Concrete Junction Box Design Criteria for Inside Height

[oengineer]

I am working on the design of a junction box connecting two RCBs. The RCBs are both 4x3. The flow is the same for both RCBs.

Due to the height of the entering & exiting RCBs, the I am calculating that the overall inside height (excluding top & bottom wall thickness) needs to be 4'-6".

Is there a criteria for Junction Boxes that states the minimum required inside height? Do workers typically enter inside junction boxes?

Any suggestions/ comments are appreciated.

 

[cvg]

unless this is a short culvert, open at the ends, than a 4 x 3 RCB will be virtually impossible to maintain, regardless how tall the manholes are. there is no efficient way to remove sediment or trash. it is too large to flush with water effectively and too small for entry. OSHA confined space regulations will restrict entry. some agencies (see example from city of phoenix below) require a minimum size which is much larger to provide more room for better maintenance and also to handle any reduced capacity due to accumulated sediment. you might consider making it bigger.

6.5.10 Box Culvert Dimensions
For maintenance purposes, minimum box culvert width shall be six feet and minimum height shall be six feet. Maximum desirable length shall be 200 feet.

https://www.phoenix.gov/streetssite/Documents/107171.pdf