FireEngineeringUniversity.com   •   The Hazards of Modified Fire Apparatus and Extended Passenger Vans

WATER TANK BAFFLES

 

This case study also highlights the issue of water tank baffles. According to the United States Fire Administration’s (USFA) “Safe Operation of Fire Tankers,”5 one of the most crucial aspects of water tank design is the use of properly installed baffles. Baffles are installed inside the water tank to control the amount of water surge that results as the vehicle is moving along the roadway. As explained in the USFA report, if a vehicle rounds a curve, the inertia of the water inside the tank will tend to surge toward the outside of the curve. In other words, as the vehicle is attempting to safely steer through a curve, the water will want to continue in a straight path of travel, pushing the vehicle toward the outside of the curve. This surge of energy could cause the water tanker to lose control or roll over, depending on the situation. Should the water tanker begin to slow down suddenly or attempt a panic stop, the water will continue to move forward, creating a forward surge that will increase the stopping distance of the vehicle and possibly lead to loss of control.

For these reasons, National Fire Protection Association (NFPA) 1901, Standard for Automotive Fire Apparatus, 2003 edition, states, “All water tanks shall be provided with some type of baffles or swash partitions to form a containment or dynamic method of water movement control.”6 The USFA report provides the following explanation of these methods. (5, 68)

  • The Containment Method—This method uses a series of swash plates to divide the tank into a series of smaller, interconnected compartments.
  • The Dynamic Method—This method uses a series of baffles to disrupt the movement of water by changing the direction of travel. These baffles are often staggered so that the changing direction of the water creates a turbulent motion that results in the water absorbing most of its own energy.

However, it is not uncommon for a fire department to place a used or modified vehicle in service as a water tanker without properly examining the inside of the water tank to see if it is properly baffled. Many times, when a vehicle has served as a fuel container in a previous life, it is not equipped with the proper baffles necessary to control the surge of a water load. In the case of the modified 5,000-gallon fuel trailer, the only baffle found inside the tank was a partition that divided the tank into two separate compartments. Although it is not known if the lack of baffles was the primary cause in this crash, this fact is an important learning point for the fire service. Make sure that if you must place in service a vehicle that was previously used to carry a liquid other than water that the tank meets the safety and water baffle requirements set forth by NFPA 1901.