The hazard rating index on an HMIS (Hazardous Materials Identification System) label is a numerical scale from 0 to 4 that tells you how dangerous a chemical is across three categories: health, flammability, and physical hazard. A rating of 0 means minimal risk, while 4 means severe or life-threatening danger. Each category is color-coded on a rectangular label you’ll typically see on chemical containers in workplaces.
What the Numbers Mean
Every HMIS label rates a chemical on a simple five-point scale:
- 0: Minimal hazard. The material poses little to no risk under normal handling conditions.
- 1: Slight hazard. Minor irritation or injury is possible, but the risk is low.
- 2: Moderate hazard. Temporary or minor injury could result from exposure or mishandling.
- 3: Serious hazard. The material can cause major injury or significant health effects, even with brief exposure.
- 4: Severe hazard. Exposure or contact can be life-threatening or cause permanent damage.
This same 0 to 4 scale applies to each of the three hazard categories on the label. A chemical might score a 3 for health risk but only a 1 for flammability, giving you a quick snapshot of where the real dangers lie.
The Three Color-Coded Categories
The HMIS label uses colored horizontal bars, each representing a different type of hazard.
The blue bar covers health hazards. This rating reflects the chemical’s toxicity, including how harmful it is if inhaled, swallowed, or absorbed through the skin. The rating is based on the chemical’s inherent toxicity rather than the specific way you’re using it. In the current version of HMIS, the health bar includes a space for an asterisk (*) next to the number. If you see that asterisk, the chemical poses a chronic health hazard, meaning long-term exposure could cause problems like lung disease or kidney damage, not just immediate effects.
The red bar covers flammability. This tells you how easily the material can catch fire. A chemical rated 4 could ignite at room temperature or below, while a 0 won’t burn under normal conditions. The flammability criteria align with the standards set by the National Fire Protection Association (NFPA 704).
The orange bar (or yellow, depending on the version) covers physical hazards. In earlier versions of HMIS, this category was labeled “reactivity” and focused on whether a chemical could violently react, decompose, or explode. The current fourth edition, revised in 2014, broadened this to “physical hazard” and now includes eight subcategories: explosives, oxidizers (solids, liquids, and gases), gases under pressure, self-reactive substances, self-heating substances, water-reactive materials, organic peroxides, and substances corrosive to metal. This update aligned HMIS with the Globally Harmonized System (GHS) used in modern Safety Data Sheets.
The Personal Protection Section
Below the three hazard bars, HMIS labels include a white section showing what personal protective equipment (PPE) you need when handling the chemical. Instead of a number, this section uses a letter code from A through K, each specifying a different combination of gear:
- A: Safety glasses
- B: Safety glasses and gloves
- C: Safety glasses, gloves, and apron
- D: Face shield, gloves, and apron
- E: Safety glasses, gloves, apron, and dust respirator
- F: Safety glasses, gloves, apron, and dust/vapor respirator
- G: Safety glasses, gloves, and vapor respirator
- H: Splash goggles, gloves, apron, and vapor respirator
- I: Safety glasses, gloves, and dust/vapor respirator
- J: Splash goggles, gloves, apron, and dust/vapor respirator
- K: Airline hood or mask, gloves, full suit, and boots
- X: Special handling required. Check with your supervisor or standard operating procedure.
The progression from A to K roughly tracks with increasing hazard levels, though the specific equipment varies based on whether the main risk is splashes, dust, vapors, or full-body exposure. Code K represents the highest level of protection, essentially a fully enclosed suit with its own air supply.
How HMIS Differs From the NFPA Diamond
You may have seen the diamond-shaped labels with similar color coding and numbers on buildings or storage tanks. Those are NFPA 704 labels, and while they look related, they serve a different audience. HMIS labels are designed for workers who handle chemicals daily. NFPA diamonds are designed for emergency responders, particularly firefighters, who need to assess hazards quickly during an emergency.
Both systems use the same 0 to 4 scale and share the blue (health), red (flammability), and yellow (reactivity) color scheme. But HMIS adds the PPE section, which NFPA does not. NFPA includes a white section for special notices (like water reactivity or oxidizer warnings), while HMIS uses that space for protective equipment guidance. The two systems can also assign different numbers to the same chemical because they evaluate hazards from different perspectives: routine workplace exposure versus emergency fire response.
Where HMIS Labels Fit in Workplace Safety
HMIS labels are not required by OSHA, but they are widely used as a supplemental workplace labeling system. OSHA allows employers to use HMIS labels on workplace containers as long as the labels are consistent with the Hazard Communication Standard and employees have immediate access to detailed hazard information through Safety Data Sheets. Employers who use HMIS labeling are required to train workers so they understand what the ratings, colors, and PPE codes mean.
The fourth edition of HMIS was specifically updated to align with GHS classification, which is the international system OSHA adopted in 2012 for chemical labeling. Comparison tables in the HMIS implementation manual let employers convert GHS hazard classifications directly into HMIS ratings for health, flammability, and physical hazards. This means the numbers on an HMIS label should correspond to the hazard information on a chemical’s Safety Data Sheet, giving you a consistent picture regardless of which system you’re reading.