Are flammable or combustible liquids hazardous to human health?

The short answer to this question is yes, both flammable and combustible liquids are hazardous to the health of humans due to the high possibility of igniting a fire or initiating an explosion. There can be other dangers associated with these chemicals as well if they are breathed in, ingested, or splashed onto the skin or eyes.

Now that we’ve established the “why” these hazardous substances are dangerous, let’s dive into the question of “how.” First, we must go over a handful of definitions.

OSHA’s definition of “chemical” in its Hazard Communication Standard is “any element, chemical compound, or mixture of elements and/or compounds.” This is a broad definition of chemicals, luckily OSHA has identified several categories that do not receive coverage under the regulation. You can find that list here.

Under the umbrella of “chemicals,” OSHA defines hazardous chemicals as ones that pose a physical hazard or a health hazard to the people that encounter them.

That said, both flammable liquids and combustible materials pose a physical hazard to employees. It must also be noted that even though the first category that these substances fall into is a physical hazard, there are some chemicals that also pose a significant health hazard, such as toxicity. Some examples include:

  • Benzene – Present in the plastics industry as well as a byproduct of fuel combustion, benzene is highly flammable. When accidentally inhaled or ingested, the victim can experience a wide variety of symptoms including tremors, convulsions, vomiting, confusion, etc. The longer-term affects can include leukemia, anemia, fertility problems, and immune system issues.
  • Acetone – Used in both dermatology and in labs, the risk of igniting a fire is high with its low flash point of -20°C. In lower exposures, acetone can result in lethargy, headache, dizziness, fainting, etc. If exposed in large amounts, acetone poisoning can occur and have adverse long-term health effects such as infertility, birth defects, damage to the kidneys, liver, and nerves, as well as the potential of entering a coma.
  • Pentane – Used as a fuel or solvent, pentane evaporates quickly and has a flash point of -49°C. When exposed, the victim may suffer from eye and skin irritation, headaches, dizziness, or fainting. Long-term exposure can lead to more serious ailments including nerve damage, skin issues, and pulmonary edema.

Overall, yes, both flammable and combustible hazards are damaging physically. But the vapors, solids, or liquids from these chemicals can also be hazardous to human health in the event of high exposure.

The Hazardous Properties of Combustible Liquids and Flammable Liquids

The reaction between both flammable and combustible liquids when given contact to the right conditions (oxygen and an ignition source) can be devastating. It may also be surprising to know that it’s not the liquids themselves that are flammable or combustible, but the vapors they emit into the air.

Volatile materials can be incredibly sensitive to temperature. The flash point is known as the lowest temperature in which a flammable or combustible vapor can ignite in the presence of a flame or spark. Some volatile substances can reach this point at negative temperatures and even well past 200 degrees Fahrenheit.

Liquid Hazard Classifications vs. Combustible Liquid Classifications

According to the NFPA, there are six classes that chemical substances can fall into when it comes to being either combustible or flammable. These classifications are based upon both the flash point of the chemical as well as its boiling point.

The NFPA flammable classes are as follows:

  • Class IA – A flash point of less than 73°F and a boiling point of less than 100°F
  • Class IB – A flash point of less than 73°F and a boiling point equal to or greater than 100°F
  • Class IC – A flash point equal to or greater than 73°F, but less than 100°F

The NFPA hazard classification for combustible liquids is as follows:

  • Class II – A flash point equal to or greater than 100°F, but less than 140°F
  • Class IIIA – A flash point equal to or greater than 140°F, but less than 200°F
  • Class IIIB – A flash point equal to or greater than 200°F

OSHA has its own hazard numbering system for only flammable materials. OSHA does not use the term combustible in its regulatory literature. In the HCS from OSHA, they describe four categories of flammable chemicals. These are as follows:

  • Category 1 – These liquids have flash points below 73.4°F and a boiling point at or below 95°F.
  • Category 2 – These liquids have flashpoints below 73.4°F and a boiling point above 95°F.
  • Category 3 – These liquids have flashpoints at or above 73.4°F and at or below 140°F.
  • Category 4 – These liquids have flash points above 140°F and at or below 199.4°F.

Knowing and establishing either classification system for flammable or combustible materials is essential for worker safety. These numbers can be placed on numerous different labels, such as GHS labels, on safety data sheets, and on visual signage for chemical storage areas.

Remember, the more information given to employees, the better they can protect themselves from dangerous hazards.

How to Prioritize the Safety and Health of Employees

Prioritizing human health in the presence of these dangerous liquids comes with three primary elements:

Flammable and combustible liquids are no joke when it comes to harming human health. Not only do they pose a fire risk, but many volatile chemicals are also toxic in high enough quantities to cause permanent bodily damage or even fatalities.


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