Level 4 airlock door rule

The Level 4 airlock door rule was a basic barrier against contaminated air moving from the hot area of the Reston monkey house into the staging area. During the Army’s response to the outbreak, the rule was applied in a makeshift airlock: its two doors were to remain closed one at a time, never open together.

Purpose and Principle

The rule controlled airflow at the boundary between contaminated and cleaner work areas. Opening both doors at once could allow contaminated air to flow back toward the staging room, where personnel prepared and entered their protective equipment. Keeping one door closed while the other was used preserved a physical separation between the two spaces.

The Makeshift Airlock

Gene Johnson reconnoitered the building to plan how the response team could enter and where to establish an airlock and gray zone. An empty storeroom became the staging area, and a closed corridor leading farther into the monkey house was designated as the airlock. The arrangement used existing rooms rather than a purpose-built passage. Johnson also had workers seal a door leading to the back monkey rooms with military tape, intending to reduce the movement of contaminated air toward the building’s offices.

When Jerry Jaax and Captain Mark Haines entered, they moved through the dark corridor between the staging area and the hot zone. They had no flashlight, so they felt their way along the walls to the far door. The physical difficulty of the entry did not change the rule: the two airlock doors could not be open at the same time, lest contaminated air flow back into the staging area.

Limits and Significance

The airlock rule depended on the building’s routes being understood and controlled. During the entry, Jaax and Haines encountered two Hazleton workers who had reached the back area by another route, despite the effort to seal access. The workers wore respirators but had no eye protection. Their presence revealed a weakness in the wider containment arrangement: controlling the airlock doors could not by itself prevent access through an unrecognized path.

The rule therefore functioned as one safeguard within a larger, improvised system of barriers, sealed doors, protective suits, and controlled entry. Its significance lies in both its simplicity and its limits: a clear door procedure reduced one route for contaminated air to move, but depended on the team also identifying and managing every other route into the hot area.