Section 3.4: Flammable and Combustible Liquids

Classifying, storing, and handling flammable and combustible liquids is a critical aspect of fire plans examination due to their high energy density, volatility, and ability to spread fire rapidly. Under the 2024 International Fire Code (IFC) Chapter 57, these liquids are regulated based on their physical properties: flash point and boiling point. A plans examiner must evaluate storage configurations, maximum allowable quantities (MAQs), safety cabinets, tank systems, piping, and dispensing operations to ensure compliance.

Liquid Classification System

The IFC divides these liquids into two major categories: Flammable Liquids (Class I) and Combustible Liquids (Classes II and III). This distinction is critical because it dictates construction, electrical classification, and containment requirements for the storage or use area.

• Flammable Liquids (Class I): Liquids with a closed-cup flash point below 100°F (38°C). Subdivided as:
  • Class IA: Flash point below 73°F (23°C) and boiling point below 100°F (38°C) (e.g., diethyl ether).
  • Class IB: Flash point below 73°F (23°C) and boiling point at or above 100°F (38°C) (e.g., gasoline, acetone).
  • Class IC: Flash point at or above 73°F (23°C) and below 100°F (38°C) (e.g., xylene).
• Combustible Liquids (Classes II and III): Liquids with a closed-cup flash point at or above 100°F (38°C). Subdivided as:
  • Class II: Flash point at or above 100°F (38°C) and below 140°F (60°C) (e.g., diesel fuel, kerosene).
  • Class IIIA: Flash point at or above 140°F (60°C) and below 200°F (93°C) (e.g., heating oil).
  • Class IIIB: Flash point at or above 200°F (93°C) (e.g., motor oil, lubricating grease).

Maximum Allowable Quantities (MAQs) and Storage Cabinets

Under IFC Table 5003.1.1(1), baseline storage MAQs for flammable and combustible liquids are limited (e.g., 30 gallons for Class IA, 120 gallons for Class IB, IC, and II). The code permits these baseline quantities to be increased when specific systems are provided:

1. Sprinkler Increase: A 100% increase (multiply by 2) is permitted if the building is sprinklered throughout (NFPA 13).
2. Cabinet Increase: A 100% increase (multiply by 2) is permitted if the liquids are stored within approved cabinets.
3. Compounded Increase: If both sprinklers and cabinets are present, these increases are cumulative (multiply by 4). For Class IB, the 120-gallon baseline increases to 480 gallons.

Storage Cabinet Design and Construction (IFC 5704.3.2)

Plans examiners must verify that storage cabinets comply with capacity and construction limits:

• Capacity Limits: Class I and II liquids are limited to 60 gallons (227 L) per cabinet. Class III liquids are limited to 120 gallons (454 L) per cabinet.
• Cabinet Limit per Control Area: No more than three cabinets are permitted in a single control area, unless the area is designed as a Group H occupancy.
• Construction: Metal cabinets must be double-walled steel (minimum 18-gauge) with a 1.5-inch (38 mm) insulating air space. Sills must be raised at least 2 inches (51 mm) to create a liquid-tight sump.
• Venting: Venting is not required by the IFC. If vented, the vents must be piped directly to the outdoors using steel pipe. Otherwise, vent openings must be sealed with bungs.

Tank Storage (ASTs and USTs)

When liquid quantities exceed cabinet limits, bulk storage tanks are utilized:

• Aboveground Storage Tanks (ASTs - IFC 5704.2.9): ASTs must be separated from property lines and buildings in accordance with IFC Tables 5704.2.9.6.1(1) through (6). UL 2085 protected aboveground tanks allow for reduced separation distances. Secondary containment (diking or double-walled design) is required. Overfill protection must include an alarm at 90% capacity and an automatic shutoff valve at 95% capacity.
• Underground Storage Tanks (USTs - IFC 5704.2.11): USTs must be located at least 1 foot from basement walls or property lines. They must be buried under at least 1 foot of earth plus a concrete slab, or 2 feet of earth alone. They require double-walled construction, interstitial leak monitoring, overfill prevention (automatic shutoff at 95%), and spill buckets.

Piping Systems (IFC 5703.6)

Piping for flammable and combustible liquids must withstand operating pressures and prevent leaks:

• Materials: Piping must be steel, iron, or other approved materials. Nonmetallic piping is generally restricted to underground installations.
• Testing: Before service, piping must be hydrostatically tested to 150% of operating pressure, or pneumatically tested to 110%, but not less than 5 psi. The pressure must be held for 10 minutes.
• Protection: Underground piping must be protected against corrosion (using cathodic protection) and physical damage.

Dispensing Operations (IFC 5705.3)

Dispensing transfers liquids between containers, which increases vapor release and ignition risks:

• Dispensing Rooms: Class I and II liquids must be dispensed in dedicated rooms. These rooms require a 2-hour fire-resistance-rated enclosure if adjacent to other occupancies, or 1-hour if the area is under 150 sq ft. Continuous mechanical exhaust ventilation must be provided at a rate of at least 1 cfm/sq ft, with inlets located within 12 inches of the floor.
• Grounding and Bonding: To prevent static spark ignition during transfer of Class I liquids, the dispensing nozzle, piping, and receiving container must be electrically bonded and grounded.
• Electrical Classification: All electrical equipment in dispensing rooms must comply with NEC (NFPA 70) Class I, Division 1 or Division 2 requirements.