One of the most common causes of fires associated with earthquakes is the rupture of gas lines when the water heater overturns. Water heaters are usually very tall, heavy (because the are filled with water) and narrow. These characteristics make them vulnerable to tipping over during an earthquake and starting a fire by breaking the attached gas or electrical lines (Figure 1).
Water heaters are usually set on the floor or on a pedestal. Until recently, codes did not require water heaters to be braced. The earthquake shaking produces lateral forces on the water heater at its center of gravity. The higher the center of gravity, the less force will be necessary for the water heater to overturn.
Question: How can you prevent a water heater from overturning?
Answer: To prevent the water heater from overturning:
1. Water heater must be braced at the top and the base.
2. Rigid connectors for the heater gas and water piping must be replaced with flexible connectors.
Because earthquake forces can make a water heater shake in all directions, a water heater must be braced at both the top and bottom. New water heaters are installed on platforms.
The top brace is used to prevent the water heater from tipping over. The bottom brace is necessary so that the base of the water heater will not move far enough to shift and slide out when the earth is shaking. The State of California has approved several typical details (Figure 2). There are other prepackaged systems that have been approved (Figure 3).
In the typical details for the smaller water heaters, plumbers tape is commonly wrapped around the top and base area of the water heater. Struts are attached to the plumbers tape and then anchored into the wall framing using lag screws. EMT conduit works well as a strut. The ends can be flattened and drilled to attach the lag screw or bolt. Sample details are included below.
For strapping of the water heaters it is critical that:
- Plumbers tape or strap is wrapped all the way around the water heater.
- Lag screws are anchored into a stud. The stud must be one that is continuous from the sill plate to the top plate.
- Struts are used to brace the water heater to straight sections of walls. Plumbers tape only works in tension and has no strength to resist compression.
- Lastly, gas and water connectors must be replaced with flexible connectors and the flue should be braced. Flexible connectors allow the water heater to move several inches without breaking.
During an earthquake a braced water heater will still make some movements because of the slack and stretching of the straps. Even if the water heater moves only a small distance, the connectors may break if the connections into the water heater are rigid. The break can cause the water to flood the area or more seriously, cause a gas leak.