Incompatible Storage in a Metal-Finishing Room
At a metal-finishing shop, a 40 ft by 60 ft mixing room contains twelve 55-gallon drums of xylene and six 55-gallon drums of 68% nitric acid. All eighteen drums sit on a single uncurbed concrete floor; the nitric acid drums are nested between the xylene drums. A forklift punctures one xylene drum, releasing roughly 20 gallons onto the floor. The room has a gas-fired unit heater at floor level, a floor drain connected to the municipal sewer, and no automatic sprinklers. Two employees grab a 1½-inch water hose and prepare to wash the spill toward the drain. A supervisor stops them and calls you. The room's ventilation fan is off, and the outside temperature is 95°F. The shop also stores oily rags in an open bin near the heater. Identify the immediate chemical and fire hazards, the correct emergency actions, and the storage corrections needed.
1. What are the immediate fire and chemical hazards, and why is the employees' water-hose plan dangerous?
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Hazards. Xylene is a Class IB flammable liquid with a flash point near 77–81°F (25–27°C); its vapors are heavier than air and can reach the floor-level unit heater, the open rag bin, and the floor drain. Nitric acid at 68% is a strong oxidizer. If it contacts xylene, oily rags, or other organics, an exothermic oxidation reaction can generate heat, nitrogen oxides, and fire. Why water is dangerous: a water stream will spread the burning xylene, enlarge the pool, and carry acid into the sewer, where vapor ignition or a chemical reaction can occur. The correct first actions are to evacuate, sound the alarm, eliminate ignition sources, stop the release if safe, and call trained responders. Do not flush to the drain.
2. What extinguishing agent and tactical sequence should the responding team use?
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Agent choice. For the xylene pool, use alcohol-resistant foam or a dry chemical extinguisher; foam cools and blankets the surface, while dry chemical knocks down flame. Water fog may be used only by trained firefighters to cool exposures, never as a straight stream. Sequence: evacuate and establish an exclusion zone; wear SCBA and chemical-protective clothing; shut off the heater and ventilation; contain the spill with absorbent booms, keeping it out of the drain; cover the drain if safe. If the acid is involved, do not neutralize with a strong base in the spill area without control; contain separately. Monitor lower explosive limit and NOx. Withdraw if the acid container is heated or leaking.
3. What storage and housekeeping corrections are required?
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Storage corrections. Separate oxidizers from flammable liquids by a fire-rated wall or a minimum safe distance, and never nest acid drums among xylene. Provide curbing or a containment pallet sized for the largest container; the floor drain must be trapped, plugged, or eliminated from the chemical area. Bond and ground metal drums during dispensing. Remove the floor-level heater or replace it with a listed ignition-protected unit. Move oily rags into a self-closing metal can. Post NFPA 704 markings, label containers, train employees on incompatible-material separation, and keep a spill kit and appropriate extinguishers at the room entrance.