Cargo Characteristics, Hazards, and Compatibility
Know the data source
Cargo hazards are defined by the safety data sheet and the relevant compatibility and segregation guidance. Candidates must understand flash point, vapor pressure, vapor density, solubility, and reactivity - and how each drives a control measure. Flash point determines flammability class; vapor density determines whether vapors collect low or disperse; vapor pressure drives venting and inerting needs.
Compatibility and segregation
Incompatible cargoes must be segregated so that a leak or rupture cannot bring them together. Understand that segregation is about physical separation and independent systems, not just tank adjacency. Questions often test whether two products can share a common vent, a common line, or a common pumproom.
Common traps
- Treating a high flash point as "safe" - heated cargo can be above its flash point.
- Confusing lower and upper flammable limits; the range between them is where ignition occurs.
- Assuming vapors are heavier or lighter than air without checking the product.
- Forgetting oxygen deficiency in enclosed spaces and inerted tanks.
- Overlooking reactivity with water, air, or common materials.
Worked rule of thumb
Vapor density relative to air near 1.0 means poor dispersion; above 1.0 means vapors settle into low spaces such as pumprooms and bilges. If vapor density is greater than 1, treat low spaces as hazardous and ventilate and monitor before entry. Always confirm with the SDS rather than memory.