Access holes or combination access hole/inlets should be placed at changes in direction, junctions of pipe runs, at intervals in long pipe runs, or wherever necessary for clean-out and inspection purposes. The table below provides maximum spacing criteria for access holes.

Table 10-3. Access Hole Maximum Spacing

Pipe Diameter	Maximum Distance
in.	ft.
12 - 24	300
27 - 36	375
39 - 54	450
> 60	900

It is possible to reduce head losses caused by turbulence within an access hole by rounding the flowline (bottom) of the access hole to match the flowlines of the pipes attached to the manhole. See for more details. For manholes larger than the incoming or outgoing pipes, expansion losses can sometimes be significant. Access holes that include other functions must be detailed to include facilities that will serve all the intended functions.

If the hydraulic grade line could rise above the access hole cover, the cover must be secured by bolting or with a locking mechanism to prevent removal by vandals or by a “blowout.” A “blowout” is caused when the hydraulic grade line rises higher than the access hole cover, which may force the cover to explode off.