Issue 02 / April 2010
The Differences In UL142 Fuel Tank Construction
By Pete Torres, Pro Power Solutions
During a preliminary design meeting for an indoor diesel set, a consulting engineer asked, “When we specify the diesel generator’s tank to be supplied as a “UL 142 Base Tank”, what tank construction will be submitted?
Given today’s competitive market, open bid projects are quoted with a minimum bill of materials that meet the project’s plans and specifications, all in order to be the low bidder to win the project. If a specification only references that the tank be classified as UL142, design options can be submitted that are low in cost, but may not meet code approval for both indoor and outdoor applications.
There are five basic types of Generator-Base Tank designs that can be Underwriters Laboratory (UL) Listed as “Special Purpose Flammable Liquid Tanks”. The basic “standard” for these tank designs is an Underwriters “UL-142 Steel Aboveground Tanks for Flammable and Combustible Liquids” listing. Tank designs are known by various industry slang names, and in some cases the same name is applied to several different types of tank. This has been very confusing and misleading. The five different tank designs are in the following UL categories:
- single wall tank
- open-top diked tank
- closed-top diked tank
- secondary-containment generator tank
- protected secondary tank (UL 2085)
Any of the following options may be submitted by a “low bidder” if the tank’s requirement is only UL142:
Open-Top Diked
This is a “double wall” tank, and the side rails of the dike (or rupture basin) have been designed to support the weight of the generator set. The inner tank is attached to the dike and the dike is open to the atmosphere. This type tank offers little protection against falling debris or precipitation from entering the containment basin.
This tank has been traditionally installed indoors and out of the weather; however, current venting code issues for indoor applications, if enforced, would likely prohibit the local jurisdiction having authority (LJHA) from awarding approval.
Closed-Top Diked
This is a “double wall” tank, and the side rails of the dike have been designed to support the weight of the generator set. The inner tank is attached to the dike and the dike is covered with one end open to the atmosphere. The cover for the dike is vented at one end to keep rain and debris from entering the dike. When this tank is UL Listed, it will include an emergency vent connection on the inner tank only.
This application is typically acceptable by LJHA’s for outdoor use; however, there is no true connection to pipe the normal vent to the exterior of a building for an indoor application. Also if the local codes require the vents to be extended above the generator enclosure, there is no way to extend the normal vent.
Secondary Containment
The Secondary Containment (Double Wall) Generator Base Tank is a true double wall constructed tank, the rails of the outer tank have been designed to support the weight of the generator set. This is the only form of generator base tank recognized by Underwriters Laboratories as a “double wall”. Both the inner tank and outer tank must be pressure tested to 3 psi. When this tank is UL Listed, it will include an emergency vent connection on the inner and outer tank.
If the application is an indoor generator and skid tank, then a Secondary Containment tank should be specified so both the normal and emergency vents can be piped and extended to the exterior of the room.
All tanks manufactured by Generac Industrial Power are UL 142 Secondary Containment tanks suitable for use both indoors and outdoors!
