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As noted in the May 1999 Hazmat Studies column, chemicals can degrade, dehydrate or form dangerous compounds as they age. Many compounds that are normally safe may become shock- or heat-sensitive explosives when old. This can create risk for emergency response personnel.
Photo by Robert Burke
Ether containers should be dated and disposed of six months after opening.
Listed below are some common laboratory chemicals that become increasingly dangerous as they age:
Ethyl ether, and other ethers, are organic compounds that form explosive peroxides when in contact with air. They are found in college, high school, research and industrial laboratories. When a container of ether is opened, oxygen from the air bonds with the single oxygen present in each ether molecule and forms an organic peroxide.
These peroxides are very unstable, and become sensitive to shock, heat and friction. Moving or shaking a container can cause an explosion. Ethers are also very flammable, with wide flammable ranges. Fire is likely to follow an explosion of an ether container.
Ethers were once used extensively as anesthetics in hospitals and, while not highly toxic, could injure or impair emergency responders. Ethers in laboratories, should be dated when opened and discarded after six months in storage; otherwise, they run the risk of peroxide formation.
Potassium metal, a metallic element from family one on the Periodic Table of Elements, is soft and silvery in color, and frequently found in high school and college laboratories. In transport, it is found in metal containers stored under kerosene or naphtha to keep it from contact with air. While not air reactive, potassium and other metals of family one can react to the moisture in the air.
When encountered in labs, potassium and other family one metals are often stored in improper containers, such as mayonnaise or canning jars. This is dangerous - during an emergency, the glass containers can break and expose the metal to the air and spill the flammable liquid also in the container. Like other members of family one, potassium metal is a dangerous fire risk and reacts violently with water to liberate hydrogen gas (which is highly flammable). The heat from the reaction of the water and the potassium can be enough to ignite the hydrogen. When exposed to moist air, it can also ignite spontaneously.
Photo by Robert Burke
Picric acid was found in a high school chemistry lab in a dried-out and very dangerous condition.
Potassium metal is closely related to sodium and lithium metals, which are in the same family on the Periodic Table Of Elements. However, the similarity ends with their water- and air-reactive characteristics. Potassium metal becomes very dangerous in storage as it ages. Like ether, it forms explosive peroxides in long-term storage.
Potassium can form peroxides and superoxides at room temperature, and may explode violently when handled. Simply cutting a piece of potassium metal with a knife to conduct an experiment, could cause an explosion.
Potassium metal's dangers far outweigh its usefulness in lab experiments in schools and should be replaced with sodium or lithium metals, which also react with water, but do not form explosive peroxides.
Picric acid is a type of chemical that is shipped and stored with a minimum of 10% to 20% water in its container. While it is a high explosive when dry, it is classified as a 4.1 Flammable Solid, Wetted Explosive because of the moisture content in the container. It cannot be shipped when dry. As long as the moisture remains in the container, the compound is stable.
Picric acid is a yellow crystal that becomes highly explosive when it dries out and is shocked or heated. The structural and molecular formulas of picric acid, (the common name for tri-nitro phenol), and its close relative, tri-nitro toluene (TNT), are very similar. When dry, picric acid also closely resembles the explosive power of TNT pound for pound.