Chapter 2 — Understanding How Matter Behaves

Changes of State

• A change of state or phase involves a change in the physical form of a substance, such as solid to liquid or liquid to gas.
• These changes always involve a change in heat.
• Matter contracts when it gets cold and expands when it gets hot, but water expands when it freezes.
• The temperature at which a solid turns into a liquid is called its melting point.
• The freezing point is the temperature at which a liquid solidifies or crystallizes.
• The boiling point is the temperature at which the vapor pressure of a liquid equals the atmospheric pressure.
• Evaporation is a surface phenomenon where molecules near the liquid's edge escape into the atmosphere as vapor.
• The rate of evaporation is affected by temperature, with higher temperatures resulting in faster evaporation.
• Sublimation is the transformation of a solid directly into a vapor without becoming a liquid.
• Dry ice (solid carbon dioxide) sublimates, as does iodine, which can travel through the air until it condenses in a cool spot.

Critical Points

• Critical points are thresholds in temperature and pressure that can initiate chemical reactions that cannot be stopped until completion.
• The critical temperature is the minimum temperature above which a gas cannot be liquefied, regardless of pressure.
• The critical pressure is the pressure needed to liquefy a gas at its critical temperature.
• The autoignition temperature is the lowest temperature at which a substance will ignite without an ignition source.
• The self-accelerating decomposition temperature (SADT) is the temperature above which decomposition continues unimpeded, regardless of external temperature.
• The maximum safe storage temperature (MSST) is the maximum safe temperature for storage, well below the substance's SADT.
• Polymerization is a chemical reaction where monomers combine to form polymers.

Temperature & Pressure

• As temperature increases, so does pressure.
• The speed of molecules increases with temperature, increasing the force on the container walls, leading to higher pressure.

Understanding Properties

• Understanding physical properties helps hazmat technicians identify the hazards of a substance.
• A low boiling point generally indicates a low flash point, leading to a high vapor pressure.
• A high boiling point and flash point typically indicate a low vapor pressure.
• SDSs provide information on a material's appearance, including color. However, color may not always be a reliable indicator of purity.

Temperature Measurement

• Common temperature scales include Celsius (°C) and Fahrenheit (°F).
• Kelvin (K) and Rankine (°Ra) are also used in scientific contexts.
• Increasing heat increases the movement of molecules within an object.

Flash Point

• The flash point is the lowest temperature at which a liquid can form an ignitable mixture in air near the liquid's surface but won't sustain continuous burning.
• NFPA defines flammable liquids as having flash points below 100°F (38°C) and combustible liquids as having flash points above 100°F (38°C).
• US DOT defines flammable liquids as having flash points below 141°F (60°C).
• A lower flash point indicates higher flammability.
• Liquids themselves don't burn; the vapors produced from them do.
• The lower the molecular weight of a product, generally the lower its flash point.
• Vapors from liquids are typically heavier than air.

Viscosity

• Viscosity measures the internal friction of a liquid at a given temperature.
• It determines how easily a product flows.
• Liquids typically become thinner (more fluid) as they get hotter and thicker (less fluid) as they get colder.

Odor

• Odor is a characteristic scent produced by a chemical.
• Some chemicals have little or no odor, while others have strong, distinctive odors.
• A sudden or unexpected odor can indicate a chemical release.
• Odor reports from callers or victims can provide initial information, but never rely on odor alone to determine safety.

Appearance

• Materials have characteristic appearances based on their composition.
• Vapors from liquids or gases can displace oxygen, causing asphyxiation.
• Cryogenic liquids can cause frostbite and can make metals brittle.
• Rapid expansion of liquefied gases or cryogenic liquids can lead to high pressure and equipment failure (BLEVE).
• Gases may generate static electricity when released, potentially igniting flammable atmospheres.
• Cryogenic liquids and gases have reactive hazards different from their ambient temperature counterparts.

Water Reactions

• Anhydrous means "dry" or without water.
• Materials can be hydrophobic (water-repelling) or hydrophilic (water-absorbing).

Other Physical Properties

• Density is the mass of a substance per unit volume.
• Density generally decreases with increasing temperature.
• Density determines if something will sink or float in a liquid.
• Specific gravity compares the density of a substance to the density of water.
• Vapor density compares the density of a substance's vapor to air.
• Viscosity measures the resistance to flow.
• Odor is the smell produced by a substance.
• Appearance includes physical characteristics like color, state, and form.

Physical Properties

• An SDS will normally include a description of a substance's appearance, such as its physical state and color.
• The color listed on the SDS often represents an average value, as the actual color can vary depending on the specific batch shipped.
• Significant differences in color can indicate contamination or impurities, which may pose their own hazards.
• Temperature can influence the physical properties of a substance.
• Common temperature scales include Celsius (°C) and Fahrenheit (°F).
• The movement of molecules within a substance increases with heat.

Flammability and Flash Point

• Flammable liquids have a flash point, which is the minimum temperature required for the substance to form an ignitable mixture with air.
• NFPA defines flammable liquids as having a flash point below 100°F (38°C), while combustible liquids have a flash point above 100°F (38°C).
• U.S. DOT classifies flammable liquids as those with a flash point below 141°F (60°C).
• A lower flash point indicates higher flammability.
• The vapors produced by liquids actually burn, not the liquids themselves.
• Molecular weight is a significant factor affecting the flash point: lower molecular weight generally correlates with a lower flash point.
• Vapors from liquid products are often heavier than air.

State Changes and Cryogenic Liquids

• Matter can transition between solid, liquid, and gas states.
• Vaporization of liquids or gas release from pressurized cylinders can displace oxygen, leading to asphyxiation.
• Exposure to cryogenic liquids can cause severe frostbite, tissue damage, and embrittlement of metals.
• Rapid expansion of cryogenic liquids or liquified gases can generate high pressure and cause violent container failure (similar to a BLEVE).
• Some pressurized gases can create large static-electric charges during release, posing a risk of igniting flammable atmospheres.
• Cryogenic liquids can possess unique reactive hazards beyond those associated with the same substances at ambient temperatures.
• Liquid oxygen can form a sensitive contact explosive with asphalt, potentially detonated by a footstep.
• Liquid chlorine reacts violently with most organic materials, creating extreme fire danger in the event of a spill.

Water Reactions

• "Anhydrous" denotes a material without water.
• Hydrophobic elements repel water, while hydrophilic elements and materials absorb water.

Physical Properties and Measurements

• Density measures a substance's weight per unit volume.
• Density changes with temperature, becoming denser with colder temperatures.
• Comparing densities helps determine if an object will sink or float in a liquid.
• Density units include grams per milliliter (g/ml) or pounds per gallon (lb/gal).
• Specific gravity is a ratio of a substance's density to the density of water (which has a specific gravity of 1).
• Materials with a specific gravity less than 1 float in water, while those greater than 1 sink.
• Vapor density compares the density of a gas or vapor to air (density of 1).
• Gases with a vapor density less than 1 are lighter than air and will rise, while those greater than 1 are heavier than air and will sink.
• It's possible to estimate vapor density by dividing the molecular weight of a substance by the average molecular weight of air (29).
• Viscosity measures a liquid's internal friction at a specific temperature.
• Higher viscosity indicates thicker and less fluid substances.
• Odor is subjective and can alert responders to potential releases.
• Always use detection and monitoring equipment to assess atmosphere safety, never rely solely on odor.

Appearance

• Elements, compounds, and mixtures have a characteristic appearance based on their composition.
• An SDS will usually include a description of a material's appearance.

Matter and Its States

• Chemical composition remains constant during changes in state.
• Changes in state require heat transfer: heat is added during melting and boiling, and heat is removed during freezing and condensation.

Temperature and Its Impact

• Materials generally contract when cold and expand when hot, but exceptions occur (e.g., water expanding when freezing).
• Melting point is the critical temperature at which a solid turns into a liquid.
• Freezing point is similar to or the same as the melting point, but some materials can supercool.
• Boiling point is the temperature at which a liquid's vapor pressure equals atmospheric pressure.
• Evaporation is a surface phenomenon where molecules escape into the atmosphere as vapor.
• Evaporation rates are influenced by temperature: higher temperatures lead to faster evaporation.

Sublimation

• Sublimation is the direct conversion of a solid to a vapor without a liquid phase.
• Examples include dry ice (solid carbon dioxide) and iodine.
• Sublimation can lead to the movement of hazardous materials due to the condensation of vapors in cooler areas.

Critical Points

• Critical points are thresholds beyond which chemical reactions cannot be stopped until completion.
• Critical temperature is the minimum temperature above which a gas cannot be liquefied, regardless of pressure.
• Critical pressure is the pressure required to liquefy a gas at its critical temperature.
• Autoignition temperature is the lowest temperature at which a substance ignites in air without an external ignition source.
• Self-accelerating decomposition temperature (SADT) is the temperature at which an unstable substance decomposes uncontrollably.
• Maximum safe storage temperature (MSST) is the maximum temperature for safe storage, lower than the SADT
• Polymerization is a chemical reaction where monomers combine to form larger polymer molecules.

Temperature and Pressure

• Temperature and pressure are directly proportional: Increased temperature results in increased molecular speed and higher pressure.

Physical Properties

• Knowledge of physical properties aids hazmat technicians in understanding the product involved in an incident.
• Materials with low boiling points typically have low flash points and high vapor pressure and content.
• Materials with high boiling points and flash points generally have low vapor pressure and content.

States of Matter

• Solids:
  • Have a fixed volume and shape.
  • Can become airborne in a fine, powdered form.
• Liquids:
  • Have a fixed volume but take the shape of their container.
  • Molecules can flow freely.
  • May be more difficult to contain than solids due to their mobility and potential for vaporization.
• Gases:
  • Have no fixed volume or shape and will expand to fill any container.
  • Molecules possess high energy and mobility.
  • Are the least dense state of matter and are compressible.
  • Cooling can cause gases to condense into liquids.
  • Pose the greatest risk to emergency responders due to their volatility and the potential for inhalation exposure.
  • May have a variety of hazards including toxicity, corrosivity, flammability, high pressure, extreme cold and large expansion ratios.

Atmospheric Pressure

• Atmospheres (atm) are commonly used as a unit of pressure in the US.
• Vaporizing liquids or gases released from pressurized cylinders can displace oxygen, leading to asphyxiation.

Cryogenic Liquids and Gases

• Cryogenics can cause extreme cold, leading to:
  • Frostbite and tissue damage.
  • Brittleness of metals, resulting in container or structural failure.
  • Rapid expansion with high pressure buildup, potentially causing a BLEVE (Boiling Liquid Expanding Vapor Explosion).
  • Static electric charges upon release, posing an ignition risk for flammable atmospheres.
  • Unique reaction hazards, such as the violent reaction between liquid oxygen and asphalt or liquid chlorine with organic materials.

Water Reactions

• Anhydrous implies "dry" or without water.
• Hydrophobic materials repel water.
• Hydrophilic materials absorb water.

Additional Physical Properties

• Density: A measure of mass per unit volume.
  • Densities change with temperature: colder matter is denser.
  • Helps determine if a substance will float or sink in a liquid.
  • Usually expressed in grams per milliliter (g/ml) or pounds per gallon (lb/gal).
• Specific Gravity: The ratio of a substance's density to the density of water.
  • Water has a specific gravity of 1.
  • Substances with specific gravity less than 1 float on water, while substances with specific gravity greater than 1 sink.
• Vapor Density: The ratio of a gas or vapor's density to the density of air (air = 1).
  • Gases with a vapor density less than 1 are lighter than air and will rise.
  • Gases with a vapor density greater than 1 are heavier than air and will sink.
  • Similar to the Compressed Gas Association (CGA) specific gravity and NIOSH RgasD (relative gas density) measurements.
• Viscosity: A liquid's resistance to flow.
• Odor: The smell of a substance.
• Appearance: The visual characteristics of a substance.