NFPA Expands Aerial Envelope Control Provisions

The first production American aerial control seat with envelope control capability was introduced by RK Aerials of Fremont, Neb. All controls and indicators are within easy reach and sight of the operator.
The first production American aerial control seat with envelope control capability was introduced by RK Aerials of Fremont, Neb. All controls and indicators are within easy reach and sight of the operator.

The trouble with buzzwords is they often get tossed around even though people might not be certain what they mean.

That may be happening with envelope control (EC), the electronic system for controlling aerial devices and keeping them safe. Envelope control has been getting more attention lately, in part because expanded provisions for it were added to the 2009 edition of the National Fire Protection Association 1901 fire apparatus standard.

The new 1901 provisions allow aerials with envelope control – including European-style aerials – to be NFPA-compliant, and they have generated spirited discussion about the wisdom of relying on sophisticated electronics to control aerial ladders and platforms.

Most European aerials are built on lighter, shorter chassis than American ladders to provide greater maneuverability because European firefighters generally operate in tighter quarters with narrower streets. European envelope control systems use electronic sensors to allow aerials to operate safely – including in short-jacked situations – by restricting movement of a ladder when it is in danger of exceeding its limits.

While EC has been drawing increasing attention, it has also generated some misunderstandings. A couple of common ideas about it are not necessarily on target: first, that it is new; and second, that it was developed in Europe.

In some ways it is new, but not entirely. The most basic functions of EC, such as cab and body collision avoidance, have been mandated by the NFPA for about two decades.

Larry Stewart, NFPA fire service specialist and technical liaison to the 1901 committee, noted that since about the mid-1980s, the standard has required both an interlock to prevent the aerial from hitting the vehicle and a means to prevent any operation to the short-jacked side of a vehicle where the stabilizers might not be fully extended. Both capabilities are facets of EC, but they started out as mechanical interlocks, rather than electronic. And forms of mechanical interlocks are still used by some aerial manufacturers in the United States.

Stewart pointed out that technology similar to EC has proved itself in construction cranes and industrial lift equipment for roughly 20 years. In those uses, EC monitors how far a boom or crane can reach and how much of a load it can handle.

The more-advanced electronic EC systems were developed in Europe because of operating conditions that require frequent short-jacking and the need to use aerials as rescue devices in a more vertical position. And European apparatus manufacturers have been at the forefront of bringing more-advanced EC capabilities to the United States.

EC is not a single capability, but rather a suite of related functions, not all of which are accomplished in the same way or are offered by every aerial manufacturer.


Envelope control has advanced steadily from simple capabilities to more complex ones, according to Floyd Bacon, the president of Max Fire Apparatus, a dealer in Castle Rock, Colo.

The most basic electronic function, he said, is cab and body collision avoidance, which is programmable, so the aerial can learn to avoid a rooftop air-conditioner or a warning lightbar.

Auto-bedding, also known as auto-stow or auto-park, is a more-advanced function. Aerials with that capability can “basically put themselves away,” Bacon said.

If an aerial has an interlock to prevent operation to a short-jacked side of the vehicle, that’s a facet of EC. A more sophisticated version, available on some aerials, will let an operator safely use the aerial device on the short-jacked side, though perhaps with less extension and/or tip capacity.

Target Control

Tim McDonald, national aerial sales manager for apparatus builder Rosenbauer America, noted that his company’s EC system senses lift cylinder pressure as a proxy for weight and angle. Another more-advanced function would display any remaining weight capacity in the basket or on the ladder.

Finally, the most-advanced EC capability entering the market, Bacon said, is “target control.” With this function, he explained, “You can teach a ladder points of interest,” such as a window and a point of egress on the ground, while it is operating at an incident. Then, he said, the platform can be commanded to alternate between the two points, along the exact same path each time, potentially speeding up rescue operations.

Each of these functions protects the aerial operator from typical mistakes, according to Bacon, who has seen many aerials damaged by operator error. In all of these functions, he said, the electronic processing is handled “behind the scenes,” in different ways by different manufacturers.

For about the past five years, RK Aerials of Fremont, Neb., has used controller-area network (CAN) bus technology to add EC functions to its aerials, according to CEO Rob Kreikemeier. CAN bus is a subsystem for transferring data between computer components that was designed to let microprocessors and other devices communicate within a vehicle without the need for a host computer. The CAN bus standard, which dates to the 1980s, was designed for automotive applications, but is now also used in other areas.

In addition to the CAN bus, RK’s system of employing EC uses off-the-shelf programmable logic controllers to which RK adds programming that’s specific to the aerial device. Kreikemeier noted that any kind of switch or signal can be fed into the logic boxes, which will let RK add features down the road.

CAN bus has allowed RK to bring all functions into one control station with a single joystick and control panel. RK, a Rosenbauer company, is the only U.S. manufacturer to offer an operator control seat. In addition, it offers a radio remote controller with a small screen to display, for example, a message telling the operator why the ladder isn’t doing what it’s being told to do – that is, how a command would violate the aerial’s safety envelope.

Stewart, the NFPA specialist, pointed out that previous editions of the 1901 standard were written so that an aerial had to have its full rated capacity at full extension in any position. So if you have a 110-foot ladder, he explained, “in the U.S., that has always meant that you can reach 110 feet anywhere,” from horizontal to maximum elevation.

Leery About Use

Ken Creese, sales and marketing manager for aerial builder Sutphen Corp., of Dublin, Ohio, said his company doesn’t oppose EC, but he is leery about how it’s used and how easily operators can adapt to different styles of aerials.

EC and NFPA’s approval of it, Creese said, allow lighter aerials on lighter chassis to be deployed in the U.S. With EC, he said, a 100-foot aerial on a shorter, lighter, more maneuverable chassis may not operate the same as a typical U.S.-style 100-foot ladder in the literal way that firefighters have understood that. He’s concerned about a major shift from the expectations created by previous editions of NFPA 1901.

“We thought it was kind of faking out the end-user a little bit,” he said, because under the 2009 edition of the 1901 standard, a 100-foot aerial with EC may not necessarily reach 100 feet in all scenarios.

In many ways, the situation boils down to a difference of need and history. Fire departments in the U.S. and Europe feel most comfortable with what they’re most accustomed to using.

Aerial device operations in Europe seem to focus more on vertical reach, Kreikemeier said, whereas in the U.S., some fire departments are asking more frequently for aerials that can be used at zero elevation, such as for flood rescue.

Regarding concerns that EC systems could encourage the proliferation of lighter aerials in the U.S., Bill McEnteer, safety officer for the Aspen (Colo.) Volunteer Fire Department and the nearby Basalt & Rural Fire Department, commented that European-style apparatus “sure seem to get the job done” in Europe.

The Aspen VFD operates a 75-foot straight stick aerial with a waterway on a double rear axle chassis with an overall length of about 42 feet, according to McEnteer, who’s also the sales manager for Max Fire Apparatus. The department is looking at buying a 102-foot Metz aerial with EC on a single rear axle chassis that is only 35 feet long and 8 feet wide. It would be no larger than Aspen’s pumpers, and presumably no more difficult to drive.

Safer Aerial Operations

“We keep comparing [Aspen] to a European village” in terms of street size and potential difficulty getting access to a fire scene, McEnteer said.

Adding technology to make aerial operations safer “makes 100 percent sense to me,” he said, especially for volunteer fire departments that don’t typically get a lot of fires.

For departments like Aspen that are in the market for a new aerial, the NFPA’s Larry Stewart has two suggestions:

  • Bring clear specifications to the apparatus builder and focus on what you need the aerial to do, not on the technology.
  • If you decide to use EC, know the aerial’s capabilities and limitations.

In short, he said, “Know what you’re getting when you buy a vehicle.”

Bacon also cautioned that buyers should be clear on the specific capabilities of what they’re looking to purchase because some people use the term “envelope control” loosely.

NFPA 1901 And Envelope Control

New sections about envelope control of an aerial device were added to the 2009 edition of the NFPA 1901 fire apparatus standard. They are highlighted below in bold type:

  • 19.17.5 An interlock system shall be provided to prevent the following:
    1. Rotation of the aerial device before the stabilizer(s) is in a configuration to meet the stability requirements of Section 19.21.
    2. Movement of the stabilizers unless the aerial device is in the travel position.
    3. Operation of the aerial device into an unstable position when the aerial device can be operated with the stabilizers not fully deployed on at least one side of the vehicle.
  • For aerial devices that can be operated over the side with the stabilizers not fully deployed, an indicator shall be located at the operator’s position to allow the operator to determine the maximum extension in relation to the angle of elevation and the extended length of the stabilizers.

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