ALBUQUERQUE, N.M. (AP) — Researchers at one of the nation's federal laboratories are creating simulated lightning as part of an effort to determine how everything from nuclear weapon components to entire buildings will hold up to Mother Nature.

They're building upon what is already known about the physics of lightning to make sure the blast of energy released by a strike doesn't affect sensitive areas of a weapon, said Larry Schneider with Sandia National Laboratories' electrical sciences group.

"Sandia's primary mission is to assure an 'always/never' operating condition for nuclear weapons. They must work when authorized and never function otherwise," he said. "Direct strike lightning is a threat in the 'never' scenario."

Sandia's lightning simulator has been performing tests since the 1970s, but officials say the focus now is on improving the understanding behind lightning and the ways it interacts with various systems.

Researchers are looking at how lightning flows through lattices of rebar and what kind of electromagnetic forces are generated when protective wiring is exposed to currents that would be equivalent to a lightning strike, or as much as 200 kilo Amps.

A lightning strike can last a quarter of a second, but the effects can linger. Through computer modeling and testing in the simulator, researchers can ensure that small components, subsystems and nuclear weapon systems meet requirements whether lightning directly strikes the weapon, the missile or the aircraft that carries it.

Tests can also be done to mimic lightning strikes that are nearby and generate electromagnetic fields.

Leonard Martinez of Sandia's electrical science and experiments group said most of the tests are done on pre-fabricated samples of reinforced concrete walls. However, researchers also measure currents at locations in the lattice without the surrounding concrete to better understand how the energy might be distributed in a realistic situation.

The test results are being compared to modeling so researchers can calculate expected forces on protective wiring assemblies.

High-speed cameras are helping to capture what's happening.

Sandia's simulator creates a lightning pulse — like a massive jolt of static electricity — by discharging high-voltage generators. A continuing current can be injected between pulses, much like natural lightning.

The lab does 200 to 300 tests a year, and Martinez said operators can fire the machine several times a day. It fits into a large room that includes diagnostic recorders, fiber optic transmitters and walls that can filter out electromagnetic waves.

Aside from helping to ensure the safety of the nuclear stockpile, the simulator also was used following a deadly 2006 explosion at a West Virginia coal mine. The federal Mine Safety and Health Administration asked Sandia to study whether energy from a lightning strike could travel underground to ignite an explosive mixture of gas trapped in a sealed section of the mine.

After spending days at the site, a team from Sandia determined that current from a surface strike can generate electromagnetic fields that spread through the earth. The findings were part of mining agency's report to Congress.