The Standards That Govern Grease Interceptors (All Types) in North America

March 11, 2014

UPDATED (June 2014)

When it comes to grease interceptors there are a variety of recognized standards that have been developed over the years that govern performance requirements, construction requirements or both. This post will explore all of the available standards for North America and the types of interceptors they govern.



PDI-G101
This standard governs passive hydromechanical grease interceptors.

PDI stands for the Plumbing and Drainage Institute which is an association of manufacturers of plumbing and drainage products. In the early 1940's PDI was called the Plumbing and Drainage Manufacturers Association and members of the group joined with representatives of the Quartermaster General, Surgeon General, Army Corp of Engineers and researchers from the Iowa Institute of Hydraulic Research to develop a testing program to establish flow rates and grease holding capacities for uniform rating of grease interceptors.

Using the guidelines established in Iowa, the Research Committee continued the testing program at The United States Testing Company, Inc., which culminated with the first issue of this Standard in 1949 and certification of applicable grease interceptors.

Test apparatus used by PDI and ASME



Interceptors are tested and rated for efficiency and grease storage capacity. Approved interceptors will have a minimum average grease removal efficiency of 90% and will retain not less than 2-1/4 lbs of grease for each one gpm of certified flow rate at either the interceptors Rated Grease Capacity per Table 1 below (with a 12.5% safety factor) or at the interceptors Maximum Grease Capacity by determining the break down point.

Certification to a Rated Grease Capacity allows a manufacturer to test their unit through 13 cycles and whether "full" of grease or not, so long as the interceptor meets the requirements for efficiency and the minimum grease capacity per Table 1, it will be certified at the Rated Grease Capacity per Table 1.

The standard also allows a manufacturer to have an interceptor tested to break down to determine its Maximum Grease Capacity. It must meet the same efficiency requirements and minimum grease capacity as an interceptor with a Rated Grease Capacity and so long as it does, it will be certified.

Interceptors that are certified to a Rated Grease Capacity and those certified to a Maximum Grease Capacity are required to label their interceptors the same according to Table 1 above. This essentially discourages manufacturers from continuing to test an interceptor beyond 13 cycles to determine the interceptors break down point because the interceptor will still be certified and listed to the same performance as a Rated interceptor. This makes it difficult to determine if an interceptor certified to PDI-G101 actually exceeds the minimum requirements.

This standard also mandates the use of an external flow control with integral air vent (which provides air entrainment to aid grease in separating from the entering waste stream) and internal baffles or barriers. Currently the standard does not allow for any alternative design elements, which discourages innovation.

Lastly, the standard provides language that would imply that a manufacturer could have an interceptor tested and rated to flow rates in excess of 100 gpm. Unfortunately PDI does not have the ability to actually perform the testing at this time. Currently the maximum flow rate of any interceptor certified to this standard is 100 gpm.

This is the most widely used, recognized and approved standard in North America.

According to PDI's website there are 24 manufacturer's with grease interceptors certified to this standard.

PDI G-102
This standard sets requirements for how grease interceptor sensing and alarm devices perform to signal that the interceptor is approaching its rated capacity.

PDI launched this standard in 2009 and to my knowledge the only manufacturer's of sensing and alarm devices that have certified to this standard are Canplas and Josam.

ASME A112.14.3
This standard governs passive hydromechanical grease interceptors.

According to the foreword, “In 1994, the Plumbing and Drainage Institute agreed to work with the American Society of Mechanical Engineers for the development of this Standard. This Standard includes criteria for testing and rating of grease interceptors; general requirements for these appurtenances; and an appendix of valuable sizing, installation, and maintenance data.”

Regarding the scope of the Standard the foreword states, “…this Standard is limited to units of 100 gallons per minute (gpm) or less in rated capacity.”

One of the significant differences between PDI G-101 and this Standard is that while PDI G-101 interceptors are restricted to design requirements that include a vented external flow control and internal baffles, this standard classifies interceptors with these design elements as Type “A” Rated.

Type A – Units with external flow control, with air intake (vent), directly connected
Type B – Units with external flow control, without air intake (vent), directly connected
Type C – units without an external flow control, directly connected
Type D – units without an external flow control, indirectly connected

I am not aware of any manufacturer who has certified an interceptor to Type B at this time.

Schier Products Great Basin series and Thermaco's Trapzilla series are the only grease interceptors currently certified to Type C. Canplas' new Endura XL series, which they are advertizing as available this fall, also utilize built-in flow control conforming to Type C.

I am not aware of any manufacturer who has certified an interceptor to Type D at this time.

While the testing under ASME A112.14.3 is identical to that under PDI G-101, there are a couple of differences in performance and rating requirements.

PDI G-101 requires an interceptor to hold 2-1/4 lbs of grease for each one gpm, while the ASME standard only requires 2 lbs for each one gpm.

PDI G-101 allows for either Rated Grease Capacity or Maximum Grease Capacity, while ASME only allows for Maximum Grease Capacity.

ASME A112.14.3 is listed and approved by the Uniform Plumbing Code (UPC), the International Plumbing Code (IPC) as well as the National Standard Plumbing Code (NSPC) and most independent state plumbing codes.

ASME A112.14.4
This standard was first published in 2001 and is the only recognized standard in North America governing automatic grease removal devices (GRD).

The devices required to meet this standard must automatically remove fats, oils and grease from the separation chamber to a point outside of the GRD in a container capable of holding 150% of the interceptors rated capacity. The removal process is supposed to ensure that the removed FOG is 95% free of water, by volume.

The standard mandates that GRDs first be tested and rated according to ASME A112.14.3 to establish that the interceptor's separation chamber can hold 2 lbs of grease for each one gpm of flow rate. Then the standard employs an additional test to ensure that the GRD's collected grease can meet the required percent of water content, not to exceed 5%.

ASME A112.14.6
This standard was developed to address a growing category of interceptors that not only separate and retain FOG, but internally dispose of retained FOG by means of mass and volume reduction through thermal, chemical, electrical and biological processes.

The standard allows for the use of hydromechanical grease interceptors meeting either PDI G-101/ASME A112.14.3 or gravity grease interceptors meeting IAPMO/ANSI Z1001.

Acceptable performance, under the test parameters of this standard, is an effluent concentration limit of 100 mg/L (PPM) as determined using USEPA Method 1664.

CSA B481
This is a consensus standard published by the Canadian Standards Association in 2007 governing hydromechanical grease interceptors. It is a more comprehensive standard that governs material requirements, construction requirements, test methods and performance requirements, marking requirements and sizing guidelines.

CSA both publishes Standards and offers testing and certification services to those standards for a fee. They also allow other certified/approved agencies to test and certify to their standards. Testing agencies have their own identifying mark as follows:

This mark identifies an interceptor that has been tested and rated by CSA Group to CSA B481.


This mark identifies an interceptor that has been tested and rated by IAPMO to CSA B481.


This standard offers two different types of ratings; B481.1 and B481.2.

CSA B481.1 Testing and rating of grease interceptors using lard
This certification specifically requires testing to ASME A112.14.3 for the interceptors flow rate and rated capacity and requires the interceptor to be marked with its removal efficiency, flow rating, and maximum grease containment capacity.

CSA B481.2 Testing and rating of grease interceptors using oil
This certification uses effluent concentration sampling for testing the interceptor. The test requires the interceptor to be filled with water first, then have crushed granite added up to the interceptors maximum solids capacity (unless the interceptor is not designed to capture and contain solids), then fill the interceptor with sunflower oil to the point at which 5 test cycles of 12,000 mg/L will fill the interceptor to its rated capacity.

Then the interceptor is tested 5 cycles with the oil mixture in the prescribed concentration and the interceptor’s effluent is sampled multiple times during the cycle. Whatever the average is of the concentration of oil in the effluent grab samples is recorded as the average efficiency for the interceptor in mg/L.

For demonstration purposes let’s say an interceptor’s first cycle has an average effluent concentration of 100 mg/L, 2nd cycle its 120 mg/L, 3rd cycle its 130 mg/L, 4th cycle its 175 mg/L, and 5th cycle its 225 mg/L. The interceptors overall average efficiency would be 100 + 120 + 130 + 175 + 225 = 750 divided by 5 for an average of 150 mg/L. The manufacturer would then be required to post the interceptors Effluent Grease Concentration as 150 mg/L on its label.

There is no predetermined concentration limit that triggers a pass or fail. The test simply requires the manufacturer to list the grease concentration limit as an average of the recorded test results.

There are no certified grease interceptors that meet this standard today.

ASTM C 1613
This is a standard specification for Precast Concrete Grease Interceptor Tanks. It governs the type of cement, method of manufacturing as well as structural and physical design and construction requirements including: the shape and capacity of the tank, number of compartments, location of baffles, minimum and maximum liquid height, volume of free airspace, size and location of manhole covers, and so on.

The only testing requirement contained in the standard is for water-tightness. There is no performance test requirement.

This is not an approved standard in either the Uniform Plumbing Code nor the International Plumbing code.

IAPMO/ANSI Z1001
This is the primary standard governing gravity grease interceptors (GGI), recognized by national model plumbing codes and most independent state plumbing codes. It governs design requirements such as a minimum of two compartments, minimum liquid volume of 300 gallons, minimum free airspace, size and location of manholes covers, and so on. It also governs construction material requirements including concrete, fiberglass, polyethylene and coated steel.

The major drawback to the standard is that it does not require a performance test for certified units, but rather only mandates leakage testing.

Future work on this standard should focus on developing a test protocol to justify detention time based sizing methodologies.

Now you know all of the standards that govern grease interceptors today, the types of interceptors or technologies that are covered and the basic requirements contained in each standard.


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