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How to choose the correct cover for your interceptor

How to choose the correct cover for your interceptor

February 1, 2023

How to choose the correct cover for your interceptor post image

Choosing the right cover(s) for your new or existing grease interceptor may be confusing - especially when the options and terminology differ by manufacturer. And it’s a more important decision than you might think, as things like safety and odor must be taken into consideration.

Schier has recently made changes to its cover options to include a new pedestrian-rated composite cover - a move we’ve made to help clear up confusion surrounding when and where to use which cover. As such, this blog focuses on “cover type” education and choosing the right one for your specific application. Let’s dive in.

Schier Covers

H-20 Rated Cast Iron

This heavy-duty cover is typically used in outdoor, buried installations where vehicle traffic may occur. It has an H-20 rating, which is a load bearing requirement determined by The American Association of State Highways and Transportation Officials (AASHTO). H-20 requires that a cover meet the designated load of 16,000 pounds per wheel without a safety factor. Furthermore, AASHTO M306 specifically applies to cast iron covers and requires a 2.5 safety factor. This amounts to a proof load rating of 40,000 pounds (2.5 x 16,000).
Schier traffic rated cast iron coverProduct details:

  • Cast iron

  • Pickable 24"

  • H-20 rated

  • Rated to 16,000 lbs per AASHTO M306

  • Gas/water tight

  • Typical for outdoor installations or indoor installations with vehicular traffic

  • Cover material: cast gray iron ASTM A-48, Class 35B

Pedestrian Rated Composite

This new addition to the Schier cover lineup is typically used for indoor installations and should be used in areas where vehicle traffic would not be present. For example, an “indoor” parking garage would not be a suitable location for this type of cover. This bolted cover is used primarily where a completely airtight seal is needed and a lighter, more easily serviced cover can be used. It is also recommended for any above grade installation where the lifting of a heavy cover poses a risk to both the person performing the service and the surrounding finished floor.

Schier pedestrian rated composite coverProduct details:

  • Composite

  • Bolted 24"

  • Rated to 2,000 lbs per CSA B481.0, Class M

  • Gas/water tight

  • Typical for indoor installations and above-grade installations

  • Cover material: glass reinforced polymer

GB-50 installed indoors in restaurant basementExceptions and Special Circumstances

There are applications where a gray area may exist between indoor and outdoor installation. 

Composite cover outdoors (not typical)

One instance in which you should choose a composite cover for outdoor installation is when your interceptor is installed above grade (not buried). This is because heavy-duty cast iron covers are more difficult to remove and replace when the tank is above grade, and their weight can deform the neck gasket without additional support. 

GB-500 installed above grade in garage

A second situation in which you may choose a bolted composite cover outdoors is if an interceptor is installed in a green space and not at risk of more than a 2,000-pound load. This would be especially true if an outdoor dining patio were situated nearby. The cast iron cover that would typically go outdoors may release some level of odor through the seal, so in these circumstances you may consider a composite cover outdoors for a better dining experience.

Cast iron indoors (not typical)

As mentioned earlier, there are situations where an application may technically be indoors, but vehicle traffic would be present. Some examples would be a parking garage, a location where forklift activity is present, a garage of a restaurant where a food truck is parked/stored, etc. In these cases, a pedestrian-rated cover would not be appropriate or safe.

In a Nutshell

To summarize, the best rule of thumb is to use composite covers for indoor installations and cast iron for outdoor, buried installations. There are some exceptions, but the Schier website has safeguards in place to guide you in choosing the right cover for your situation, whether unique or typical. Through the selection and checkout process, you will be prompted to answer two questions about your installation, which may result in a modal prompting you to reconsider your selection. See below.


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