Indoor carbon monoxide exposures in a retail occupancy

In a two-story retail mall in the Southeastern United States, employees within Store A (located on the second level) began to feel headaches and general unease and discussed the symptoms among themselves. Approximately 1.5 hr later, an employee called 9-1-1. Upon arrival, the fire department discovered the presence of carbon monoxide (CO) within Store A and evacuated all employees and customers. As a result of this incident, 13 employees were treated for carbon monoxide poisoning that day, and an additional four employees sought medical attention in subsequent days. This work discusses the events leading up to this incident, which involved welders used for indoor construction on the first level of the mall inside Store B-situated directly below and adjacent to Store A's east wall. It was determined that carbon monoxide was created by the use of liquified petroleum gas-fueled (LPG) welders on the first story of Store B, which migrated into Store A through unsealed floor penetrations within floor electrical receptacles. From the identified causes, this work proposes strategies to reduce the likelihood of similar incidents occurring in the future.