Is its vapor dangerous?

Key Points

  • Two kinds of vaporThe gas given off by a substance that is liquid (or solid) at normal temperatures and pressures. can be dangerous: (1) flammableEasy to ignite and burns readily. vapor, which can burn or explode, and (2) toxicPoisonous; can injure or kill people or other organisms. vapor, which can poison people who breathe it. The vapor from a flammable liquid can be hazardous if its concentrationThe amount of a chemical present in a given weight or volume of air. Concentration of a gas in air may be expressed in units such as parts per million (by volume) or milligrams per cubic meter. in air reaches the flammable rangeRange of concentration (of a gas in air) between the Lower and Upper Explosive Limits (LEL and UEL). Gas in the flammable range will burn rapidly or explode when ignited, because it has been premixed to the right mixture of fuel and air for burning to occur. If the concentration falls below the LEL, then there isn't enough fuel in the air to sustain a fire or an explosion--it is too lean. If the concentration rises above the UEL, then there isn't enough oxygen to sustain a fire or an explosion--it is too rich (much like an engine that can't start because it has been flooded with gasoline). (higher than the LELLower explosive limit or lower flammability limit. Lowest concentration of a flammable vapor in air at which explosion or combustion can occur. and lower than the UELUpper explosive limit or upper flammability limit. Highest concentration of a flammable vapor in air at which explosion or combustion can occur.). The vapor from a toxic liquid can be hazardous if its concentration reaches a dangerously high level AND people are exposed to it for a dangerously long time.
  • You can obtain a "ballpark" estimate of the area that might be affected by an evaporating vapor from the Emergency Response Guidebook (ERG). For a more detailed, scenario-specific estimate, run ALOHA.
  • Vapor concentrations will be higher鈥攁nd more likely to be hazardous鈥攚hen the liquid is more volatileEvaporates readily., the temperature is higher, and/or the pool of spilled liquid is larger in area.
  • Vapor pressureA measure of a substance's tendency to evaporate; liquids with higher vapor pressures evaporate faster. is a measure of a liquid's volatilityReadiness to evaporate. The volatility of a given substance increases with temperature.. Generally, the higher the vapor pressure, the greater the volatility, and the more likely that dangerously high vapor concentrations could be produced. You can find a substance's vapor pressure in CAMEO 365bet娱乐.
  • Confinement can increase the concentration of a vapor, whether the confinement is partial (between ships or buildings, underneath piers, in stairwells) or complete (in a vessel hold or storage tank).
  • How much vapor evaporates from a liquid spilled into water depends on many factors; you should try to contact an expert for assistance with spills on water.

Backgrounder

An evaporating vapor can be hazardous if its concentration in air reaches a dangerously high level. A vapor's concentration can be measured with portable detectors or predicted with computer models like ALOHA. If a measured or predicted concentration exceeds an established Level of Concern (LOC) for the chemical, a hazard is expected to exist.

Three kinds of vapors can be hazardous:

  • Toxic vaporToxic vapor

    An evaporating toxicPoisonous; can injure or kill people or other organisms. vaporThe gas given off by a substance that is liquid (or solid) at normal temperatures and pressures. can be hazardous if its concentrationThe amount of a chemical present in a given weight or volume of air. Concentration of a gas in air may be expressed in units such as parts per million (by volume) or milligrams per cubic meter. becomes high enough to poison people who breathe it. Exposure duration is important for toxic substances: people who breathe a toxic vapor for a longer time period are more likely to be harmed or to sustain worse injury.

    To use CAMEO 365bet娱乐 to find out whether a substance is toxic:

    1. Run a search for the substance, and then open its chemical datasheet.
    2. In the Chemical Identifiers section, look at the NFPANational Fire Protection Association (www.nfpa.org), a private, non-profit organization that produces technical data related to fire protection and prevention, including the widely used NFPA diamond that contains codes representing chemical hazards. 704 table and check the number in the blue (health hazard) quadrant in the NFPA diamond. If the number is between 1 and 4, the substance is toxic. The higher the number, the more toxic the substance.
    3. In the Hazards section, review the Health Hazard summary.
    4. In the Physical Properties section, look for Levels of Concern (LOCs) such as AEGLsAcute Exposure Guideline Levels are levels of concern representing the adverse health effects of a hazardous substance on members of the general public. AEGL values were developed by the National Advisory Committee on AEGLs. As of November 2011, ongoing AEGL development will be done by a National Academy of Sciences subcommittee (www.epa.gov/aegl)., ERPGsEmergency Response Planning Guidelines are levels of concern representing the adverse health effects of a hazardous substance on members of the general public. ERPGs are developed by the ERPG committee of the American Industrial Hygiene Association (www.aiha.org)., PACsProtective Action Criteria for 365bet娱乐. This dataset includes the three common public exposure guidelines (AEGLs, ERPGs, and TEELs). When a chemical has been defined under multiple guidelines, the PACs dataset uses a hierarchical system to present a single set of values for each chemical., and IDLHImmediately Dangerous to Life and Health limits, levels of concern for adult workers; estimate of the highest concentration in air from which escape is possible without permanent injury (if their respirators fail). IDLHs are established by the National Institute for Occupational Safety and Health (www.cdc.gov/niosh). values. The lower the LOC, the more hazardous the substance. Use an LOC to determine whether a measured or predicted vapor concentration might be high enough to harm people. If the vapor concentration exceeds the LOC, a hazard may exist.
  • Flammable vaporFlammable vapor

    An evaporating flammableEasy to ignite and burns readily. vaporThe gas given off by a substance that is liquid (or solid) at normal temperatures and pressures. can be hazardous if its concentrationThe amount of a chemical present in a given weight or volume of air. Concentration of a gas in air may be expressed in units such as parts per million (by volume) or milligrams per cubic meter. reaches the flammable rangeRange of concentration (of a gas in air) between the Lower and Upper Explosive Limits (LEL and UEL). Gas in the flammable range will burn rapidly or explode when ignited, because it has been premixed to the right mixture of fuel and air for burning to occur. If the concentration falls below the LEL, then there isn't enough fuel in the air to sustain a fire or an explosion--it is too lean. If the concentration rises above the UEL, then there isn't enough oxygen to sustain a fire or an explosion--it is too rich (much like an engine that can't start because it has been flooded with gasoline).. That range is between the Lower Explosive LimitAlso called lower flammability limit. Lowest concentration of a flammable vapor in air at which explosion or combustion can occur. (LEL) and the Upper Explosive LimitAlso called upper flammability limit. Highest concentration of a flammable vapor in air at which explosion or combustion can occur. (UEL).

    To use CAMEO 365bet娱乐 to find out whether a substance is flammable:

    1. Run a search for the substance, and then open its chemical datasheet.
    2. In the Chemical Identifiers section, look at the NFPANational Fire Protection Association (www.nfpa.org), a private, non-profit organization that produces technical data related to fire protection and prevention, including the widely used NFPA diamond that contains codes representing chemical hazards. 704 table and check the number in the red (flammabilityA substance's tendency to ignite or take flame. Flammability is closely related to the volatility of a substance (and is not its relative ability to burn in the presence of oxygen with the evolution of heat). hazard) quadrant in the NFPA diamond. If the number is between 1 and 4, the substance is flammable. The higher the number, the more flammable the substance.
    3. In the Hazards section, review the Fire Hazard summary.
    4. In the Physical Properties section, look for the LEL and the UEL. Together, they tell you the flammable range for the vapor in air.
  • Asphyxiation hazardsAsphyxiation hazards

    Vapors from nonflammableDifficult to ignite., non-toxic liquefied gases (such as nitrogen, carbon dioxide, and helium) can be asphyxiation hazards if the concentration becomes high enough to substantially displace oxygen from the air, lowering the concentration of oxygen in the air. The lower the oxygen concentration, the greater the hazard. The risk is higher in confined areas.

    The normal concentration of oxygen in the atmosphere is about 21%. When it drops below 17%, people breathing that air are considered at risk from oxygen deficiency. At about 16%, people find it hard to think and pay attention. Judgment is seriously impaired at about 12% oxygen. Below about 10%, people can lose consciousness, be unable to move, experience convulsions, or die. (Compressed Gas Association, Inc. 2001. Safety bulletin: Oxygen-deficient atmospheres.)

Vapor Pressure聽and Volatility

Image showing how volatility increases with vapor pressure. Above 760 mm Hg, the substances are gases. Below 1-10 mm Hg, the substances are nonvolatile liquids and solids. In between those values, the substances are volatile liquids.How much vapor evaporates from a pool of spilled liquid depends on the amount spilled and the liquid's volatility. The greater the liquid's volatility, the greater its tendency to evaporate, and the higher the vapor concentration is likely to rise.

Vapor pressure is the most common way to measure volatility. A liquid with a higher vapor pressure is more volatile, and evaporates vapor faster. More info on vapor pressureMore info on vapor pressure

Vapor pressureA measure of a substance's tendency to evaporate; liquids with higher vapor pressures evaporate faster. is the pressure an evaporating vaporThe gas given off by a substance that is liquid (or solid) at normal temperatures and pressures. exerts when it is in equilibrium with the liquid below it, at a given temperature. Vapor pressure is most often shown in units of millimeters of mercury (mm Hg), atmospheres (atm), or pounds per square inch (psi); 1 atm equals 760 mm Hg and 14.7 psi. Substances with vapor pressures higher than 760 mm Hg are gases.

A liquid's vapor pressure is influenced by its natural volatility and by the temperature. Higher temperatures increase vapor pressure, so that vapor evaporates faster from the liquid's surface.

You can find a substance's vapor pressure in CAMEO 365bet娱乐 by searching for a chemical, and then scrolling down to the Physical Properties section of the chemical datasheet.

Vapor Concentration

The concentration of vapor above an evaporating liquid is what can create a hazard, not the vapor pressure or evaporation rate. If the vapor concentration reaches a dangerous level, a hazard exists. On average, the concentration will be higher when (a) the vapor is evaporating faster and (b) the surface area of the spilled liquid is larger. More info on vapor concentrationMore info on vapor concentration

A vaporThe gas given off by a substance that is liquid (or solid) at normal temperatures and pressures. is more likely to reach a dangerously high concentrationThe amount of a chemical present in a given weight or volume of air. Concentration of a gas in air may be expressed in units such as parts per million (by volume) or milligrams per cubic meter. if it is confined in any way. For example, a vapor can be confined by being trapped between buildings in a city鈥攁nd vapors that are heavier than air can be confined in low areas (such as terrain depressions, stairwells, cargo holds, and storage tanks). Historical data suggest that a flammableEasy to ignite and burns readily. vapor cloud can explode only if it is at least partly confined.

In open areas, or when the wind is blowing strongly, a vapor is less likely to reach a dangerously high concentration.

Concentrations are usually patchy within the cloud of vapor above an evaporating liquid, with some patches higher in concentration than the average for the cloud.

Spills into聽Water

How much vapor might evaporate when a liquid spills into water depends on (a) whether the liquid sinks, floats, or is neutrally buoyant, (b) whether it is soluble or insoluble, and (c) whether the liquid is spilled all at once or more slowly. If possible, you should try to contact an expert for assistance with spills on water.

However, generally:

  • Evaporating vapor from a liquid that spills quickly into the water is more likely to reach higher concentrations than vapor from the same liquid spilled more slowly.
  • Insoluble liquids that are less dense than water will pool on the water surface and will evaporate vapor into the air.
  • Insoluble liquids that are much denser than water will pool on the bottom and will generate little or no vapor.