Technologists created hazard rating systems (HRS) because they believed the needs of those in which they have an interest weren’t being met by the existing systems. HRS’ should effectively describe all hazards, allow comparison among chemicals, propose protection schemes, and be incredibly easy to understand and communicate.

There are five general types of HRS: 1 to 4 NFPA, safety and risk phrase, numerical, exposure limit probability, and the SAPMA system.

1-4 NFPA
The US-based National Fire Protection Association (NFPA) created the HRS most commonly known in the US. The US Department of Transportation (DOT) requires its use in the “four diamond” labels found on all chemical packages. Each diamond pertains to one of three categories of risk: health, flammability, and reactivity. The fourth diamond warns of specific hazards. Each category is divided into four levels of hazard potential with increasing numbers indicating increasing hazard. Numerical values for flammability are based on flash point. Those for health are: deadly (4), extreme danger (3), hazardous (2), slightly hazardous (1), and normal (0).

Safety and Risk Phrase
The EC through its European INventory of Existing Chemical Substances (EINECS) and the UK through its Chemical Hazard Information and Packaging for Supply (CHIPS) have separately created complex HRSs which they require to be used in package labeling and worker training.

Here, specificity is valued over simplicity and ease of communication. Hazards are classified by numbered phrases which describe a specific risk or protective method. There are more than 70 of each in both the EC and UK systems. Most MSDS sheets now contain codes such as R23 or R45 which correspond to certain “risk phrases,” and S17 or S24, which correspond to certain “safety phrases.”

In the CHIPS system, chemicals are classified differently depending upon whether they are being transported, or supplied (sold). The reasons for this are the different types of risk exhibited in different situations.

Numerical
In the 1990s, the US EPA developed the Indiana Relative Chemical Hazard Score (IRCHS). A database has been developed of rankings (scores) for more than 1,250 solvents (chemicals). They are sorted by CAS number and value. There many components, but there are two general elements: a normalized worker exposure hazard value; and a normalized environmental hazard value. The workplace hazard value has three components: the health effects; the routes of exposure; and a safety hazard value. The environmental hazard value has four components: water; air; land; and a global hazard value. Each of these seven components has sub-components.

From: “C4: Critical Cleaning For Contamination Control”