Low-Emission Transfer and Redundant Fail-Safe Product Control Measures

(August 30, 2017) Low-emission transfer is gaining popularity with the increasing use of propane, often referred to as autogas, in over-the-road vehicles. Redundant fail-safe product control measures (RFPC) is an associated concept to enhance safety. They permit separation distances to be reduced to enable installations that otherwise could not be allowed. However, our inspectors are finding places that are claiming the benefits of low-emission transfer without properly considering the rules.

I apologize up front for the complexity of this article and for the references that clutter it. This is not a well-understood idea by many people who are considering its use. I will attempt to point out at least some of the nuances, but technical descriptions are necessary to convey the concept.

Low-emission transfer is defined in the LP-Gas Code as “a method to transfer LP-Gas liquid that limits the amount of propane released during the transfer.” (NFPA 58 section 3.3.44, 2017 edition) The allowed limit released when breaking a connection and still qualify as low-emission transfer is:

  • 0.24 in.3 (4.0 cm3) (about 4/5 of a level teaspoon) per uncoupling for deliveries to stationary ASME containers when using a hose of 1-in. nominal size or smaller or to permanently mounted ASME engine fuel containers on vehicles. ( and
  • 0.91 in.3 (15 cm3) (about one level tablespoon) when delivering to a stationary ASME container using a hose larger than 1-in. nominal size. (
Release of product through the fixed liquid level gauge (bleed valve, outage gauge, etc.) while filling or afterwards is not permitted.

To meet these requirements, the equipment used in these transfers must specify the amount of product released when it is uncoupled. I will talk more about that later.

You may have noticed that a common requirement, “ASME containers,” is present in each of the referenced sections. The whole of section 6.30, when it was added to the 1998 edition, was intended to apply to autogas filling. The RFPC measures allow a large container installation, up to 30,000 gal.—underground or mounded only—on a small “gas station” lot. Specified tank appurtenances and control features in 6.30.3 and 6.30.4 enhance safety by being a couple of degrees more rigorous than normal requirements. Low-emission transfer requirements further enhance safety by releasing only small amounts of flammable product after a fuel delivery to either a vehicle’s tank or to the storage tank at the facility. The LP-Gas Code Handbook has excellent, detailed explanations of the many features involved. Note that RFPC measures and low-emission transfer are not limited to autogas use only. The application statement in 6.30.1 permits use of these features in other situations.

The reward for installing these premium tanks and fittings and for releasing only very small fugitive emissions is a reduction in separation distances. However, there is never mention in the code of filling cylinders using low-emission transfer. Also, hot-air balloon containers may not be filled at a low-emission transfer location.

With that in mind, let’s deal with the cylinder question first. You may not claim a reduction in separation distances when filling cylinders. The code does not prohibit filling cylinders per low-emission transfer rules. But, neither does it provide for claiming the advantages of reduced separation as is allowed for filling ASME containers. Every place where the code allows reducing the separation says that it is doing so per rules for ASME tanks. I understand that California has rules that limit fugitive emissions, so filling cylinders with low-emission-rated nozzles is normal in that state and may be required.

I can see where this reduced separation could be beneficial for cylinder filling, so I may approach the 58 committee with the idea of making code changes for doing so. It will take more research to be sure there is a sound basis for doing this. Even then, there is no guarantee on how the committee will respond.

Hot-air balloon containers, those labeled as being FAA approved, may not be filled per low-emission transfer rules. (These containers are neither DOT cylinders nor ASME tanks; they fall in between, but meet neither specification.) They are normally filled while in place in the basket by bleeding each container. This method is not permitted under low-emission transfer rules. But, that really doesn’t make any difference, as FAA-approved containers may not be filled by low-emission transfer rules.

With regard to how this affects transfers to ASME tanks, most gasoline stations don’t have enough property to install a large (more than 2000 gal.) propane tank, even underground, using the normal separation rules. They also don’t always have enough room for the required separation from point of transfer to buildings, other dispensers, or property lines. If a station is designed with all the requirements of RFPC measures and low-emission transfer, then a 30,000-gal. UG or mounded tank may be installed as close as 10 feet from a building or property line and certain separation distances specified in Table may be halved. (The code contains an apparent internal inconsistency about applying this to all distances in Table The committee is working on this.)

If the intent is to fill engine fuel containers for over-the-road vehicles, then a Propane LP-Gas dispenser, as defined in, is expected to be used. (6.27.5) (This is vague and may not be a requirement.) These dispensers must be equipped with low-emission transfer systems. They look a lot like gasoline dispensers, I expect in an effort to add familiarity as customers make the switch to autogas and to make installation of all dispensers somewhat uniform.

I recently spent a lot of time at the International Propane Expo in Nashville looking at and discussing low-emission-transfer equipment. There are some filling nozzles with impressively low-release volumes, but that is only half of the story. You also must consider the volume that will be released by the other half of the connection—the fill valve. Very few of the fill valves shown in the catalogs I picked up indicate a release amount. Be sure to select components or a combined unit that does if you want to claim the credit. My interpretation is that a fill valve without a specified release amount does not qualify for low-emission transfer.

Use of adapters between the filling nozzle and the fill valve adds to the amount of released product. The internal volume of the adapter must be added to the amounts released by the nozzle and the fill valve to determine the total amount released. Use of any such adapter will almost certainly exceed the limits of low-emission transfer. This combination of equipment — low-emission nozzle and fill valve but with an adapter for cylinder filling — seems to be the basis for some speculative requests for dispensers to be low-emission transfer sites. Be sure to verify the released amount, by equipment rating, before committing to a site.

I recently visited a site that was installed with the idea of low-emission transfer. It was intended for filling cylinders only. It did not meet the separation requirements of Table and, as explained above, could not reduce those separations. We could not identify a place on the site that met all the requirements. I encourage you to ask questions of your enforcement personnel or equipment supplier before you invest in a site you can’t use.

You also need to be aware of a couple of other requirements:

  • Containers may not be filled using the fixed maximum liquid level gauge (bleed valve) at a low-emission transfer site. Weighing is not an option for containers permanently mounted to a vehicle or for bulk tanks. The only option is to depend on the stop-fill device or overfill-prevention device, which must be verified for its proper operation at least annually. ( and
  • Those who fill these containers must be trained. (11.2)
  • The site shall be identified with a sign as “Low Emission Transfer Site.” (
  • What about those RFPC measures requirements? Section 6.30.3 specifies the container appurtenance requirements:
  • All container withdrawal openings that are 1¼ in. or larger shall be equipped with an internal valve. Note, this does not allow for the alternative of excess-flow valve, ESV, and control valve.
  • The internal valves shall remain closed except when fuel is being transferred.
  • The internal valves shall be equipped for remote closure and automatic, thermal shutoff.
  • A positive manual shutoff valve shall be installed as close as practical to each internal valve.
  • All container inlet openings shall be equipped as above or with a backflow check valve and a positive manual shutoff valve.
  • Section 6.30.4 specifies some strong product control measures:
  • All requirements in 6.14 for use of emergency shutoff valves and/or backflow check valves apply when filling the dispenser supply tank from a cargo tank vehicle or railroad tank car.
  • The whole system (internal valves and ESVs) shall shut down automatically through thermal actuation and in the event of a hose pull-away.
  • Remote shutdown of these valves and the power supply for the transfer equipment shall be provided by properly labeled remote shutdown stations both within 15 feet of, and 25 feet to 100 feet from, the point of transfer.
All of this may seem to be a lot of expense and trouble. It is, but this high level of redundant, specially designed equipment and attention to details when transferring product allows the installation of a dispensing site on a significantly smaller piece of property than would normally be allowed.

By Richard Fredenburg, the LP-gas engineer at the North Carolina Department of Agriculture and Consumer Services.

(Pubished in the August 2017 issue of BPN magazine)