We all know how diamonds are formed. You take a lump of carbon and subject it to intense pressure and high temperatures and magically those carbon atoms are pressed into a diamond. The diamonds we are going to form will be a tad easier.
This month’s safety column is the third in our series on safe laboratory chemical management. Readers of our Safety Guys column were introduced to safe chemical handling with our “Planning Chemical Management for the Forensic Laboratory” article describing how to develop and implement a program for proper management of laboratory chemicals.1 As that article stated, it all begins with a complete, up to date, and accurate chemical inventory. Our second article “Making Sense of MSDS” was a tutorial on understanding material safety data sheets.2 This issue we are going to discuss the National Fire Protection Association (NFPA) hazard diamond, sometimes referred to as the fire diamond, and how to decipher the information it contains.3
Classes and the NFPA Hazard Diamond
Experienced laboratory managers know that there are four basic categories of chemicals: toxic, corrosive, flammable, and reactive. However, in our chemical world there are many additional categories and subsets of these main four. We should also keep in mind that many chemicals exhibit a combination of properties and would fall into more than a single class or category. These four properties are the foundation of the NFPA hazard diamond. Coincidentally, these four categories are the main criteria used to define wastes as hazardous under the federal Resource Conservation and Recovery Act (RCRA). The hazard diamond has gained wide acceptance and most manufacturers include it on their labels when appropriate. Figure 1 shows the layout of the different sections and our discussion will start at the top and work clockwise around the diamond.
Figure 1: NFPA Hazard Diamond
The top of the diamond indicates the flammability hazard. The chemical is rated from zero to four. A zero means the material will not burn under most common circumstances. Examples include hydrogen peroxide and sodium hydroxide. A one indicates the material will ignite and burn at temperatures greater than 200°F. Materials that fall into this category are glycerine and propylene glycol. A two indicates substances that will burn at temperatures less than 200°F like naphthalene, octyl alcohol, and nitrobenzene. A rating of three denotes materials with flashpoints below 100°F such as xylene, amyl acetate, and butyl alcohol. Finally, a four indicates extremely flammable substances. These are things like acetone, ethyl ether, acetylene, and cyclohexane.
Flammability may be the single most hazardous characteristic causing more injuries and damage than any of the others in the diamond. If there is anything other than a zero in this part of the diamond make sure to use this material with adequate ventilation, clean up spills immediately, and above all, keep heat and flame well away from the area of use.
Moving clockwise, as promised, the next part of the hazard diamond designates the potential reactivity of the material, which is also rated from zero to four. Zero indicates a stable chemical under most conditions, even fire. Substances that are normally stable but can become unstable when heated or may react with water, but not violently, are rated a one. Chemicals that are rated a two are normally unstable and readily undergo violent decomposition. They may also react violently with water. Materials with a rating of three are capable of an explosive reaction or detonation if subjected to a strong initiating source such as heat or shock. A four indicates substances that are readily capable of explosive decomposition or detonation at normal temperatures.
For illustration of the reactivity, consider the following examples. Liquid nitrogen would receive a zero rating. It is stable, non-flammable, and non-reactive with water. Phosphorus (red or white) is rated a one since it can become unstable at elevated temperatures. Calcium metal rates a two. Less reactive than sodium, it reacts violently with water, alcohols, and other materials and burns in air. Fluorine gas is an example of reactive material rating a three. It is the most reactive non-metal, decomposes in water producing hydrofluoric acid and other hazardous compounds, and reacts vigorously with most oxidizable substances at room temperature, usually with ignition. An example of a class four reactive substance is trinitrotoluene or TNT. We are all familiar with its explosive properties.