaining LEV systems.

 
LOCAL EXHAUST
VENTILATION (LEV)
SYSTEMS

Outline
 Ventilation systems approaches
 Main features
 Proper design considerations for local
ventilation
 Maintenance and inspection

Main types of Ventilation
General/Dilution
o Control of heat and/or contaminants removal
o Also called dilution ventilation
o Used in controlling contaminants only in cases local
exhaust cant work
o Uneconomical and ineffective
Local ventilation
o Traps contaminants at source
o Is a preferred control method because:
o more economical
o more effective

Local Exhaust Ventilation (LEV)
Characteristics of contaminants:
o particle speed
o source directionality
o gas/fume particles
o particle size
o temperature
o An ideal solution for one is impractical in another
o The solution has to be suited to source

Typical sources of contaminants

Typical sources of
contaminants

LEV: Design Principles of Hood
Key parameters influencing effective
operation
o Design of openings
o Distance for contaminant source
o Design of enclosure

Distance from source of contaminants

Velocity change with
time

Flow rate & Capture Velocity
 Flow is determined to provide the capture
velocity needed during design

Impact of enclosure design
Hood capture velocity having and without
flange
With flange Without flange

Impact of enclosure design
Airflow required to provide adequate
control
• Plain extract opening
• Enclosure added at
sides and above
bench
• Flange added at
rear
• Transparent screen
added at front
1m3/s
0.40m3/s
0.79m3/s
0.75m3/s