In a raceway that provides communication between a dust-ignitionproof enclosure and one that is not, what must be prevented from entering through the raceway?

In a raceway designed for communication between a dust-ignitionproof enclosure and a non-dust-ignitionproof enclosure, it is crucial to prevent dust from entering the raceway. Dust can be a significant ignition source in hazardous locations where dust particles are present, especially if they become airborne and are mixed with a sufficient concentration of air. The ingress of dust into areas where electrical equipment is housed can potentially lead to increased risk of ignition or explosion.

Dust-ignitionproof enclosures are specifically designed to contain any ignition sources within them and protect the environment outside from dust ignition hazards. Ensuring that dust does not enter through the raceway maintains the integrity of the protective measures in place. This is particularly important in industries where combustible dust is prevalent, as a small amount of dust entering the equipment can create hazardous conditions.

While water, gas, and vapors also present risks in specific scenarios, the primary concern in this context is dust, as it directly relates to the enclosure's ability to manage and contain ignition risks associated with combustible materials.