Hybrid School Buses: Response Considerations

BY LEIGH T. HOLLINS

In February 2007, the Manatee County (FL) School District took delivery of the nation’s first diesel-electric hybrid school buses, according to news reports. The school buses were built by Enova Systems and IC Corporation as partners in the growing market of hybrid commercial vehicles and trucks.

There are two main types of hybrid vehicles: the hybrid electric vehicle (HEV) and the plug-in hybrid electric vehicle (PHEV). HEV vehicles recharge their battery bank as the vehicle is driven and are known as “charge-sustaining” vehicles. PHEV veh0801FE107-110.htmlicles must be plugged into an electrical outlet to recharge the battery bank and are known as “charge-depleting” vehicles.

(1) This is the first hybrid school bus in service in the nation. These new hybrids have 1,680 pounds of lithium ion batteries and protective frame on one side, offset by 1,680 pounds of steel counterweight on the opposite side. Will this affect your operations? Yes, such factors as dealing with high voltage and stabilizing a bus that has rolled onto its roof with an extra 3,400 pounds as the new high center of gravity will alter your tactics. Where is the high-voltage cable? Left side middle, under the bus. What color is the cable? Orange one-inch cable. Where is the emergency high-voltage shutoff switch? Left side, under the bus, at the front of the battery bank. (Photos by author; drawings used with permission of Enova Systems.)

What makes hybrid commercial vehicles attractive to the consumer is the 30 to 55 percent fuel economy improvement and up to 90 percent emissions reduction. Additionally, the manufacturer claims reduced maintenance, improved performance, and a quieter vehicle.

The components of the new diesel-electric hybrid school bus include the following:

• an 80-kw electric motor;
• a battery care unit (BCU), which monitors battery condition;
• a safety disconnect unit, which is controlled by the BCU;
• a battery bank, which contains 28 12-volt lithium-ion batteries in series;
• a separate cooling system, with an isolated radiator; and
• a control electronics unit (CEU), which contains the electronics.

EMERGENCY RESPONSE CONSIDERATIONS

How do hybrid school buses affect the emergency response when involved in a crash or a fire? From a response standpoint, a few issues to consider that are unique to a hybrid school bus include weight distribution, high-voltage electrical systems, and a bank of 28 batteries. Under normal circumstances, none of these issues will present a problem to emergency responders. However, during certain situations, the hybrid components may present a hazard to emergency responders, and we must prepare for these situations.

Weight Distribution

This factor should require little thought or preparation. All that’s needed is awareness of what you are facing and a little common sense. The battery bank, located on the left side, just front of the center, under the bus, is made up of 28 12-volt batteries. The batteries are protected by a framework of heavy steel, which is the same as or similar to the frame that protects the fuel tank on a school bus. Together, the weight is 1,680 pounds. On the right side, same position, is a similar steel frame that contains steel counterweights that weigh—you guessed it—1,680 pounds. So, the grand total weight of the batteries, the steel frames, and the counterweights is 3,360 pounds.

Now, add the 600-pound electric motor and the 140-pound control electronics unit (CEU). The grand total is now 4,100 pounds—more than two tons of weight. This weight provides a very low center of gravity for a bus on its wheels. However, if the bus is on its side on unsteady terrain (other than a hard, flat surface) or rolled onto its roof, you now have a very high center of gravity to deal with. Several long struts and straps or a couple of wrecker trucks (make sure they are large enough) will be needed to safely stabilize the bus.

Batteries

The hazard presented by 28 12-volt batteries involved in a crash or fire situation may be significant. The type of battery is lithium ion, the same as the battery on most cell phones. There will be greater than normal amounts of battery electrolyte. The electrolyte, however, is not in a liquid state; it is absorbed in the battery cell plates. In this state, there should not be a “spill” should the batteries be breached during a crash, although the breach may cause electrolyte vapors to be present. To deal with such vapors, avoid breathing them and move any victims away from them as soon as possible. Use SCBA, when appropriate. If electrolyte comes in contact with gear, tools, skin, or eyes, flush with large amounts of water.

(2) Note the location of the battery bank under the bus, between the “606” and the word “MANATEE.”

Should the batteries become involved in fire, treat them as live high-voltage electrical equipment, which would dictate the use of any Class C extinguishing agent. Use full respiratory protection (SCBA) because of the toxic nature of the products of combustion resulting from a burning lithium ion battery.

High-Voltage System

A little knowledge and some common sense apply here also. The 28 12-volt batteries are wired in series, producing 336 volts—about three times the voltage of normal household current. So, use extreme caution when operating around such high-voltage systems.

(3) Avoid all orange high-voltage (HV) cables. These cables are confined to a rather small area under the bus, generally between “LIMPIO” and “606” in photo 2.

The general rule is avoid any orange-colored cables or wires. If you follow that one rule, the high voltage will be a nonissue. However, like most things, there are situations when that may not be enough precaution, such as when an orange wire is crushed or penetrated by the force of a crash. So, how do we deal with the situation? The answer is rather simple as long as we can access three places on the bus: the ignition key, the dash area left of the steering wheel, and the area on the front of the battery bank. Do the following:

1. Turn off the ignition key and remove it.
2. Turn off the hybrid system switch on the dashboard.
3. Turn off the service disconnect (read as emergency high-voltage shutoff switch) on the front side of the battery bank.

(4) The hybrid system dashboard panel indicates the status of the system, as well as provides an on/off switch for the driver’s use of the HV electric motor and its components.

After I discussed this conflicting information with the Enova engineers, they advised me that the last statement was included because during an event causing extensive damage, it cannot be guaranteed that the service disconnect switch would dissipate all high voltage in the system. When asked, “If I turn the service disconnect switch off, will it kill all power beyond the switch?” the engineers’ answer was, “It should.” My advice is that it is a main disconnect switch from the battery bank to all other components, and I would treat it as an emergency high-voltage shutoff switch.

(5) The location of the service disconnect switch is on the front side of the battery bank.

The bottom line is, be aware of the weight distribution issue, know how to identify a hybrid school bus, fight electrical fires with Class C agents, keep away from electrolyte and its vapors, follow the procedures for securing the high-voltage system, and avoid any orange cables or wires.

(6) Here, the front side of the battery bank is shown, as is the steel protective frame. The “service” switch and orange HV wire are plainly visible. Note: The Enova Hybrid School Bus – Emergency Response Guide describes the above procedures but also states: “Under no circumstances should this switch be treated as an emergency cutoff switch.”

For additional information and to access the operator and emergency response guide, go to www.enovasystems.com. Click the support button and scroll down to the documents.

(7) This picture shows several items: two hybrid identifiers—one above the door and one just right of “LIMPIO” (LIMPIO is the name of the bus, which means clean in Spanish). The 1,680 pounds of counterweight are shown under the bus; the yellow square is the outlet for plugging the bus into an electrical source when not in use.

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LEIGH T. HOLLINS began his career in 1976 at Nottingham Fire Company in Hamilton Square, New Jersey, before relocating to Manatee County, Florida, in 1977. He is a battalion chief in the training division at Cedar Hammock Fire Rescue and vice president and director of Starfire Training Systems, Inc. Hollins produced Fire Engineering’s School Bus Extrication DVD and instructs frequently throughout the United States. He is a lead instructor for FDIC’s Hands-On Training program and is a member of the FDIC educational advisory board and of the Fire Engineering editorial advisory board.