When John Spradling had window film installed in his Oklahoma City real estate office, he did so with the hopes of saving on energy.

But when the Alfred P. Murrah Federal Building was bombed six blocks from Spradling's office, the film protected him from more than a high electricity bill -- it held together shards of glass that may have flown from the window, injuring or killing him. That day in 1995, 800 others in the area suffered injuries from glass, some of them sustained in buildings 18 blocks from the blast.

"I was facing a window that blew out," Spradling said. "There's no doubt in my mind the glass would have blown into my office."

Terrorist attacks including the Oklahoma City bombing and those of Sept. 11, 2001, have spawned increased sales of security window film -- clear or tinted sheets made of polyester and sometimes metals -- applied to windows to prevent breaking glass from explosions and burglaries. In the Washington area, companies are struggling to keep up with the high demand for installation, a demand that intensified after this weekend's terror alerts.

Troy Vlahos, vice president of business development with Baltimore's Energy Management Systems, said the company's phone was ringing steadily yesterday morning, after the federal government raised the terror alert level to orange for the financial services sectors in New York, Washington and Newark.

"With the recent news, we've been hearing feverishly from our clients," Vlahos said. "We heard from a world organization in Washington, D.C., one financial institution, a federal agency and an out-of-state military base."

After the Oklahoma City bombing and the embassy bombings in Africa, the federal government began requiring the film installation on some federal buildings. But after Sept. 11, mainstream commercial buildings also began buying.

"It's essentially a new industry," said Jim Hondroulis, president of Energy Management Systems, which installs security film in the District.

Darrell Smith, executive director of the International Window Film Association, said that prior to the terrorist attacks, sales of security film accounted for 1 to 3 percent of all window film sales, which includes films used for tinting and blocking UV rays. But today, security film accounts for as much as 15 percent of window film sales -- a $1 billion-a-year industry.

There are several types of window film -- decorative film, security film and film that blocks sun and UV rays on buildings and cars. Security film applied to standard commercial plate glass causes it to act similarly to car window glass, which breaks into small pieces rather than dangerous sharp shards. It provides the highest level of protection, but the others may slightly reduce shattering.

Jeff Bradley, U.S. and international business manager for 3M, a security film manufacturer, said terrorists are using glass as a weapon.

"In the embassy bombings in Africa, there were two bombs -- first was a small bomb that drew everyone to the window, then the second one went off and caused all of the damage because of the glass," Bradley said, noting that glass injuries are difficult to treat because the glass is hard to find.

And those injuries can be fatal. Following the 1996 terrorist bombing in Saudi Arabia, a Pentagon report found that 12 of the 19 airmen killed died as a result of glass-cut injuries.

Smith said consultants often will assess a building's risk to determine its needs and risk factors, including how likely a target the building is and proximity to parking lots.

"If the windows are near a parking lot, they may need stronger treatment because someone could put a car bomb there," Smith said, noting that cars and trucks can carry bombs weighing up to 1,000 pounds, whereas a person with a bomb strapped to the body could carry roughly 100 pounds.

Hondroulis said security film is a start, but not a guaranteed solution for safety in the event of a bomb.

"If a bomb blast is big enough and close enough, you are out of luck," Hondroulis said. "But if the blast is six blocks away, the window that would have been blown out is still intact."

In the District, customers include embassies, federal buildings, corporations and retailers, which install the film to deter "smash and grab" robberies.

Scott Haddock, president of GlassLock Inc., which installs the film internationally, said 98 percent of the company's U.S. business comes from federal government contracts. The company has installed film in government agencies including the Department of Defense, the General Services Administration and the State Department.

Federal regulations -- established in 1997 by the GSA -- specify that glass can crack but must be retained by the frame when subjected to a blast equivalent to 500 pounds of TNT.

Haddock said security film has been popular in Europe and was widely installed in the 1970s during the Irish Republican Army bombings in Britain. But with the growing threat of terrorism, the film has become popular in the United States.

"Here in the States it wasn't used so much -- we just weren't experiencing the type of problems we have nowadays," Haddock said.

And the Washington area, with its high concentration of government buildings, is a prime spot for growth. Area contractors who install the film say business has soared. Security film sales at GlassLock have grown tenfold since Sept. 11, according to Haddock.

At Energy Management Systems, sales have increased by more than 60 percent. Hondroulis said there's so much business, he has had to call in workers from other regions to help handle it.

And in March, contractor Utah Security Specialists expanded operations to the Washington area because of its high demand.

"It's a very highly populated, security-conscious area," said Pat McBride with Utah Security Specialists.

CPFilms, a security film manufacturer with eight distributors in the Washington area, says its sales have increased 25 percent since Sept. 11. Contractors say demand for the film is also high in New York.

The film, which varies in thickness, costs from $4 to $10 a square foot to apply, depending on the size and accessibility to windows and whether the film is being attached to the glass or the frame. With the addition of a thin metal coating, security film can also save energy by reducing solar heat entering the building.