Safety 4 Noobs

They exist in your homes, at the bar, at the grocery store, when you need to refuel your car at the gas station, and at your workplace. Flammable liquids are everywhere! You’ve probably heard of ethanol, methanol, isopropyl alcohol, acetone, gasoline, diesel, ether, and turpentine. So what makes these chemicals flammable?

OSHA’s and the NFPA’s definition of flammable liquids is a liquid having a flash point < 140 ^oF (60 ^oC) and depends on its flashpoint and boiling point.

• Class IA flammable liquid is a liquid with a flashpoint < 73 ^oF (22.8 ^oC) and a boiling point < 100 ^oF (37.8 ^oC).
• Class IB flammable liquid is a liquid with a flashpoint <73 ^oF (22.8 ^oC) and a boiling point > 100 ^oF (37.8 ^oC).
• Class IC flammable liquid is a liquid with a flashpoint ≥ 73 ^oF (22.8 ^oC) and < 100 ^oF (37.8 ^oC)

When the flashpoint of the liquid is > 100 ^oF (37.8 ^oC) and < 140 ^oF (60 ^oC) it will be defined as the following:

• Class II combustible liquid is a liquid with a flashpoint > 100 ^oF (37.8 ^oC) and < 140 ^oF (60 ^oC)
• Class IIIA combustible liquid is a liquid with a flashpoint ≥ 140 ^oF (60 ^oC) and < 200 ^oF (93.3 ^oC)
• Class IIIB combustible liquid is a liquid with a flashpoint ≥ 200 ^oF (93.3 ^oC)

So let’s look at the chemicals listed before:

• ethanol – flashpoint: 57 F, boiling point: 173 F, so it’s a Class IB flammable liquid
• methanol – flashpoint: 53 F, boiling point: 149 F, so it’s a Class IB flammable liquid
• isopropyl alcohol – flashpoint: 53 F, boiling point: 180 F, so it’s a Class IB flammable liquid
• acetone – flashpoint: -4 F, boiling point: 133 F, so it’s a Class IB flammable liquid
• gasoline – flashpoint: -45 F, boiling point: 170 F, so it’s a Class IB flammable liquid
• diesel – flashpoint: 126 F, boiling point: 355 F, so it’s a Class II combustible liquid
• ether – flashpoint: -49 F, boiling point: 94 F, so it’s a Class IB flammable liquid
• turpentine – flashpoint: 95 F, boiling point: 309 F, so it’s a Class IB flammable liquid

So most of the common chemicals are class IB flammable liquids with diesel being a combustible liquid.

Many of these flammable liquids have densities below 1 g/ml which means that they would float on water. Along with this, their vapor densities are greater than 1 which means that they will sink in air.

This becomes very dangerous as the vapors can gather in low spots and accumulate. If there is not enough ventilation then there are chances of flashbacks happening. Ensure that these vapors are adequately ventilated and make sure that no ignition sources are not nearby.

We need to look at the vapor pressure of the chemical to determine its volatility. Vapor pressure has an inverse relationship with boiling point so if the boiling point is low then we can assume that the vapor pressure will be very high. Vapor pressure is the pressure exerted by the liquid against atmospheric pressure. When that pressure of the vapor is > than atmospheric pressure then the vapor will escape. So understanding vapor pressure is important when working with flammable liquids.

If a fire occurs from flammable liquids then it is classified as a Class B fire, so make sure that you use a class B fire extinguisher.