Flammable Materials PDF

Flammable Materials A flammable substance is a solid, liquid, vapor, or gaseous material that ignites easily and burns, or combusts, rapidly when exposed to an ignition source. A combustible substance is one that is more difficult to ignite, but still burns rapidly when exposed to an ignition sourc...

Flammable Materials A flammable substance is a solid, liquid, vapor, or gaseous material that ignites easily and burns, or combusts, rapidly when exposed to an ignition source. A combustible substance is one that is more difficult to ignite, but still burns rapidly when exposed to an ignition source. For combustion, or fire, to occur, there are four components that must come together at the same time and in the right proportions. In the past, it was thought that three components were needed for fire - fuel, oxygen, and heat -- and these were depicted as a *fire triangle*. Today, the fire triangle concept has been expanded into what is called the *fire tetrahedron*, where the four components are each represented by a side of the tetrahedron.  The fourth component is an ignition or some sort of chemical reaction which starts the fire process and perpetuates combustion once it has started. Once a fire starts, the chain reaction sustains it by continuously generating heat, which, in turn, keeps the fuel burning and the combustion process going. By disrupting any of these elements, a fire can be prevented or extinguished. This knowledge helps in selecting appropriate suppression agents and strategies: - Removing fuel: Eliminating combustible materials (e.g., shutting off gas lines or removing flammable items) starves the fire. - Reducing heat: Water or cooling agents lower the temperature below the ignition point. - Limiting oxygen: Smothering with foam, CO₂, or blankets prevents oxygen from feeding the fire. PFAS (per- and polyfluoroalkyl substances) work with fire by acting as a surfactant in firefighting foams, creating a thin film that effectively smothers flames by cutting off oxygen access to the fuel, essentially \"blanketing\" the fire and preventing it from reigniting. - Interrupting the chemical reaction: Specialized agents like dry chemical powders or halons disrupt the chemical chain reaction sustaining combustion. Combustion is a chain reaction that is both initiated and sustained by free radicals. As with fuel, oxygen, and heat, if you remove the free radicals, the chain reaction is interrupted---the fire extinguished. This is the mechanism by which halon fire-extinguishing agents work. Halons contain four to six chlorine, fluorine, bromine, and/or iodine atoms. They react with and remove, or scavenge, free radicals from the combustion process and extinguish the fire. The ease in which halons react with free radicals is how they damage the Earth's ozone layer, as well as why they have been replaced by more ozone-friendly materials. The *flash point* of a substance is a good indicator of how easily the material can be ignited. The flash point is the minimum temperature at which a liquid gives off vapor in sufficient concentration to form an ignitable mixture with air near the surface of the liquid. Two tests can be used to determine a flash point: the open-cup and closed-cup methods. Most regulatory definitions of flammability and combustibility are based on closed-cup flash point measurements. Whether a material is classified as flammable depends upon the regulatory framework and in some cases, each country's regulations. The specific properties that define and distinguish between flammables and combustibles vary among the organizations, agencies, and regulations focused on fire safety. **Flammable Liquids** The Occupational Safety and Health Administration (OSHA) places flammable liquids into four categories: **Table B.6.1 from 29 CFR 1910.1200: Criteria for flammable liquids** **Category** **Criteria** -------------- ----------------------------------------------------------------------- 1 Flash point \< 23°C (73.4°F) and initial boiling point ≤ 35°C (95°F) 2 Flash point \< 23°C (73.4°F) and initial boiling point \> 35°C (95°F) 3 Flash point ≥ 23°C (73.4°F) and ≤ 60°C (140°F) 4 Flash point \> 60°C (140°F) and ≤ 93°C (199.4°F) In the United Nation's Globally Harmonized System (GHS) of Classification and Labelling of Chemicals, the more hazardous a material, the lower the category number. Thus, a Category 1 flammable liquid is more hazardous than the Category 4 material. This is opposite to other current systems, such as NFPA 704: Standard System for the Identification of the Hazards of Materials for Emergency Response or the Hazardous Materials Information System (HMIS)---both use a Category 1 as lower hazard than a Category 4. Under the GHS revisions adopted in 2012, OSHA removed the term *combustible* liquids, but other regulatory agencies may still sue the term. The NFPA 30: Flammable and Combustible Liquids Code provides definitions for flammable and combustible liquids based on their flash points and boiling points. Flammable liquids are those that have a flash point below 100°F (37.8°C). They are further divided into classes based on their boiling points: - Class IA: Flash point below 73°F (22.8°C) and boiling point below 100°F (37.8°C). - Class IB: Flash point below 73°F (22.8°C) and boiling point at or above 100°F (37.8°C). - Class IC: Flash point at or above 73°F (22.8°C) but below 100°F (37.8°C). Combustible liquids are those with a flash point at or above 100°F (37.8°C). They are divided into the following classes: - Class II: Flash point at or above 100°F (37.8°C) and below 140°F (60°C). - Class IIIA: Flash point at or above 140°F (60°C) and below 200°F (93°C). - Class IIIB: Flash point at or above 200°F (93°C). For shipping, the US Department of Transportation (DOT) classifies a flammable liquid (DOT Class 3) as a liquid having a flash point of not more than 60 °C (140 °F), or any material in a liquid phase with a flash point at or above 37.8 °C (100 °F). Under DOT, a combustible liquid is any liquid that does not meet the definition of any other DOT hazard class and has a flash point above 60 °C (140 °F) and below 93 °C (200 °F). With the exception of some special cases, the Department of Transportation (DOT) regulates materials with flash points of no more than 140°F as flammable and above 140°F but below 200°F as combustible. The Environmental Protection Agency uses the term *ignitable* in the Resource Conservation and Recovery Act (RCRA) regulations found in 40 *CFR* § 261.21. A solid is ignitable if it "is capable, under standard temperature and pressure, of causing fire through friction, absorption of moisture or spontaneous chemical changes and, when ignited, burns so vigorously and persistently that it creates a hazard." A flash point less than or equal to 60°C/140°F is the criterion established by the Environmental Protection Agency (EPA) to determine whether a waste is hazardous by virtue of its ignitability. The EPA has several other definitions for the word *flammable*, depending on the specific regulation being dealt with. For example, for refrigerants, EPA defers to ASHRAE Standard 34, *Designation and Safety Classification of Refrigerants*, to define whether a refrigerant is flammable or not. For pesticides, extremely flammable, flammable, and combustible classifications are defined in 40 CFR 156.78. Therefore, it is important to review the definition section of each specific regulation. **Flammable Solids** OSHA defines a *flammable solid* as "a solid which is a readily combustible solid or which may cause or contribute to fire through friction." *Readily combustible solids* are "powdered, granular, or pasty chemicals which are dangerous if they can be easily ignited by brief contact with an ignition source, such as a burning match, and if the flame spreads rapidly." Under DOT, flammable solids are a Class 4 hazard, and the complete definition can be found at 49 *CFR* § 173.124. NFPA 400, *Hazardous Materials Code*, defines a flammable solid as "a solid substance that is liable to cause fire resulting from friction or retained heat from manufacture, that has an ignition temperature below 212°F (100°C), or that burns so vigorously or persistently when ignited that it creates a serious hazard." **Flammable Gases** OSHA defines *flammable gas* as a gas having a flammable range with air at 20°C (68°F) and a standard pressure of 101.3 kPa (14.7 psi). DOT defines a flammable gas as any material that is a gas at 20 °C (68 °F) or less and 101.3 kPa (14.7 psia) of pressure that is also ignitable at 101.3 kPa (14.7 psia) when in a mixture of 13 percent or less by volume with air, or has a flammable range at 101.3 kPa (14.7 psia) with air of at least 12 percent regardless of the lower limit. **Pyrophoric Materials or Spontaneously Combustible Materials** OSHA defines pyrophoric material as "a liquid or solid, which even in small quantities, is liable to ignite within five minutes after coming into contact with air." DOT defines pyrophoric material as "a liquid or solid that, even in small quantities and without an external ignition source, can ignite within five (5) minutes after coming in contact with air." DOT also defines a *self-heating material* as a material that generates heat through a reaction of that substance with oxygen (in air) that may lead to self-ignition and combustion. Many common materials in this classification will tend to oxidize when wet or damp, and oxidation generates heat. If enough heat is generated, ignition occurs. There are oxidizing oils, such as linseed or tung oil, that will oxidize when added to cloth, as in refinishing wood and rubbing the oils onto the surface, and if conditions are right, they will begin to self-heat. Examples of pyrophoric materials include the alkali metals (lithium, sodium, potassium, rubidium, and cesium), finely divided powdered metals (aluminum or magnesium). **Lower and Upper Flammability Limits** One of the most important measurable characteristics of flammable and combustible materials is the range of fuel/air mixtures that will burn when ignited. The upper flammability limit (UFL) and lower flammability limit (LFL) define the concentration range of a flammable gas or vapor in air where combustion can occur. The LFL is the lowest concentration of the substance in air that can ignite, while the UFL is the highest concentration that can sustain combustion. Outside of this range, the mixture is either too lean (below LFL) or too rich (above UFL) to ignite. Understanding these limits is crucial in fire safety because it helps assess the risk of fire or explosion in various environments. For example, monitoring vapor concentrations in confined spaces ensures they remain outside the flammable range, reducing the likelihood of ignition. Additionally, knowing the flammability limits aids in designing ventilation systems, establishing safe operating procedures, and developing emergency response plans to prevent hazardous situations. **Other Terms of Importance** *Vapor pressure* is the pressure exerted by a vapor in equilibrium with its liquid or solid phase at a given temperature. It reflects a substance\'s volatility. Materials with high vapor pressure (e.g., gasoline) readily produce vapors at lower temperatures, increasing the risk of ignition. High vapor pressure can lead to the accumulation of flammable vapors in confined spaces, creating an explosive environment. *Vapor density* is the weight of a vapor compared to the weight of an equal volume of air (where air has a vapor density of 1).Vapors with a density greater than 1 (e.g., propane, with a vapor density of \~1.5) tend to settle near the ground, where they can accumulate and spread to distant ignition sources. *Specific gravity* is the ratio of a liquid\'s density compared to water (where water has a specific gravity of 1). Liquids with a specific gravity less than 1 (e.g., gasoline at \~0.7) float on water, making it difficult to extinguish fuel fires with water alone. Knowledge of specific gravity informs strategies for spill containment and fire suppression. For instance, foam is often used to create a barrier on the surface of lighter-than-water flammable liquids. *Autoignition temperature* is the minimum temperature at which a substance ignites spontaneously without an external ignition source. Substances with low autoignition temperatures (e.g., diethyl ether, \~160°C/320°F) pose higher fire risks under high-temperature conditions. Equipment and storage areas must be designed to prevent exposure to temperatures near or above the autoignition temperature of stored flammable materials.