During a toxic gas incident, what is essential to do before evacuating?

Setting all structural boundaries is crucial during a toxic gas incident as it helps contain the toxic substance within a designated area, minimizing its spread and protecting both personnel and the environment. Establishing these boundaries can include sealing doors and windows, closing vents, and using barriers to prevent the toxic gas from escaping into other areas where people may be present. This containment step is fundamental to preventing further exposure and ensuring that evacuations can be conducted safely without the risk of inhalation or contact with hazardous materials.

In contrast, activating the fire suppression system may not be appropriate if the incident does not involve a fire, while ensuring no crew is on deck is important primarily for safety but does not address containment. Checking all equipment, while useful for preparedness, doesn't directly contribute to immediate safety measures in the context of a gas leak. Thus, focusing on structural boundaries is a proactive measure critical for effective incident management.