Chemical and Physical Properties, Exposure Limits, and Routes of Exposure Practice Questions

25 multiple-choice questions on Chemical and physical properties, exposure limits, and routes of exposure for paramedic and EMT students, from Chapter 50 (Hazardous Materials). Read each question, pick your answer, then tap Show answer to check it and read the explanation.

25 practice questions

1. A liquid with a high vapor pressure is more dangerous to breathe around because it:

   1. A. Evaporates readily into the air
   2. B. Sinks below the water surface
   3. C. Mixes completely with water
   4. D. Needs high heat to give off vapor
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   Answer: A. Evaporates readily into the air

   Vapor pressure reflects how readily a liquid evaporates; the higher it is, the more vapor builds up above a spill and the greater the inhalation hazard. Mixing with water describes solubility, a separate property.

2. The same solvent spills at a factory on a cool morning and again on a hot afternoon. Compared with the morning spill, the afternoon spill will:

   1. A. Release less vapor, since heat breaks the solvent down
   2. B. Release the same vapor, since vapor pressure is fixed
   3. C. Release more vapor, since vapor pressure rises
   4. D. Release less vapor, since the solvent turns more dense
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   Answer: C. Release more vapor, since vapor pressure rises

   Vapor pressure increases with temperature, so warm conditions drive more of a liquid into the air and enlarge the inhalation and fire hazard. Vapor pressure is listed at a standard temperature but changes with real conditions.

3. Chlorine has a vapor density of about 2.5. After a leak at a pool supply warehouse, you should expect the gas to:

   1. A. Collect in basements, ditches, and low areas
   2. B. Rise and disperse quickly above the building
   3. C. Mix evenly from the floor to the ceiling
   4. D. Stay bound to wet surfaces near the cylinder
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   Answer: A. Collect in basements, ditches, and low areas

   A vapor density above 1 means the gas is heavier than air, so chlorine sinks and pools in low spots such as basements, trenches, and stairwells. Gases with a vapor density below 1 rise and disperse.

4. Natural gas (methane) has a vapor density of about 0.55. In a home with a gas leak, the gas will tend to:

   1. A. Settle along the floor and in the basement
   2. B. Rise toward the ceiling and upper floors
   3. C. Stay near the stove where the leak began
   4. D. Dissolve into the water in the plumbing
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   Answer: B. Rise toward the ceiling and upper floors

   Gases with a vapor density below 1, such as methane, are lighter than air and rise, collecting near ceilings and upper levels. Propane, with a vapor density of about 1.5, is the one that settles low.

5. Gasoline has a specific gravity of about 0.7 and does not mix with water. If gasoline spills into a drainage ditch filled with water, it will:

   1. A. Sink to the bottom of the ditch water
   2. B. Dissolve evenly through the ditch water
   3. C. Become nonflammable once it touches water
   4. D. Float on top and spread across the water
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   Answer: D. Float on top and spread across the water

   A specific gravity below 1 means a liquid is lighter than water, and an insoluble liquid that is lighter than water floats. Floating gasoline can spread a fire across the water surface, so flushing it with water may enlarge the hazard.

6. A worker is covered with an oily pesticide that does not mix with water. For decon, this property means you should:

   1. A. Use water alone, since soap traps the agent
   2. B. Wipe it off with a solvent such as alcohol
   3. C. Use a dilute bleach wash on the skin
   4. D. Use soap and water rather than water alone
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   Answer: D. Use soap and water rather than water alone

   Water-insoluble, oily agents are removed poorly by water alone, so a mild soap or detergent is added to lift them from the skin. Solvents such as alcohol can increase skin absorption and add a second exposure, and bleach irritates the skin without removing an oily agent better than soap and water. Soap does not trap the agent on the skin; it lifts it so the water can rinse it away.

7. The flash point of a liquid is the lowest temperature at which it:

   1. A. Gives off enough vapor to ignite
   2. B. Bursts into flame with no ignition source
   3. C. Boils and changes from liquid to gas
   4. D. Gives off heavy vapor
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   Answer: A. Gives off enough vapor to ignite

   At the flash point, a liquid produces enough vapor to flash when an ignition source is present. Igniting with no outside source occurs at the higher autoignition (ignition) temperature.

8. Gasoline has a flash point of about -43°C (-45°F). For a gasoline spill on a winter day at -10°C (14°F), this means the spill:

   1. A. Is safe to approach until it warms
   2. B. Will freeze before vapor can form
   3. C. Still gives off ignitable vapor
   4. D. Cannot burn below 0°C (32°F)
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   Answer: C. Still gives off ignitable vapor

   Because the outside temperature is well above gasoline's flash point, the liquid still produces ignitable vapor in freezing weather. Cold slows evaporation somewhat but does not remove the fire hazard.

9. The autoignition temperature of a substance is the temperature at which it:

   1. A. Gives off enough vapor to flash near a spark
   2. B. Ignites on its own with no spark or flame
   3. C. Becomes a gas
   4. D. Reaches its upper flammable limit in the air
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   Answer: B. Ignites on its own with no spark or flame

   At its autoignition temperature, a material ignites from heat alone, such as contact with a hot exhaust pipe. The flash point is the lower temperature at which vapor needs a separate ignition source.

10. A combustible gas meter in a basement reads 5% of the lower explosive limit (LEL). This reading means the atmosphere:

    1. A. Is too lean to burn but may still be toxic
    2. B. Is in the flammable range and may explode
    3. C. Is too rich to burn and needs ventilation
    4. D. Is safe to enter without respiratory protection
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    Answer: A. Is too lean to burn but may still be toxic

    Below the LEL, there is too little fuel in the air to ignite, but many gases are toxic at concentrations far below their LEL. The reading says nothing about oxygen level or toxicity, so it does not clear the space for entry.

11. Runoff from a leaking drum at a plant gives a reading of pH 13 on the hazmat team's test paper. The liquid is most likely:

    1. A. A strong acid, such as battery acid
    2. B. Nearly neutral, so safe on the skin
    3. C. A strong base, such as lye
    4. D. A weak acid like vinegar
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    Answer: C. A strong base, such as lye

    The pH scale runs from 0 to 14: 7 is neutral, values below 7 are acids, and values above 7 are bases. A pH of 13 is a strong base (alkali), such as sodium hydroxide (lye), which causes deep liquefaction burns, so skin and eye contact need prolonged water irrigation. The EPA treats a liquid with a pH of 12.5 or higher, or 2 or lower, as corrosive. Battery acid (sulfuric acid) has a pH near 1, at the other end of the scale. A neutral liquid reads about 7, and vinegar, a weak acid, reads about 2 to 3; neither fits a reading of 13.

12. Hydrogen has a flammable range of about 4% to 75% in air, and gasoline about 1.4% to 7.6%. Compared with gasoline vapor, hydrogen:

    1. A. Is less dangerous since it needs more fuel
    2. B. Cannot ignite until it reaches 75% in air
    3. C. Is too light to reach an ignition source
    4. D. Ignites over a much wider range of mixes
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    Answer: D. Ignites over a much wider range of mixes

    The width of the flammable range matters most here: a gas that burns anywhere from 4% to 75% finds an ignitable mix in far more situations than one that burns from 1.4% to 7.6%, and hydrogen also needs very little energy to ignite. Its higher LEL is the tempting point, but it does not make hydrogen safer, because hydrogen still ignites at a low concentration and over a huge range. Hydrogen ignites anywhere within that range; 75% is its upper limit, not its starting point. Hydrogen is lighter than air and rises, but it collects under ceilings and in enclosed spaces, where lights, switches, and other ignition sources are found.

13. A shed is filled with propane above its upper explosive limit (UEL). A firefighter opens the door to air it out. The danger is that:

    1. A. Opening the door makes the mixture even richer
    2. B. Dilution may bring it into the flammable range
    3. C. Air entering the shed raises the LEL of propane
    4. D. The mix above the UEL explodes with a spark
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    Answer: B. Dilution may bring it into the flammable range

    Above the UEL, a mix is too rich to burn, but adding air dilutes it down into the flammable range, where any ignition source can cause an explosion. A mix above the UEL does not ignite until enough air enters.

14. Immediately dangerous to life or health (IDLH) refers to the concentration that:

    1. A. Is the safe average limit for an 8-hour shift
    2. B. Is the maximum allowed for 15 minutes at a time
    3. C. Could kill or prevent escape within 30 minutes
    4. D. Is the level at which the odor is first noticed
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    Answer: C. Could kill or prevent escape within 30 minutes

    IDLH is the concentration that poses an immediate threat to life, causes irreversible health effects, or impairs a person's ability to escape within 30 minutes. The 8-hour average describes the PEL or TLV-TWA.

15. Air monitoring shows a toxic gas above its IDLH level in a tank room. Respiratory protection for entry must be:

    1. A. Positive-pressure supplied air, such as SCBA
    2. B. An air-purifying respirator with the right filter
    3. C. An N95 respirator with a tight face seal fit
    4. D. A powered air-purifying respirator with hood
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    Answer: A. Positive-pressure supplied air, such as SCBA

    Above IDLH, a respirator failure could be fatal, so only positive-pressure, supplied-air systems such as SCBA are allowed. Air-purifying respirators, including powered ones, filter room air and can be overwhelmed or fail.

16. The OSHA permissible exposure limit (PEL) for a chemical is best described as the:

    1. A. Level at which exposure is fatal
    2. B. Advisory limit for a 15-minute exposure
    3. C. Level at which workers can first smell it
    4. D. Legal limit for an average 8-hour workday
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    Answer: D. Legal limit for an average 8-hour workday

    The PEL is an enforceable OSHA limit, usually stated as an 8-hour time-weighted average. The ACGIH's threshold limit values are advisory, and the 15-minute limit is the short-term exposure limit (STEL).

17. The threshold limit value-ceiling (TLV-C) for a chemical is the concentration that:

    1. A. Can be averaged over an 8-hour day
    2. B. Should not be exceeded at any time
    3. C. Can be exceeded for up to 15 minutes
    4. D. Causes death in half of exposed animals
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    Answer: B. Should not be exceeded at any time

    A ceiling value must never be exceeded, even briefly, because short peaks can cause harm. The TLV-TWA is averaged over a workday, and the TLV-STEL allows a 15-minute exposure.

18. Two chemicals leak at a plant. Chemical A has a TLV of 0.5 ppm, and chemical B has a TLV of 100 ppm. Based on these values:

    1. A. B is far more toxic than A
    2. B. A is far more toxic than B
    3. C. Both are equally toxic
    4. D. Neither is a health risk
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    Answer: B. A is far more toxic than B

    Exposure limits are set lower for more toxic substances, so a TLV of 0.5 ppm signals a much more dangerous chemical than a TLV of 100 ppm. Students often reverse this, assuming a bigger number means a bigger hazard.

19. The LD50 of a chemical is the dose that:

    1. A. Causes symptoms in half of workers
    2. B. Is safe for half of a working day
    3. C. Kills half of a test animal group
    4. D. Is half the IDLH concentration
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    Answer: C. Kills half of a test animal group

    The LD50 is the dose that is lethal to 50% of exposed test animals; the lower the LD50, the more toxic the substance. LC50 is the matching term for a concentration in air.

20. A chemical's short-term exposure limit (STEL) is best described as the:

    1. A. Dose that would kill half of a group of test animals
    2. B. Average level allowed over an 8-hour workday
    3. C. Lowest concentration that a person can smell
    4. D. Highest average allowed over a 15-minute period
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    Answer: D. Highest average allowed over a 15-minute period

    The STEL is the maximum time-weighted average concentration a worker may be exposed to over a short period, usually 15 minutes, without irritation or harm, and only a few times a day. The 8-hour average is the TLV-TWA or PEL; the dose that kills half of a test group is the LD50.

21. A hazmat worker cuts his hand on a broken glass bottle that held a toxic liquid. The route of exposure is:

    1. A. Injection
    2. B. Inhalation
    3. C. Ingestion
    4. D. Absorption
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    Answer: A. Injection

    When a contaminated sharp object breaks the skin, the chemical is carried directly into the tissue, which is injection. Absorption refers to a chemical crossing intact skin or mucous membranes.

22. Responders at a hazmat incident are most likely to ingest a toxic agent by:

    1. A. Eating, drinking, or smoking in the area
    2. B. Splashes of product into the eyes
    3. C. Splashing liquid onto an exposed arm
    4. D. Leaks through a poorly fitting face piece
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    Answer: A. Eating, drinking, or smoking in the area

    Ingestion in hazmat work usually happens hand to mouth, when people eat, drink, smoke, or touch their faces before decon. Vapor that leaks past a poorly fitting face piece is inhaled, and splashes onto the skin or into the eyes are absorbed.

23. A worker who inhaled carbon tetrachloride had burning eyes at the scene and develops liver failure 3 days later. The liver failure is an example of a:

    1. A. Immediate local effect
    2. B. Delayed systemic effect
    3. C. Delayed local effect
    4. D. Immediate systemic effect
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    Answer: B. Delayed systemic effect

    Local effects occur at the point of contact, such as eye irritation, while systemic effects occur after the agent is absorbed and carried to distant organs. Liver injury days later is both systemic and delayed, which is why exposed patients need follow-up.

24. Acetone, a flammable solvent that mixes completely with water, leaks into a creek. Unlike gasoline, the acetone will:

    1. A. Float on the surface as a thin sheen
    2. B. Sink and collect on the creek bottom
    3. C. Stay pooled at the point where it entered
    4. D. Dissolve and travel through the water
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    Answer: D. Dissolve and travel through the water

    Water solubility decides what a liquid does in water before specific gravity matters. Acetone mixes fully with water, so it dissolves and moves downstream with the current, where it can reach water intakes; the mixture stays flammable until it is heavily diluted, and downstream users must be warned. Floating as a sheen is what insoluble liquids lighter than water, such as gasoline, do; acetone is also lighter than water, which makes this the tempting answer, but it dissolves instead. Sinking to the bottom is what insoluble liquids heavier than water, such as many chlorinated solvents, do. A liquid that mixes into flowing water cannot stay pooled where it entered.

25. Chlorine is shipped as a liquid under pressure. A small liquid leak from a cylinder is dangerous mainly because the liquid:

    1. A. Freezes on contact and seals off the leak
    2. B. Stays a liquid and pools near the valve
    3. C. Expands into a much larger volume of gas
    4. D. Burns at once and so leaves no vapor
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    Answer: C. Expands into a much larger volume of gas

    Liquefied gases have a high expansion ratio; liquid chlorine forms about 460 times its volume as gas, so a small liquid leak can create a large toxic cloud. Frost may form at the leak, but it does not stop the release.