This week's question was submitted by Leigh. Thanks!

Q: If I were to direct a stream of water from my kitchen sink's dish sprayer into a nearby electrical outlet, I would be shocked or electrocuted. So, why aren't firefighters harmed when holding a hose and spraying a burning building?

Let me begin by saying I am not a scientist. One of the few things I remember about my high school physics class (when most of us learn about things like electricity) is having to construct a 14-inch tall tower entirely out of straight pins and drinking straws. The tower had to be able to support at least two of our physics textbooks. While I'm happy to report I was one of the best in the class when my tower withstood the weight of about a dozen books before collapsing, my drinking straw tower building abilities unfortunately don't help me here. That being said, this question can be approached in several ways.

Scenario One:
In the first scenario we will assume the electricity is still running while the firefighters are attacking the blaze. The two major lines of defense against any electrical shock are insulation and grounding. Insulators are materials, such as rubber, plastic or wood, that do not allow a charge to run through it. Electrical wires are insulated in rubber, and the handles of power tools are encased in plastic, to keep an electrical charge in the metal where it belongs. Pure, de-ionized water is also a good electrical insulator. Other types of water, such as tap or salt, only become conductant because of the other elements present in them.

Grounding, on the other hand, provides a release for a built up electrical charge in an object. Electricity is always trying to get to the ground because the earth has little resistance and allows electricity to expand as far as it can go. Electricity always take the path of least resistance, but it requires a complete circuit, a path from the power source to the ground, in order to flow.

With these simple principles in mind, we can try to form a hypothesis. First, fire hoses have a thick rubber core and are encased in a lining made from cotton (another insulator) or some other fiber. The insulating rubber may protect against shock. Second, firefighters wear boots with heavy, insulating soles that may also provide some resistance, denying an electrical current a path to the ground, and protecting them from shock (unless they're standing in a pool of water). This argument, however, seems pretty weak.

Scenario Two:
Buildings are wired and electrical equipment is installed according to standards set by the National Electric Code. The current that any wire can carry safely is limited by its thickness and insulation because every wire has resistance and converts some of the energy it carries into heat. A thick wire can safely carry more current because its larger surface area provides less resistance and helps dispose of more heat. However, the wire does still produce heat and must be protected against overload. An overloaded electrical circuit is carrying too much current. The wires can become dangerously hot, which may melt the wires and set fire to the building.

To protect a home from overloaded circuits, every circuit includes a built-in weak link, such as a fuse or circuit breaker. A fuse is simply a piece of thin, tin-plated copper wire or other piece of metal with a low melting point. If too much current flows through the circuit, the fuse heats and melts, breaking the circuit. You must then find the problem, fix it and replace the fuse.

A circuit breaker serves the same function as a fuse but doesn't need to be replaced. When the curent gets too high, a switch opens and breaks the circuit. The switch can simply be reset after the problem is corrected.

Most accidental structural or residential fires are electrical in origin. But, even though fire was not prevented, if the fuse or circuit breaker is doing its job, electricity will be shut off to the damaged circuit. Therefore, with the circuit broken, electrocution is not an issue as the firefighters attack the blaze.

Scenario Three:
I've presented a poor hypothetical scientific explanation and a half-hearted electrical wiring explanation, but this is the scenario for which I found the most evidence. Again and again, I found that, as a matter of procedure, power is shut off to burning buildings in order to remove the danger of electrocution while putting out the fire.

Expect the worst. There is no such thing as a routine emergency. These are the mantras of the firefighter. In a profession where 1 out of 7 is injured or killed on the job every year, firefighter safety is taken very seriously. The website of Vincent Dunn, a retired deputy chief of the F.D.N.Y., has an excellent summary of the procedures followed to shut off electricity to a burning building. Firehouse Magazine is another great resource if you want to read first-hand accounts of firefighting tactics. I found dozens of stories that included evidence of the power being cut at the scene of an emergency either by trained firefighters or by the local utility company.

I apologize if, by avoiding a complicated scientific explanation, this isn't the answer you expected, but the truth is that electrocution does pose a real danger to firefighters. They recognize this fact and have safety procedures in place to protect themselves on the fireground. Thanks again for submitting this question and giving me a chance to learn about fire fighting tactics. My respect for the profession has increased tremendously as a consequence of the reading I did to write this column.

Coincidentally, this week is also Fire Prevention Week, the country's "longest running public health and safety observance." President Woodrow Wilson issued the first National Fire Prevention Day proclamation in 1920, and, since 1922, National Fire Prevention Week has been observed during the week in which October 9 falls. Why October 9? The date was chosen in commemoration of the Great Chicago Fire of 1871 which, though it began on October 8, continued to burn and inflict the most damage on October 9. So, now that I've established the Chicago connection, stay safe, check those smoke detector batteries, and come back next week because for the rest of October I'll be scaring up some fun facts about famous dead and haunted places in Chicago.

Additional Resources
Angle, James. et.al. Firefighting Strategies and Tactics. Albany, NY: Delmar, 2001.

Cole, Arthur E. Fire Protection Handbook. 18th ed. Quincy, MA: National Fire Protection Agency, 1997.

Montagna, Frank C. Responding to 'Routine' Emergencies. Saddle Brook, NJ: Fire Engineering Books & Videos, 1999.

Got a question? Go on. Ask me. I dare you. Send your questions to librarian@gapersblock.com and it may be featured in a future column.

Next week: The brother of Charles Dickens buried in Chicago.