Necessary Chemistry

A material safety data sheet (MSDS)—a component of the Occupational Safety and Health Administration’s Hazard Communication standard—provides workers and emergency responders with safe procedures for handling or working with a particular substance. An MSDS contains a huge amount of information that can be very challenging for a chemist, much less someone on the average construction job site. However, reviewing an MSDS for a common chemical hazard will make it easier to understand its content and value for all chemicals.

It’s important to note that no format exists for MSDSs. Although OSHA requires a minimum amount of information and has provided a recommended format—OSHA 174—other formats were and still are accepted. In fact, in recent years, OSHA has recommended using the American National Standards Institute (ANSI) version.

The OSHA 174 format contains seven sections beginning with the manufacturer’s information and ending with control measures. The ANSI MSDS contains 16 sections beginning again with manufacturer information but ending with a general section for other information. Regardless of format, the key is to focus on the important content, understand it and be able to use it.

Knowing how to read an MSDS could help avoid dangerous situations. Having the manufacturer’s emergency contact, the chemical’s health effects, first aid procedures, storage and disposal information, and the substance’s physical data, such as melting point and boiling point, could save lives. Much will be straightforward on the MSDSs. Little explanation is needed in reviewing the first aid procedure section, as these guidelines usually are very specific. Other technical information may seem more difficult but can be as valuable.

The section on the chemical’s identity can be very revealing. Common substances, including gasoline, can be made up of other ingredients. Benzene, a cancer-causing agent, can be found in gasoline. As you review the identity, you will see the percentage found in the substance and the exposure limits to the chemical. Exposure limits are usually identified as threshold limit value or permissible exposure limit. These are time-weighted averages based on eight-hour work shifts. Although it takes monitoring of the workplace to determine exposure level, the numbers provide an indication of the relative danger. The lower the number, the easier you can be exposed to dangerous levels. Measurements listed in short-term exposure limit reveal that even short periods of exposure can be dangerous.

Looking into the Physical and Chemical Characteristics section helps you identify the presence of a chemical and predict hazards. The appearance and odor of gasoline are described as a “translucent, straw-colored or light-yellow liquid” with a “strong, characteristic aromatic hydrocarbon odor.” Its vapor density is three to four. This is its relative weight as compared to air. The density of air is one. Therefore, gasoline vapors are heavier than air, indicating they may sink or be found at lower levels, such as down elevator shafts or in ditches. Its specific gravity or relative weight compared to water and solubility describe how it interacts with water. Gasoline has a specific gravity of less than one. This means it will float on water. Gasoline’s solubility is almost zero. It will not mix with water. This knowledge is useful in the event of a gasoline fire. Using water to attempt to put it out is not a good idea.

The section on a substance’s fire and explosion data or firefighting measures usually provides easily understood information. For gasoline, it describes the firefighting needs as “extinguisher suitable for Class B fires, dry chemical, CO2, water spray, fire fighting foam, or Halon.” It provides more technical data, such as flash point and explosive limits. Flash point is the lowest temperature at which the chemical will ignite in air. Gasoline’s is –45ºF. This makes it nearly impossible to start gasoline engines in extremely cold climates. The gasoline does not emit enough vapor to ignite. It also reveals, even at low temperatures, enough vapor can be in the air for a fire. The explosive limits of gasoline (lower limit 1.4 percent) reveals small amounts are needed in the air for a fire or explosion. When dealing with a chemical’s flammability hazard, consider both the straightforward information and the technical data.

The reactivity section is another important section that generally contains easily understood information and technical data. It identifies other chemicals that will react negatively with the substance. Mixing gasoline with oxidizers or substances that give off oxygen can cause explosive mixtures. The technical complexity comes with two words: polymerization and decomposition. Polymerization simply means a substance can transform itself. Its molecules link forming chains or polymers. However, gasoline will not form hazardous polymers. Many chemicals will decompose by themselves or decompose through a reaction, such as a fire. Gasoline will decompose through fire or when mixed with nitric acid, but this creates other hazardous chemicals.

Reading MSDSs will better prepare you to work safely. The basic information and technical data can prove useful. Take time with them. Consider what the technical data reveals about how the chemical will be present or used in the workplace and how it will act. If an emergency occurs, know where the MSDSs are located and where to find the necessary emergency information.

KELLY is a safety and health specialist with Intec, a safety consulting, training and publishing firm that offers on-site assistance and produces manuals, training videos and software for contractors. She can be reached at 800.745.4818 or Joe O’Connor edited this article.

About the Author

Diane Kelly

Safety Columnist
Diane Kelly is a safety and health specialist with Intec, a safety consulting, training and publishing firm that offers on-site assistance and produces manuals, training videos and software for contractors. She can be reached at 800.745.4818 or dkell...

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