As a rule, whenever a new edition of a National Fire Protection Association (NFPA) pamphlet is published regarding fire apparatus, there is some controversy. The latest NFPA 1901, Standard For Automotive Fire Apparatus (1996 Edition), is no exception. Since its publication, there has been a great deal of discussion regarding warning lights and low voltage (12-volt or 24-volt) electrical systems.
Photo by Ken Morris Within the fire service, there has been much discussion about warning lights and low voltage (12-volt or 24-volt) electrical systems since the publication of NFPA 1901, Standard For Automotive Fire Apparatus (1996 Edition). This article addresses those issues.
Because there is such widespread confusion on these issues, in this article we will try to address those concerns that have been expressed to manufacturers. This is intended to be a topical discussion of these two major features of the new standard and not a complete technical translation.
Optical Warning Devices
Let's start with the warning light package. In the past, warning lights merited only a few paragraphs in the standard. The new standard, however, features visual warning devices much more prominently and technically. The primary reason for so much attention was the data the committee members had in front of them while making the new revisions.
The most alarming problem the committee saw was that in 65% of reported traffic accidents involving fire apparatus, the apparatus was stationary and was struck from the rear. This would lead one to believe the warning lights were not adequate to overcome the normal curiosity of civilians.
Manufacturers have been fielding a multitude of questions from dealers and customers in regard to the new warning light standards. The most frequently asked question is, "Why do I have to buy all of the warning lights from the same manufacturer?" The answer is, quite simply, you don't have to. The standard does not require that all warning lights be the same brand. What is required is that the apparatus manufacturer must certify that the package installed on an apparatus meets the new criteria. The apparatus builder has three options:
- Certify the visual warning system and its installation based on the lighting manufacturer's published criteria. This is the most expedient way to achieve certification and the one that most apparatus manufacturers are relying on at this point in time. (This has probably led to the common misconception that all lights must be from the same manufacturer.)
- Perform mathematical calculations based on the published measurements for each light and its location. This can be achieved with the information currently available when the upper-level lights are from one manufacturer and the lower-level lights are from another. It can also be done with any array of lights from mixed manufacturers; however, the calculations become much more complex and may lead to additional charges with some apparatus builders.
- Take direct measurements and certify the results. This method is not only complex but it requires a specialized facility and test instruments as well as a great deal of time. Due to this, it is not likely that many builders will offer this as an option in the near future. Light locations are a major part of the new standard as well. The apparatus has been divided into four basic zones: front (Zone A), right side (Zone B), rear (Zone C) and left side (Zone D). In addition, on vehicles 22 feet in length and larger, each zone has been divided into upper and lower areas for a total of eight areas.
Each zone (and each level in each zone on larger apparatus) has specific requirements to meet. Each individual zone has minimum requirements with regards to light intensity in five-degree increments throughout the entire horizontal sweep as well as five degrees above and below the optical centerline. The measurements are the total of all lights in a given zone at each of these measurement points. Special locations or additional lights may be required to ensure a minimum distance of 15 feet between optical centers, or less, for lower-level lights in Zones B and D (right and left sides). As you can see, the exact location of lights has to be engineered rather than chosen for eye appeal.
Further, the standard defines two modes of operation. A minimum requirement has been established for "Calling For Right-Of-Way" while the apparatus is responding to the scene. A separate requirement was established for on-scene duty, or "Blocking Right-Of-Way." The activation of each mode is controlled by the position of the chassis parking brake system (or park position of an automatic transmission on smaller units.) The basic differences lie in the colors allowed and light output in each zone for each mode of operation.
When in "Calling For Right-Of-Way" mode, the light output toward the front is higher than when in "Blocking Right-Of-Way." When in "Blocking Right-Of-Way" mode, light output is increased toward the rear, where accidents frequently occur. Other than the above, there is little difference regarding light output between the two modes.
Allowable colors, within the constraints of local laws, are red, blue, amber and white. In "Calling For Right-Of-Way" mode, red and blue are allowed in all zones, yellow is allowed in any zone except the front (Zone A) and white is allowed in any zone except the rear (Zone C). When switching to "Blocking Right-Of-Way," yellow is allowed in all zones and white is not permitted in any zone. Steady-burning white lights such as scene lights, ground lights and headlights are not restricted.
Ampere requirements have been restricted for the minimum optical warning light package as well. The base maximum draw for the compliant package is 45 amperes for most apparatus. When the length or configuration requires two midship warning lights on each side, the maximum is raised to 50 amperes. When the length or configuration requires three midship warning lights on each side, the maximum is 55 amperes. On apparatus less than 22 feet in length and where the optical center of all warning lights is eight feet or less above grade, the maximum ampere draw allowed for the minimum optical warning system is 35 amperes. Although this sounds like a simple requirement, due to the light output required throughout the entire circumference of the apparatus, this single aspect of the new standard has led to major headaches for lighting manufacturers.
Besides the above-listed major considerations, there are requirements for minimum flash rates, detailed procedures to measure light output and more. These items mostly apply to lighting and apparatus manufacturers. While those items are important, we will not address them in this article since they have not invoked nearly as many questions as the above-listed aspects of the new standard.
As a result of the new requirements for a minimum light package, your basic system will be optically and electrically more efficient than systems in the past. It must be understood that more lights may be installed in addition to the minimum package to resemble current installations but these lights will need to be directed through the electrical system load manager.
Low Voltage Systems
This section saw a major revision. It was compelled by problems that have plagued the fire service for years and years. Upon looking to the future, it was realized that the situation had to be controlled due to the advent of computers on just about all aspects of the apparatus. Computers need steady, predictable current; when the available voltage drops too low, they shut down. The results can be catastrophic if the apparatus is engaged in heavy fire combat and the computer on the engine cannot get enough voltage.
The major feature of this section is a new requirement that the alternator be sized to provide enough or more than enough amperage to meet the minimum continuous electrical load, at idle, at 200 degrees Fahrenheit. The ratings we are all used to seeing on alternators are normally obtained at room temperature. Actual output in a hot engine compartment is, as a rule, dramatically less. Another mitigating factor is that output at idle can be higher for some 270 ampere alternators than other 350 ampere alternators. This means the alternator, its respective output curve at 200 degrees F and even alternator pulley ratios must receive extremely close scrutiny.
The minimum continuous electrical load (i.e., the absolute minimum requirements for apparatus operation) is defined in the standard as:
- The engine and transmission.
- Lights required by the Federal Motor Vehicle Safety Standard (FMVSS), which include headlights and marker lights.
- Two-way radio at a minimum of 5 amperes.
- Ground, walkway and control panel lighting as well as half of all compartment lights.
- The minimum optical warning system in "Blocking Right-of-Way" mode.
- Power required by the pump, aerial, and hydraulic pumps.
- Anything else the purchaser decides is critical to the mission of the apparatus.
As you can readily see, that is quite a load. Knowing that the minimum load is fairly large to begin with, the committee then requires a load management system when the total connected electrical load (i.e., minimum continuous electrical load plus all additional loads) exceeds the rating of the alternator under the idle and temperature conditions previously noted. This means that nearly all apparatus will be required to have a load management system. It must be noted that none of the items under the definition of the minimum continuous electrical load may be shed by the load management system.
To alert the operator in the case of imminent failure of the apparatus, the pamphlet calls for a system to monitor the condition of the low voltage electrical system by direct measurement of the batteries or by monitoring the system voltage. If the system voltage is monitored, this system must be set to trigger when the system voltage drops below 11.8 volts for more than two minutes. The 11.8-volt setting should be far enough above the failure point of most electronics to give the operator time to be prepared if complete failure should occur.
Once the apparatus builder has completed the unit, it must be tested and certified. Certification that the required tests have been performed and the unit passes must be provided with the apparatus at delivery. The tests include a reserve-capacity test, an alternator performance test at idle, an alternator-performance test at full load and a low-voltage-alarm test. The pamphlet spells out the exact sequence and procedure for each test. If the apparatus fails any one test, the entire sequence must be performed from the beginning.
We hope this article has helped you more clearly understand the new standard. We highly recommend getting your department a copy of the standard and reading it thoroughly for a more complete understanding of its content. (To order a copy, call NFPA customer support at 800-344-3555.)
J.R. Ford works in the sales department at Smeal Fire Apparatus. He has been in the fire service industry for 20 years, starting as an apparatus mechanic and working his way up to sales through dealer organizations. Sheri Quinn has been with Code 3 Inc. for 11 years, including two years as OEM sales manager. She has a bachelor of science degree in business management from Maryville University in St. Louis.
