Building codes and structural engineering principles categorize loads as direct forces (mechanical loads) or indirect effects. Wind, dead loads, and earthquake forces are all direct mechanical loads that the structure must be designed to resist. Wind exerts pressure, dead loads are gravitational forces, and earthquakes induce inertial forces. Fire, in contrast, is a thermal event. It is not a direct mechanical force; instead, it subjects the structure to thermal loads (heat), which degrades the mechanical properties (e.g., strength, stiffness) of structural materials, potentially leading to failure under the existing mechanical loads.

B. Wind forces: Wind creates direct positive and negative pressure on the building envelope, which is a primary lateral force considered in structural design.

C. Dead loads: These are the static, permanent gravitational forces from the weight of the building's own structural elements and fixed components.

D. Earthquake forces: Ground motion during an earthquake induces inertial forces (Force = mass × acceleration) within the structure, which act directly on the structural system.

1. SFPE Handbook of Fire Protection Engineering, 5th Edition. Chapter 7, "Structural Fire Engineering," Section 7.2, "Fire as a Load on Structures." The text states, "Fire is not a load in the traditional structural engineering sense of an externally applied force or pressure... Instead, fire is a source of energy that results in a thermal load on the structure." (p. 189).

2. NFPA 5000®, Building Construction and Safety Code®, 2021 Edition. Chapter 35, "Structural Design," Section 35.3, "Load Combinations," lists dead, live, wind, and earthquake loads as forces to be combined for design. Fire is addressed separately as a condition affecting material resistance in Chapter 8, "Fire-Resistive Materials and Construction," not as a direct force in load combinations.

3. Hurley, M. J., et al. (Eds.). (2016). SFPE handbook of fire protection engineering (5th ed.). Springer. Section 1, Chapter 7. This reference further clarifies that the primary effect of fire is the elevation of temperature, which causes thermal expansion and degradation of mechanical properties, rather than applying a direct external force. (DOI: 10.1007/978-1-4939-2562-4).