×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

NFPA 820 Wet Well Ventilation - Dry Volume or Air Space Above Liquid?

NFPA 820 Wet Well Ventilation - Dry Volume or Air Space Above Liquid?

NFPA 820 Wet Well Ventilation - Dry Volume or Air Space Above Liquid?

(OP)
There is a fairly large wet well that I will need to ventilate per NFPA 820, 12 ACH to classify it as class 1 div 2. We also need to provide odour control to the exhaust air, so that resulted in a huge odour control unit.

NFPA 820 stated 12 ACH is required, but can we get away with only calculating the air space above the liquid, when the wet well has liquid? I would assume that if the wet well is dry, there is little to none H2S production. I would also assume the H2S production is proportional to the amount of liquid (sewage) in the wet well, but the air space is inversely proportional to the amount of liquid in the wet well. So what is the best way to determine the ACH required?

RE: NFPA 820 Wet Well Ventilation - Dry Volume or Air Space Above Liquid?

VFD pumps are commonly specified in order to use a smaller wet well. With that pumping arrangement, the volume of water is normally constant. It seems reasonable to use the volume above the water level as you are proposing.

RE: NFPA 820 Wet Well Ventilation - Dry Volume or Air Space Above Liquid?

H2S generation is difficult to predict as it depends on what the wastewater is made up of. A pumpstation at capacity is more likely to have low odour/H2S issues than a new pumpstation designed for a development that will be completely occupied in 10 years

a wetwell will never be dry as the pumps will shut off at a certain depth, so there will be wastewater sitting in the base festering and producing H2S

Also unless your odour unit is active ie. with an extractor fan, the flow to the odour unit will be maximum as the wetwell goes from empty to full.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login



News


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close