A contractor proposes to build a grease interceptor on site from cast-in-place concrete instead of installing a manufactured unit. Under the IPC, what governs whether that is acceptable?
- The interceptor must be of a type and capacity suited to the waste it will receive and must be approved by the code official
- BInterceptors built in the field are prohibited in every case, so only a listed manufactured unit may be set on a project like this one.
A flat prohibition on field-built interceptors does not exist, and large gravity interceptors are routinely poured in place. What the code insists on is a design suited to the waste plus approval.
- CAny concrete structure is acceptable as long as its liquid capacity is at least 750 gallons in total.
Capacity alone does not make an interceptor work. Baffling, retention time, inlet and outlet arrangement, venting and access all matter, and none of them follow from a gallon count.
- DNo approval is needed, because an interceptor is not considered a part of the drainage system proper.
An interceptor sits directly in the path of drainage and is regulated as part of the system. Treating it as outside the code would drop venting, access and material requirements too.
Why A is correct
The interceptor provisions require the device to be suited in type and capacity to the waste it receives and to be approved by the code official. That standard admits a properly designed job-built unit while still requiring the design, sizing basis and access details to be reviewed and accepted.
What this question is testing
Whether the candidate knows the general approval requirement that sits over all interceptors and separators, and whether they resist both extremes of banning field-built units and assuming any large box qualifies. It also checks whether they know what a submittal for a job-built device has to demonstrate before a code official can reasonably approve it.
On the job
On restaurant and commissary work the choice between a precast tank and a poured box usually comes down to site access, and either can be made to work. What decides the outcome is the submittal: sizing calculation, section detail showing the baffles and liquid depth, and the access and sampling arrangement. Bring that to the reviewer early, because a job-built interceptor discovered at inspection with no approved design behind it is an expensive conversation.
Memory technique
Right type, right capacity, and the code official says yes.
Exam tip
When a question asks whether an unusual device is allowed, look for a general approval provision before you look for a prohibition.
Where to look it up
Chapter 10, the interceptors and separators section covering approval, type and capacity, and installation per the manufacturer's instructions. UPC differs on this point, so follow the code your state has adopted.