Since Aberdeen Proving Ground cleared a stockpile of deadly mustard agent last year, the distant booms of guns and occasional flashes of light have been the only reminders of the weapons testing taking place beyond the gates of the sprawling military base.
But in two separate yet strikingly similar incidents this week, the reality of APG's dangerous mission resurfaced when power failures in a pair of chemical testing laboratories prompted concerns that employees could have been exposed to deadly substances when ventilation fans failed.
No one was injured, but more than a dozen workers faced potential exposure to fumes from some of the nastiest poisons that might be used in warfare - including nerve agents such as GB and VX.
Officials have begun reviewing the electrical wiring of laboratory buildings - as well as the ventilation systems of their chemical testing chambers - in search of an explanation for the outages. In both cases, powerful fans that pull dangerous vapors away from researchers temporarily failed because of electrical problems.
"It certainly has raised a lot of questions," said Timothy J. McNamara, APG's director of safety, health and environment. "They were unrelated operations - in two different buildings - with two unrelated electrical circumstances; however, both resulted in the [ventilation systems'] closing."
George Mercer, a spokesman for APG, said there is no reason to believe the incidents were anything other than a coincidence.
He said that although two employees sought off-post medical treatment Tuesday, both were released the next day.
None of the employees involved in Wednesday's incident showed symptoms of exposure, Mercer said.
"We have them," Mercer said of laboratory accidents. "But when dealing with highly technical, complex operations, there is a follow-up, and many, many forces go to work at finding out what happened."
Established in World War I to test artillery and ammunition, APG is set to become further entrenched as a center of weapons testing as a military realignment shifts thousands of jobs to the base.
Its relationship with neighboring residents, however, has at times been shaky, with concerns over unexploded munitions and hazardous wastes buried under ground.
Last year, the last of a 1,600-ton stockpile of mustard agent was cleared, though the Edgewood area remains a center of chemical weapons research, testing and development.
Arlen Crabb is a longtime environmental activist in the community and a member of the Restoration Advisory Board at APG.
He is scheduled to visit APG today for a site inspection, he said.
"I'm kind of concerned, a little bit," Crabb said, particularly because the events happened twice in two days. "Some of the buildings ... they're kind of close to the housing areas or other areas where people aren't protected."
More than 4,000 military personnel and family members live on the post, and many more civilians live in homes just off the base.
There were at least two incidents last year involving chemical agents that prompted a response from APG officials. Last April, a cylinder of hydrogen cyanide - a volatile, hazardous chemical - burst in a storage cabinet.
A month earlier, two employees had been were taken to Upper Chesapeake Medical Center for possible chemical exposure to phosgene, a choking agent.
Harford County Councilwoman Cecelia M. Stepp, whose district includes much of the land adjacent to APG, said base officials are forthcoming about incidents.
"They have always gone out of their way to calm any fears that would be felt throughout the community," she said.
On Wednesday, a power surge reported just before 2 p.m. affected four laboratories in the Edgewood Chemical Biological Center, where three employees were working with drops of liquid chemical warfare agents inside a laboratory box that has an electrically powered ventilation system.
The chemicals were mustard, a blistering agent; GB, a nerve agent; and two other poisonous chemicals, hydrogen cyanide and cyanogen chloride. The employees were treated on-post and released.
The previous day, 15 employees at the U.S. Army Medical Research Institute of Chemical Defense were working with mustard and nerve agent when the computer system that controls ventilation for the laboratory box malfunctioned, and two were taken to a local hospital for observation.
With such complex equipment in use, the notion that a power blip could endanger the lives of employees - and potentially, nearby residents - should be cause for concern, said Richard Ochs, a Baltimore resident and former member of a citizens' watchdog group.
"If they don't have enough redundancy in their safety electrical systems, if they don't have enough backup, that scares me," Ochs said.
A spokesman for the Maryland Department of the Environment said the agency would investigate.
"A lot of buildings on base have uninterruptable power," said Richard McIntire, a spokesman for MDE.