Preventing losses: Flammable and combustible liquids – Mixing Operations

The use of flammable and combustible liquids is common in the manufacturing processes of household items such as paints, cosmetics, personal care and cleaning products, as well as pharmaceuticals. Igniting easily, these liquids can cause severe fires and explosions resulting in catastrophic property damage and production downtime. In such scenarios, the potential loss of life is also very real.

It is vital to know which flammable and combustible liquids are on site so as to take the proper loss prevention and mitigation measures when mixing operations.

Flammable and combustible liquids – what's the difference?

Citation: NFPA 30 (Flammable and Combustible Liquids Code)

Fire and explosion hazards of flammable and combustible liquids

A common misconception is that the flammable liquid itself ignites to cause a fire and/or explosion. Actually, it is the vapor released from the liquid that ignites. In the case of an open container or when a leak occurs, these vapors can travel far from the source – along surveys, under doors or even across air ducts – and get ignited at a distance away from the source. If a sufficient amount of vapors accumulate within a confined space, it can cause an explosion if ignited.

Due to the fire and explosion hazards, the handling of flammable liquids used in industrial processes requires a high level of care. The same applies to combustible liquids when heated above their flash point. The term flammable liquid as referred to in this document also applies to combustible liquids heated above their flash point.

Loss prevention measures to avoid the risk of a potential fire or explosion

  • Eliminate and control potential ignition sources:
    • Classify all electrical equipment in process areas using flammable liquids to avoid the possibility that they act as a source of heat or ignition. This includes lighting fixtures, switches, power outlets, electric motors etc. Refer to the rating requirements of NFPA 30 for more information. 
    • To avoid the accumulation of static electricity generated in the handling and transfer of flammable liquids, all equipment should be reduced to the same electrical potential through bonding and grounding devices. Accumulation of static electricity can result in ignition or explosion of flammable vapors.
    • Ban smoking, avoid carrying out hot works, and use only spark resistant tools in any area where flammable and combustible liquids are present.
  • Ensure sufficient ventilation so vapors do not accumulate where flammable liquids are used. A well designed and maintained system can effectively remove vapors and significantly reduce the hazard of fire and explosion. Ensure regular cleaning of ducts and filters to reduce the likelihood of spontaneous combustion. Spot extraction points are necessary to remove vapors generated in process equipment such as mixing tanks, vessels or immersion containers. Exhaust ventilation discharge should be to a safe location outside of the building.
  • Ensure process equipment and vessels are built to prevent unintentional leakage of liquids and vapors or to minimize the amount released should a leak occur. In general, systems and processes containing flammable liquids should be designed so that liquids are kept as much as possible in fully enclosed systems. Equipment and piping should be built of materials compatible with the substances being used, and also resistant to fire and mechanical damage. Plastic or any combustible materials should be avoided.
  • Safety shutoff valves should be provided in piping systems to stop the flow of flammable liquids in the event of a fire or explosion. Consider installing valves on the discharge of tanks, bottom piping off large mixing tanks before any pump, at points where flammable liquids use and at the entrance point to a building or room where flammable liquids are used.
  • Maintain good housekeeping conditions, prohibiting any kind of storage and the accumulation of combustible material in production and processing areas that use flammable liquids.

Loss mitigation measures to control the escalation risk of a potential fire or explosion

  • Operations involving the use of flammable liquids should take place in non-combustible buildings, preferably in a dedicated location isolated from other areas. If a dedicated location is not feasible, a separate area for operations involving flammable liquids should be created through fire rated walls.
  • Fire sprinklers protection and water spray systems should be in place. Process areas should be equipped with automatic sprinklers or water spray systems designed in accordance with NFPA or equivalent standards. Should the facility not have access to water supply, operations should be conducted in a reinforced concrete building or protective structural steel supporting the building structure and equipment with fireproofing.
  • Buildings drainage systems are essential to direct flammable liquid spills or fires from a process area to a safe location and mitigate escalation. Drainage systems should be designed to handle the anticipated worst case release of material plus the water needed for firefighting.   

To ensure prevention and mitigation measures are adequately maintained when dealing with flammable liquids, proper management and emergency response programs, staff trainings and audits should be in place.

  • Follow manufacturer's guidelines regarding maintenance and testing procedures for process safety and protection systems and devices.
  • Implement a routine of periodic inspections to check the operating status of liquid transfer systems. Particular attention should be paid to hoses and connections for any signs of wear or leakage.
  • Elements of Process Safety Management (PSM) should be implemented to a fundamental level – even in the absence of regulatory requirements. Key programs include:
    • Management of change
    • Hazard analysis/review
    • Process safety information
    • Regular operator training
    • Incident investigation
  • Establish specific emergency procedures to address cases involving the release and ignition of flammable liquids. As a minimum this should include
    • Immediate notification to the fire department
    • Activation of plant emergency organization
    • Cut-off of flow of flammable liquids to processing area
    • Early identification of firefighting methods
    • Conducting annual drills to address all aspects of emergency response


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