Today's manhole fire in San Francisco caused a loss of power to approximately 8,600 PG&E customers and a shelter in place was ordered for people in the area as well.
The explosion and fire according to news reports were due to a PG&E equipment problem further impacted by about 75 gallons of oil in an oil switch.
No injuries were reported but emergency crews were kept busy by responding to people trapped in elevators caused by the loss of power.
Video from KRON4 of todays Manhole Fire:
Manhole fires are not as common here in the Bay Area as they are where I am originally from in NYC, since they usually occur during the winter and are most often caused by water and salt seeping into the manholes and corroding wires.
However there are many hidden dangers of manhole fires which are increased since the fire is happening underground and your not able to view the source of the fire directly.
First the biggest danger is the gases that these fires give off which include Carbon Monoxide (CO), Polychlorinated biphenyls (PCBs) and many others can actually travel through the underground systems and into the surrounding buildings.
It is often best to evacuate the surrounding buildings in large fires and or monitor the air quality in parts per million, especially since these gases are often orderless, colorless, and tasteless and by the time you realize you are exposed it may already be too late. I once had a police officer as a patient with CO poisoning that was left to watch on open manhole after a fire.
Once the fire is out, the danger of the gas still often remains and must be addressed.
The other danger is that manhole covers can range in weight from 150 pounds up to 300 pounds and the fires tend to burn unnoticed underground until significant pressure builds up causing the an explosion that often shoots the manhole cover sometimes as high as six stories into the air.
These manhole covers can sometimes be found several blocks away, on rooftops and sometimes land on top of passing cars.
One winter I was inside my EMS station in Brooklyn, NY restocking after a call, trying to relax on a busy winter day. I was in a room getting supplies when a huge explosion took place, rocking the building and caused me to literally jump.
My partner and I went outside and a car parked next to our station was on fire. The car was parked on top of a manhole that exploded and hit the gas tank. The car by the way was also parked next to the wall I was standing near. I was lucky it didn't damage the building but it was the loudest explosion I've heard, and the closest I ever was to an explosion.
So, try not to park on top of a manhole cover if you can avoid it.
The other danger is in the thick black smoke coming out of the manhole which is also highly combustible. The smoke is also not always black either depending on what is burning, I have seen bright red, dark red, yellow, and purple, each of which presents its own dangers since they add other toxic gases to the area.
For more on manhole fires please view the following links:
Fire In the Hole: The Causes and Effects of Manhole Fires
Another video of a Manhole Fire in NYC during winter
Excellent Video of Underground Transformer Fire below as well: