The Nature Of Flammable Liquids (Classification)

  • First of all, we must identify the liquids as in fact being considered flammable. The manufacturer/distributor must provide what is called a material safety data sheet (MSDS) for their liquid. There are different classifications of flammable liquids per the National Fire Protection Association (NFPA), but generally any liquid with a flash point of 100°F or less is flammable. Liquids with flash points of greater than 100°F are classified as combustible liquids. The flash point is an indicator of how easy a liquid will ignite and is defined as the lowest temperature at which liquid will generate enough vapor to flash, but not continue to burn. Flammable and combustible liquids are further broken down into classes, as depicted in the following charts:
  • Flammable and combustible liquids themselves do not burn. In simple terms- it is the mixture of their vapours and air that burns. At normal room temperatures, flammable liquids can give off enough vapour to form burnable mixtures with air.
  • The vast majority of flammable liquids produce vapors that are heavier than air. This means that vapor that is released from containers (and no container contains all vapor) will sink to the floor and not travel very far without strong pressure. Vapor is released through expansion/contraction of the containers. Most containers are designed to relieve pressure build-up that occurs during movement, temperature fluctuations, and other factors.
  • Because flammable liquids (and to a lesser extent- combustible liquids) ignite much easier and burn much faster/hotter than typical combustible material, special care must be given to separating these materials from potential ignition sources. Ignition sources that are not normally a concern with ordinary combustible materials become significant when flammable liquids are present. These include static electricity, electrical systems (even enclosed with metal conduit), heating units, hot surfaces, motors, and even simply heat itself. It is called spontaneous combustion when this occurs. Related to the flashpoint is a material’s autoignition temperature- the temperature at which the material self-ignites without the aid of an external ignition source.
  • The specific gravity of a liquid is important to know. Specific gravity is defined as the ratio of the weight of a substance (the liquid) to the weight of water and is noted as the base at which other liquids are based on. The specific gravity of a liquid indicates whether or not that liquid will float on top of water or whether water will float on top of the liquid. This is important from a fire protection standpoint when water (which is typically what a fire department will use to fight fire) is applied to burning liquids. This is why drainage or containment of the liquids is a critical consideration when storing any quantity.
  • Water miscibility: This is a measure of whether the liquid that mixes in all proportions with water (generally only includes alcohols and acetone).
  • Viscosity: This is defined as the resistance of a liquid to flow freely. If the liquid is thick enough, it will not form a pool. One of the items that make flammable liquids so dangerous is a flowing pool spreading the fire.  If the liquid will not form a pool, it easier to control as it will tend to “stay put” easier. There are various means to measure viscosity. For this article, we won’t go into the scientific methods that are used, however, the more viscous the liquid is- generally the lesser protection it requires, and thus viscous liquids can often be treated as standard commodities (1, 2, 3, 4, plastics) and may not need containment or drainage.

Flammable Chart 1

Regulatory & Best Practice Requirements Governing The Use And Storage Of Flammable Liquids

  • National Fire Protection Association (NFPA): NFPA 30 Flammable and Combustible Liquids Code, 2012 Edition is the primary standard that provides guidelines for the storage of flammable and combustible liquids. The NFPA, founded in 1896, is a consensus code publisher, meaning that codes are developed and voted on by stakeholders from a variety of industries/interests. NFPA 30, like all NFPA codes, is revised on a scheduled basis (generally every three years). Other NFPA codes that are related include:
    • NFPA 33: Standard for Spray Application Using Flammable or Combustible Materials, 2011 Edition
    • NFPA 34: Standard for Dipping, Coating and Printing Processes Using Flammable or Combustible Liquids, 2011 Edition
    • NFPA 56PS: Standard for Fire and Explosion Prevention During Cleaning and Purging of Flammable Gas Piping Systems, 2012 Edition
    • NFPA 329: Recommended Practice for Handling Releases of Flammable and Combustible Liquids and Gases, 2010 Edition
    • NFPA 385: Standard for Tank Vehicles for Flammable and Combustible Liquids, 2007 Edition
    • NFPA 497: Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas, 2008 Edition Flammable Chart 2
  • Occupational Safety & Health Administration (OSHA): OSHA is a governmental administration and division of the Department of Labor (DOL). As such, it is charged with the development of legal, enforceable standards to protect employees in the workplace. This goal requires OSHA to consider a variety of sources. OSHA considers NFPA as a primary source of best practice standards as relates to fire and life safety (though not the only source). OSHA and NFPA rarely conflict with each other, but in some instances OSHA includes compliance alternatives in which facilities can choose to comply with either OSHA’s specific regulatory language or NFPA requirements (e.g. means of egress in NFPA 101 Life Safety Code). OSHA also may add requirements specifically to protect employees or building occupants that NFPA may loosely recommend. The bottom line is that OSHA, being legally enforceable at all time, supersedes NFPA.
  • FM Global (formerly known as Factory Mutual, Inc.): FM Global is a private property insurance company founded in 1835. Along with adopting other standards (such as NFPA), they also conduct/fund their own research (including scientific testing laboratories) and publish risk management standards that address specific loss exposures. With regard to flammable liquids, FM Global diverts somewhat with regard to fire protection. As a general rule of thumb, FM Global Data Sheets are more conservative and offer specific narrow solutions.  Flammable Chart 3

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