ABERDEEN -- Two lab workers were taken to a hospital for observation today for possible exposure to a choking agent in an Aberdeen Proving Ground laboratory, according to a base spokeswoman.

Researchers, unaware that maintenance workers were testing the building's filter system, were running an experiment using the agent phosgene, said Joan Michel, a spokeswoman for the Edgewood Chemical Biological Center. An alarm sounded when the ventilation system switched off and the lab workers returned to shut down the experiment, she said.

Three lab workers and two maintenance workers who were outside the building were taken to the Edgewood Area Clinic for observation and evaluation, Michel said. None showed signs of exposure, but since symptoms can sometimes take up to 48 hours to appear, two lab workers were taken to Upper Chesapeake Medical Center for further observation, she said.

Michel said the lab workers were testing protective gear's resistance to the chemical. A breakdown in communication led to the incident, she said. Supervisors in the building are notified of routine maintenance by e-mail.

The chemical was not detected outside the ventilation hood where the chemical was being used and there was no release outside the facility, officials said.

Phosgene is used to make plastics and pesticides and in industrial processes such as dry cleaning. It was also used extensively in World War I, causing the majority of chemical-related deaths, according to the Centers for Disease Control and Prevention.