Section 3.3: Storage, Use, and Handling General Requirements

Storage, Use, and Handling General Requirements (IFC Chapters 50-67)

Regardless of whether hazardous materials are stored in quantities below the Maximum Allowable Quantity (MAQ) within a control area or in a Group H occupancy, they are subject to the general safety requirements of IFC Chapters 50 through 67. These requirements focus on passive and active mitigation measures to prevent chemical releases and to contain hazards if a release occurs. For a plans examiner, verifying these details on architectural, mechanical, plumbing, and electrical drawings is essential to ensure that the facility is designed to survive a containment failure without catastrophic consequences.

Mechanical Ventilation (IFC Section 5004.3)

Indoor storage and use areas for hazardous materials must be provided with mechanical exhaust ventilation. The ventilation system must be designed to run continuously, or it must be designed to start automatically when a gas detection system detects vapors or gases at a concentration of 25 percent of the Lower Flammable Limit (LFL) or LEL, or at the Permissible Exposure Limit (PEL) for toxic materials.

Continuous Mechanical Exhaust Rate

The mechanical exhaust ventilation system must provide a minimum exhaust rate of not less than 1 cubic foot minute per square foot ($1\text{ cfm/ft}^2$) of floor area over the storage or use area. This continuous flow prevents the accumulation of flammable or toxic vapors under normal conditions.

Inlet and Duct Design

The elevation of the exhaust duct inlets is determined by the vapor density of the hazardous materials:

• Heavy Vapors (Vapor Density > 1): Vapors that are heavier than air (such as gasoline, propane, and acetone) will sink and accumulate at the floor level. The plans examiner must verify that the exhaust inlets are located within 12 inches of the floor to capture these heavy vapors.
• Light Vapors (Vapor Density < 1): Vapors that are lighter than air (such as hydrogen and methane) will rise. The exhaust inlets must be located near the ceiling or high points of the room.

Ducts must be constructed of approved noncombustible materials. If corrosive vapors are present, the ducts must be constructed of corrosion-resistant materials or coated with a compatible lining. The discharged air must be directed to an approved outdoor location, situated at least 10 feet from property lines, openings into buildings, and fresh air intakes to prevent re-entrainment of hazardous vapors.

Secondary Containment (IFC Section 5004.2)

Secondary containment is a physical barrier designed to capture and hold spills of liquid or solid hazardous materials, preventing them from spreading, reacting with other chemicals, or entering the public sewer system.

When Secondary Containment is Required

Under IFC Section 5004.2, secondary containment is required for liquid and solid hazardous materials in storage or use when:

• The capacity of an individual storage vessel exceeds 55 gallons.
• The aggregate capacity of multiple vessels in a room or area exceeds 1,000 gallons.

Sizing Sump Capacity

The secondary containment system must be sized to contain a spill from the largest vessel, or 10 percent of the aggregate capacity of all vessels in the containment area, whichever is greater. If the storage area is protected by an automatic sprinkler system, the plans examiner must calculate and add the volume of water generated by the sprinkler system operating for a design duration of 20 minutes: $\text{Containment Volume} = \max(\text{Volume of Largest Vessel}, 0.10 \times \text{Aggregate Volume}) + \text{Sprinkler Water Volume}$

The sprinkler water volume is calculated based on the sprinkler system design density (e.g., $0.2\text{ gpm/ft}^2$ over the design area, typically the entire room) multiplied by 20 minutes: $\text{Sprinkler Water Volume (gallons)} = \text{Design Density (gpm/ft}^2) \times \text{Design Area (ft}^2) \times 20 \text{ minutes}$

The containment basin must be liquid-tight, constructed of materials compatible with the stored chemicals, and provided with an approved method of draining or pumping out accumulated liquids.

Separation of Incompatible Materials (IFC Section 5003.9.8)

Incompatible materials are substances that, when mixed, can react violently, generate toxic gases, or cause a fire. Examples include acids and bases, oxidizers and flammable liquids, and water-reactive chemicals and water-based solutions. The IFC mandates that incompatible materials in storage or use must be separated to prevent accidental mixing. The plans examiner must verify that the construction documents indicate one of the three permitted separation methods:

1. Distance: A minimum horizontal separation of not less than 20 feet.
2. Noncombustible Barrier: A noncombustible partition extending not less than 18 inches above and to both sides of the stored materials. This barrier must have a fire-resistance rating of not less than 1 hour.
3. Safety Cabinets: Storing one or both classes of incompatible materials inside approved hazardous materials cabinets.

Electrical Classification (IFC Section 5003.9.4 & NFPA 70)

Areas where flammable gases, vapors, or dusts are present must have electrical installations that comply with NFPA 70 (National Electrical Code) Article 500. The plans examiner must review the electrical drawings to ensure that the boundary of the classified area is correctly indicated:

• Class I: Locations where flammable gases or vapors are or may be present.
• Class II: Locations where combustible dusts are or may be present.
• Class III: Locations where easily ignitable fibers are present.
• Division 1: Hazard is present under normal operating conditions.
• Division 2: Hazard is present only under abnormal conditions (such as a container leak or equipment failure).

All electrical equipment, including light fixtures, switches, motors, and wiring methods, must be listed for the specific Class, Division, and Group of the hazard. In Class I, Division 1 locations, electrical devices must be explosion-proof or intrinsically safe to prevent any electrical spark or hot surface from igniting the surrounding atmosphere.