General Definition

• The minimum number of exits refers to the minimum required number of safe egress routes that must be provided in a building or space to ensure timely evacuation during emergencies.
  • Building codes establish these requirements based on occupant load, building size, use classification, and fire safety considerations to prevent overcrowding and improve life safety.
• The Building Standard Law of Japan (BSL) Chapter 5 governs required exits, considering occupancy type, building size, fireproofing measures, and evacuation planning.
  • The following is a comparative table integrating all aspects of means of exiting requirements for Group A-1 Occupancy under IBC Section 1006.3.2 and BSL Article 20 specific regulations:

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Means of Egress Aspect	IBC (International Building Code – USA)	BSL (Building Standards Law – Japan)
Occupancy Classification	Group A-1 (Assembly – Fixed seating for performance, e.g., theaters, concert halls)	Assembly Use Classification (劇場, 映画館, 集会所等)
Minimum Number of Exits	– 2 exits for occupant load ≤ 500 – 3 exits for 501-1,000 occupants – 4 exits for > 1,000 occupants (IBC 2018, Table 1006.3.2)	– 2 exits required for assembly use (BSL Article 20) – Additional exits required for large occupant loads based on layout and safety evaluation
Exit Width Requirements	– 0.3 inches (7.62 mm) per occupant for stairs – 0.2 inches (5.08 mm) per occupant for other egress components (IBC 2018, 1005.3.1, 1005.3.2)	– 90 cm (35.4 inches) minimum exit width (BSL Article 119) – 120 cm (47.2 inches) minimum for staircases in large assembly buildings
Corridor Width	– 44 inches (1118 mm) minimum (IBC 2018, 1020.2)	– 90 cm (35.4 inches) minimum (BSL Article 119)
Maximum Travel Distance to Exit	– 150 feet (45.72 m) (non-sprinklered) – 200 feet (60.96 m) (sprinklered) (IBC 2018, Table 1017.2)	– 30 meters (98.4 feet) (non-sprinklered) – 50 meters (164 feet) (sprinklered) (BSL Article 119)
Common Path of Travel	– 75 feet (22.86 m) (non-sprinklered) – 125 feet (38.1 m) (sprinklered) (IBC 2018, Table 1006.2.1)	– 20 meters (65.6 feet) (non-sprinklered) – 30 meters (98.4 feet) (sprinklered) (BSL Article 119)
Stairway Width	– 44 inches (1118 mm) minimum for occupant load > 50 (IBC 2018, 1011.2)	– 120 cm (47.2 inches) minimum for large assembly occupancies (BSL Article 119)
Minimum Ceiling Height	– 7 feet 6 inches (2286 mm) minimum (IBC 2018, 1003.2)	– 2.1 m to 2.3 m (6 feet 10 inches to 7 feet 6 inches) minimum depending on function (BSL Article 28)
Exit Signage & Emergency Lighting	– Required in all assembly occupancies (IBC 2018, 1013, 1008.3)	– Required in all assembly buildings (BSL Fire Code Enforcement Regulation Article 126)
Fire Resistance for Exit Enclosures	– 1-hour fire rating for ≤ 3 stories – 2-hour fire rating for > 3 stories (IBC 2018, 1023.2)	– 1-hour fire rating for ≤ 3 stories – 2-hour fire rating for > 3 stories (BSL Article 35, Fire Service Law)
Egress Doors Requirements	– Minimum 32 inches (813 mm) clear width – Must swing in the direction of egress travel for occupant load > 50 (IBC 2018, 1010.1.1, 1010.1.2.1)	– Minimum 80 cm (31.5 inches) clear width – Must swing outward for large occupancy (BSL Article 119, Fire Safety Regulations)

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• IBC strictly mandates a minimum number of exits based on occupant load, whereas BSL allows adjustments based on safety evaluations and layout.
• IBC allows longer travel distances (200 feet/60.96 m) in sprinklered buildings, whereas BSL has stricter limits (50 m/164 feet max).
  • BSL enforces a minimum stair width of 120 cm (47.2 inches), which is wider than IBC’s 44-inch (1118 mm) minimum requirement.
• Both codes require emergency signage, fire-rated enclosures, and outward-swinging doors for large occupancies.
  • BSL has a slightly lower ceiling height requirement (2.1 m vs. IBC’s 7 feet 6 inches).

Recommendations for Improving

• IBC (USA)
  • Increase minimum stair width to 120 cm (47.2 inches) for better evacuation flow.
  • Reduce maximum travel distances (especially for sprinklered buildings) to enhance fire safety.
  • Mandate two exits for basement assembly spaces, even for small occupant loads.
  • Increase egress door width to 900 mm (35 inches) for better accessibility.
  • Require a 2-hour fire rating for all large assembly exit enclosures, regardless of height.

• BSL (Japan):
  • Set a strict 4-exit requirement for >1,000 occupants (instead of layout-based flexibility).
  • Allow slightly longer travel distances in fully fire-protected buildings.
  • Increase stair width to 150 cm (59 inches) for assemblies over 2,000 occupants.
  • Increase corridor width to 100 cm (39.4 inches) for smoother egress flow.
  • Strengthen fire resistance requirements for high-occupancy buildings, even if low-rise.

Summary

• Align global standards for easier international compliance.
• Introduce performance-based egress design solutions.
• Encourage smart evacuation systems with AI-driven emergency signage.
• Strengthen universal design principles for improved accessibility.