Section 309 establishes Group M occupancies as buildings or portions thereof for the display and sale of merchandise and related public interaction. Mercantile occupancies include retail stores, shops, department stores, shopping malls, gas stations, and other sales environments. Occupant load for mercantile spaces is calculated at one person per 30 square feet of gross floor area, accounting for customer circulation and browsing areas. Sales areas with dense merchandise display may have higher occupant loads. Two exits are required for occupant loads exceeding 50, with specific egress width requirements based on occupancy load. Travel distance in mercantile occupancies is limited to 250 feet in sprinklered buildings or 200 feet in non-sprinklered buildings. Egress from storage areas and employee work areas must be provided with separate exits from customer areas where practical. Fire-resistance-rated walls are required between mercantile and other occupancies. Outdoor sales areas such as gasoline dispensers must have specific separation from buildings. Interior finishes in sales areas and corridors must meet flame-spread ratings. Sprinkler systems are typically required in mercantile buildings exceeding specified size thresholds. Paint booth areas used for finishing merchandise require specialized fire protection with specific sprinkler densities for Class III ordinary combustible loads.