Coins might drop through the holes, but exploding gases are unlikely to blast manhole covers into the air like they did last winter in Georgetown and other sections of the District of Columbia.
Potomac Electric Power Co. employees yesterday began installing the new cast-iron covers, each weighing less than 100 pounds, over manholes in Georgetown.
Each cover, 24 inches in diameter, has 218 slots that will allow smoke, a sign of danger, to escape from the manhole. If manhole gases ignite and explode, the pressure will escape through the slots instead of propelling the cover into the air.
After underground explosions last winter sent flames and antiquated covers into the air above Georgetown and other D.C. streets, experimental covers were tested in Massachusetts.
No one was injured by the blasts, and Pepco General Manager William “Bill” Gausman promised that if the Massachusetts tests proved new covers were safer, they would be installed in the District.
“Testing of the slotted covers showed that their use should minimize the frequency and impact of manhole cover displacements,” Pepco Vice President Robert C. Grantley said yesterday as the first new cover was installed on Water Street near Whitehurst Freeway NW in Georgetown.
Pepco has 3,000 of the new slotted covers and expects to install 1,000 of them by the end of the year. They will go in heavily traveled pedestrian areas and crosswalks from Georgetown through the District’s business section to Capitol Hill.
“We cannot guarantee that underground electrical problems will be totally eliminated with the installation of the slotted covers,” said Mr. Grantley. “However, we can assure you that we are responding aggressively at several levels to ensure our system is as safe and reliable as possible.”
Company officials said more manholes will be inspected to spot and fix potential problems before the smoking begins. The company is scheduled to inspect 10,000 of the city’s 57,000 manholes per year.
Last winter, salt, sand and snow-melting chemicals often were blamed for eroding cable covers that caused electrical shorts. The resulting heat caused smoke, which sometimes was seen as a warning of impending fire and/or explosion.
“Should cable faults occur that result in smoke, the slotted covers would permit the smoke to disperse and facilitate early warning and detection,” Mr. Grantley said.
Old age may have deteriorated cables under historic Georgetown to cause explosions there. On Feb. 18, three manhole covers erupted in Georgetown and several businesses had to close for the weekend.
Pepco officials said an engineering consultant group has been hired to assess the entire system to determine if other improvements should be made.
Also, Pepco said it is working with the District’s Emergency Management Agency to increase training for contractors who dig in city streets to help them avoid cutting into electric lines.
Pepco workers will install the new covers during off-peak hours to minimize disruptions of rush-hour traffic. The new covers are rust-colored, but weathering will turn them grayish like the old covers.
A task force of consumer groups, city agencies and utilities, assembled by Mayor Anthony A. Williams, had recommended more inspections and system corrections after more than 20 manhole incidents. Other cities in the U.S. Northeast have experienced similar problems.