When a thunderstorm rolls in, seeking shelter indoors does not eliminate all risk of being struck by lightning. While most lightning casualties occur outdoors, about one-third of lightning-related injuries happen inside a structure. This occurs because the immense electrical charge from a lightning strike can follow conductive pathways that extend inside the home. Understanding these routes is necessary for ensuring safety during severe weather events.
How Lightning Enters the Home
The primary danger of showering during a thunderstorm stems from conductive materials connecting the interior of your home to the outside world. Lightning seeks the path of least resistance to the ground, often traveling through a building’s utility systems, such as electrical wiring and plumbing. Residential plumbing, particularly in older homes, often contains metal pipes that are excellent conductors of electricity.
If lightning strikes a house or the ground nearby, the electrical current can travel along these metal pipes and into the bathroom. Even in homes with modern plastic piping, running water acts as a sufficient electrical conductor, connecting a person in the shower to metal fixtures like faucets and the showerhead. While modern grounding systems are designed to safely direct the charge into the earth, a direct or nearby strike can still induce dangerous voltage surges. Standing in a shower or bath provides a direct pathway for this energy surge, increasing the risk of electrocution.
Other Indoor Hazards During a Storm
The mechanism of lightning traveling through utility systems makes several other common indoor activities hazardous during a thunderstorm. Any activity involving contact with plumbing should be avoided, including washing hands, doing laundry, or washing dishes in the sink. These actions place a person in contact with water and metal fixtures that can carry a dangerous electrical charge.
Similarly, corded electronic devices pose a risk because they are connected to the home’s electrical wiring, another primary conduit for lightning surges. Using a corded landline phone, a computer plugged into a wall outlet, or any appliance like a washing machine or dryer should be stopped immediately. Lightning-induced power surges can travel through the electrical system, potentially causing injury to anyone touching the device or its cord. Contact with exterior structures, such as metal window frames, metal doors, or concrete floors and walls containing metal rebar, should also be avoided, as these can conduct a charge from a strike.
Knowing When the Danger Has Passed
Determining when a thunderstorm is no longer a threat is essential for safely resuming activities like showering or using corded electronics. The general safety guideline followed by experts is known as the 30/30 rule, which begins when you first hear thunder.
The first “30” means that if the time between seeing a lightning flash and hearing thunder is 30 seconds or less, the storm is close enough to be dangerous, and you must seek shelter. Once safely indoors, the second “30” dictates the waiting period. Wait 30 minutes after the last observed flash of lightning or clap of thunder before leaving shelter or using water and corded appliances. This extended waiting time accounts for lightning striking up to 10 miles away, ensuring trailing parts of the weather system do not pose a surprise hazard.