NEW YORK — THE explosion of a gas line in midtown Manhattan earlier this month set off a spectacular fire that took six hours to quash. Yet the break rated no mention in major local newspapers. The drilling that goes on in almost every block to repair anything from broken sewer lines to steam pipe leaks and the 550 annual breaks in city water mains similarly are treated as nonevents.
It's a sign of just how routine breaks and repairs have become in the aging underground labyrinth of pipes and wires that make this city work.
New Yorkers seem to notice only when either vital services are cut or when many residents are routed from their homes - as in the 1989 blast of asbestos-coated steam pipes in Grammercy Park.
Though New York City has the nation's largest and most complex underground system, one that includes even electrical and phone wires, all older Frostbelt cities of the Northeast and the upper Midwest share problems in common.
Their subterranean wires and pipes are close together and have been in place a long time. They shift as underground water freezes and thaws and as subways rumble underneath.
Much as cities might like to replace all older water or sewer lines at the same time, all have settled for the less disruptive hit-and-miss pattern of piecemeal breaks and repairs.
Often problems in one pipe lead to problems in another. Dick Netzer, an economics professor with New York University's Robert F. Wagner Graduate School of Public Service, says that in excavating it may become necessary also to move another agency's pipes or lines. ``You may end up doing a lot you didn't plan on doing,'' he says.
Mr. Wagner vividly recalls the time a couple of years ago when a water main broke near his home in Brooklyn. As workers tried to repair it, a gas main ruptured. Both gas and water service had to be shut off. Once it was restored, more leaks developed in both lines. ``That was not unusual,'' he insists.
Indeed, the Grammercy Park explosion occurred when Consolidated Edison was turning back on a gas line that had been temporarily closed to protect a nearby water main.
Sometimes utilities and city agencies mistakenly cut one another's lines.
Once in a while they inadvertently cut their own as an AT&T work crew did two months ago, depriving New Yorkers of long-distance service for more than three hours.
Still, there are signs of a growing effort by city and private utilities to develop a more orderly, coordinated approach.
Any major street dig is now likely to include repairs by all agencies with future maintenance plans at the cite.
Most cities have kept markedly poor records of their underground activities over the years. Many now are taking a more careful inventory of their stock and rates of repair. More frequent inspections often pinpoint leaks and ward off breaks.
Consolidated Edison checks all 1,800 of its steam manholes in New York City twice a year. ``Unfortunately we can't anticipate every single thing that happens, but we've made a lot of improvements since Grammercy,'' says company spokeswoman Rosalie Zuckerman.
The ability to predict where and when breaks in pipes and lines will occur is slowly becoming more of a science.
``I think we're going to get better at it because the risks are getting bigger,'' notes David Marks, chairman of the Department of Civil Engineering at Massachusetts Institute of Technology. His own research on water has exposed at least one myth: that older pipes perform poorly. ``We've got some really old pipes in the Northeast that are doing just fine,'' he says.
Small TV cameras can now be placed inside most pipes to check for conditions.
Several cities use small electronic listening devices to check for underground water leaks.
Dr. Marks says that Boston, which in the past has lost as much as one-fourth of its water supply to leaks, has done ``tremendously well'' in controlling and preventing breaks with the help of such devices. New York City, which hopes to replace all water mains built before 1930, has also made gains, according to city officials.
Still, engineers cannot yet know with any degree of certainty where and when underground line breaks will occur, insists Eric Lui, an assistant professor of civil engineering at Syracuse University.
``There's a lot of experimentation going on, but you can't monitor everything at the same time.... There are no magic answers,'' he says.