9.1 GHS Hazard Classification: Health and Physical Hazard Criteria

GHS Hazard Classification: Health and Physical Hazard Criteria

The fundamental cornerstone of occupational disease prevention is the systematic identification, classification, and communication of chemical and physical hazards in the workplace. In the United States, the primary regulatory instrument governing this process is the OSHA Hazard Communication Standard (HCS), codified in 29 CFR 1910.1200. In 2012, OSHA substantially revised the HCS to align with the United Nations Globally Harmonized System of Classification and Labelling of Chemicals (UN GHS), transitioning from a performance-oriented standard ("Right to Know") to a standardized, criteria-driven classification and communication framework ("Right to Understand").

For Certified Industrial Hygienist (CIH) candidates, mastering the quantitative cutoffs for health and physical hazard classifications, label specifications, the 16-section Safety Data Sheet (SDS) architecture, and emergency trade secret disclosure protocols is critical for board examination success and professional practice.

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1. Regulatory Framework: OSHA 29 CFR 1910.1200 & GHS Evolution

The OSHA Hazard Communication Standard establishes a comprehensive downstream information transfer system:

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|                   HAZARD COMMUNICATION INFORMATION FLOW                 |
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|                                                                         |
|  [ CHEMICAL MANUFACTURER / IMPORTER ]                                   |
|  - Classifies chemical hazards using standardized GHS criteria          |
|  - Authors standardized 16-Section Safety Data Sheets (SDSs)            |
|  - Generates compliant container labels with pictograms & H/P-codes     |
|                                    |                                    |
|                                    v (Shipped with chemicals)           |
|  [ DOWNSTREAM EMPLOYER / INDUSTRIAL HYGIENIST ]                         |
|  - Maintains Written HazCom Program                                     |
|  - Maintains complete, accessible SDS library (electronic or hardcopy)  |
|  - Ensures all in-plant containers are properly labeled                 |
|  - Conducts comprehensive worker training prior to initial assignment   |
|                                    |                                    |
|                                    v                                    |
|  [ EXPOSED WORKFORCE ]                                                  |
|  - Understands physical & health risks, pictograms, and safe handling   |
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The Core Mandates of 29 CFR 1910.1200

1. Hazard Classification: Chemical manufacturers and importers must evaluate the scientific evidence regarding chemical substances and mixtures to classify their physical and health hazards against established numeric and qualitative criteria.
2. Written HazCom Program: Employers must develop, implement, and maintain at each workplace a written hazard communication program detailing chemical inventories, labeling systems, SDS management, non-routine task hazards, and contractor coordination.
3. Safety Data Sheets (SDSs): Standardized, 16-section technical documents authored by the manufacturer/importer that must be readily accessible to employees during every work shift.
4. Standardized Shipped Labels: Container labels containing six specific elements, including harmonized signal words, hazard statements, precautionary statements, and pictograms.
5. Employee Training: Initial and refresher training covering chemical hazard recognition, operations where hazardous chemicals are present, methods to detect the presence or release of chemicals, physical and health hazards, and protective measures (engineering controls, work practices, and PPE).

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2. Health Hazard Classifications & Quantitative Cutoff Criteria

Under GHS and OSHA HCS, a health hazard is defined as a chemical for which there is statistically significant evidence based on at least one study conducted in accordance with established scientific principles that acute or chronic health effects may occur in exposed employees. The standard delineates 10 discrete health hazard classes, many of which are subdivided into numeric categories based on toxicological potency.

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|                      THE 10 GHS HEALTH HAZARD CLASSES                   |
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|  1. Acute Toxicity (Oral, Dermal, Inhalation Gas/Vapor/Dust-Mist)       |
|  2. Skin Corrosion / Irritation (Categories 1A, 1B, 1C, 2)              |
|  3. Serious Eye Damage / Eye Irritation (Categories 1, 2A, 2B)          |
|  4. Respiratory or Skin Sensitization (Category 1, 1A, 1B)              |
|  5. Germ Cell Mutagenicity (Categories 1A, 1B, 2)                       |
|  6. Carcinogenicity (Categories 1A, 1B, 2)                              |
|  7. Reproductive Toxicity (Categories 1A, 1B, 2 & Lactation)            |
|  8. Specific Target Organ Toxicity - Single Exposure (STOT-SE 1, 2, 3)  |
|  9. Specific Target Organ Toxicity - Repeated Exposure (STOT-RE 1, 2)   |
| 10. Aspiration Hazard (Category 1)                                      |
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2.1 Acute Toxicity Classification Cutoffs

Acute toxicity refers to those adverse effects occurring following oral or dermal administration of a single dose of a substance, or multiple doses given within 24 hours, or an inhalation exposure of 4 hours. Substances are allocated to one of four toxicity categories based on numeric LD50 (oral, dermal) or LC50 (inhalation) values:

Exam Key Concept — Acute Toxicity Estimate (ATE) for Mixtures: When testing data are unavailable for a multi-component chemical mixture, the Acute Toxicity Estimate (ATE) of the mixture is calculated using the harmonic additivity formula:

$\frac{100}{\text{ATE}_{\text{mix}}} = \sum_{i=1}^{n} \frac{C_i}{\text{ATE}_i}$

Where Ci is the concentration of ingredient i (w/w% or v/v%), and ATEi is the acute toxicity cutoff or point estimate for ingredient i. Ingredients present at < 1% (or < 0.1% for carcinogens/sensitizers) are excluded unless they drive mixture toxicity.

2.2 Skin Corrosion / Irritation

• Skin Corrosion (Category 1): The production of irreversible damage to the skin; namely, visible necrosis through the epidermis and into the dermis following exposure of up to 4 hours. Subcategories are determined by exposure and observation durations:
  • Category 1A: Corrosive response occurs following exposure ≤ 3 minutes and observation up to 1 hour.
  • Category 1B: Corrosive response occurs following exposure > 3 minutes to ≤ 1 hour and observation up to 14 days.
  • Category 1C: Corrosive response occurs following exposure > 1 hour to ≤ 4 hours and observation up to 14 days.
• Skin Irritation (Category 2): The production of reversible damage to the skin following application of an agent for up to 4 hours. Characterized by a mean Draize score ≥ 2.3 for erythema/eschar or edema in at least 2 of 3 tested animals, which fully resolves within an observation period of 14 days.

2.3 Serious Eye Damage / Eye Irritation

• Serious Eye Damage (Category 1): The production of tissue damage in the eye, or serious physical decay of vision, following application of a test substance to the anterior surface of the eye, which is not fully reversible within 21 days of application (corneal opacity, iritis, conjunctival necrosis).
• Eye Irritation (Category 2 / 2A / 2B): Production of changes in the eye following application which are fully reversible within 21 days:
  • Category 2A (Irritating to eyes): Reversible within 21 days (Draize corneal opacity ≥ 1, iritis ≥ 1, or conjunctival redness ≥ 2).
  • Category 2B (Mildly irritating to eyes): Reversible within 7 days of application.

2.4 Respiratory and Skin Sensitization

• Respiratory Sensitizer (Category 1): A substance that will lead to hypersensitivity of the airways following inhalation (occupational asthma, eosinophilia). Subdivided into Category 1A (high potency in humans or animals at low exposure concentrations) and Category 1B (low-to-moderate potency).
• Skin Sensitizer (Category 1): A substance that will induce an allergic response following skin contact (allergic contact dermatitis). Evaluated via animal bioassays (Local Lymph Node Assay [LLNA], Guinea Pig Maximization Test [GPMT]). In the LLNA, an EC3 value (effective concentration producing a 3-fold stimulation index) ≤ 2% designates Category 1A (strong sensitizer); an EC3 > 2% designates Category 1B.

2.5 Germ Cell Mutagenicity

• Category 1A: Substances known to induce heritable mutations in human germ cells based on positive evidence from human epidemiological studies.
• Category 1B: Substances to be regarded as if they induce heritable mutations in the germ cells of humans (positive in vivo heritable germ cell mutagenicity tests in mammals, or positive in vivo somatic mutagenicity tests combined with evidence that the chemical interacts with germ cells).
• Category 2: Substances that cause concern for humans owing to the possibility that they may induce heritable mutations in human germ cells (positive in vivo somatic mammalian mutagenicity tests, or in vitro mutagenicity with chemical structure-activity relationships).

2.6 Carcinogenicity

• Category 1A: Known to have carcinogenic potential for humans; classification is largely based on human epidemiological evidence (e.g., benzene, asbestos, crystalline silica).
• Category 1B: Presumed to have carcinogenic potential for humans; classification is largely based on demonstrated animal carcinogenicity (e.g., formaldehyde, vinyl bromide).
• Category 2: Suspected human carcinogens; evidence obtained from human or animal studies is suggestive but not sufficient to place the substance in Category 1A or 1B (e.g., methylene chloride under certain criteria, titanium dioxide respirable particles).

2.7 Reproductive Toxicity

Includes adverse effects on sexual function and fertility in adult males and females, as well as developmental toxicity in offspring.

• Category 1A: Known human reproductive toxicant based on human evidence (e.g., lead, thalidomide).
• Category 1B: Presumed human reproductive toxicant based on experimental animal data (e.g., 2-ethoxyethanol, phthalate esters).
• Category 2: Suspected human reproductive toxicant.
• Effects on or via Lactation: A separate, unnumbered category for substances absorbed by women and transferred to breast milk in quantities sufficient to threaten infant health (e.g., polychlorinated biphenyls, dioxins).

2.8 Specific Target Organ Toxicity — Single Exposure (STOT-SE)

• STOT-SE Category 1: Substances that produce significant, non-lethal, irreversible or severe toxic effects in humans, or shown to produce significant toxicity in experimental animals at low oral guidance doses (≤ 300 mg/kg) following a single exposure (e.g., methanol-induced optic nerve atrophy).
• STOT-SE Category 2: Substances that produce significant non-lethal toxicity in experimental animals at moderate guidance doses (300 to 2000 mg/kg) following a single exposure.
• STOT-SE Category 3: Transient target organ effects—specifically respiratory tract irritation (coughing, pain) or narcotic effects (drowsiness, impaired reflexes, dizziness, central nervous system depression).

2.9 Specific Target Organ Toxicity — Repeated Exposure (STOT-RE)

• STOT-RE Category 1: Substances that have produced significant toxic morbidity or organ damage in humans, or shown to produce significant toxicity in experimental animals following repeated subchronic exposure at low guidance doses (oral rat 90-day study: ≤ 10 mg/kg/day; inhalation vapor: ≤ 0.2 mg/L/6hr/day; inhalation dust: ≤ 0.02 mg/L/6hr/day), such as carbon tetrachloride hepatotoxicity or n-hexane peripheral neuropathy.
• STOT-RE Category 2: Substances that produce significant toxicity following repeated subchronic exposure at moderate guidance doses (oral rat 90-day study: 10 to 100 mg/kg/day; inhalation vapor: 0.2 to 1.0 mg/L/6hr/day).

2.10 Aspiration Hazard

• Aspiration Hazard Category 1: Substances known to cause human aspiration toxicity (chemical pneumonitis, pulmonary edema, or death following entry of liquid directly through the oral/nasal cavity into the trachea and lower respiratory tract), or liquid hydrocarbons that have a kinematic viscosity ≤ 20.5 mm²/s measured at 40°C (e.g., gasoline, kerosene, Stoddard solvent).

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3. Physical Hazard Classifications

Under 29 CFR 1910.1200 Appendix B, physical hazards are evaluated across 16 hazard classes. A critical focus for industrial hygiene calculations is the classification of flammable liquids and combustible chemical mixtures.

3.1 Flammable Liquid Categories

Flammable liquids are classified into four distinct categories based on their Flash Point (FP) and Initial Boiling Point (BP):

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|                  GHS FLAMMABLE LIQUID CLASSIFICATION                    |
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|                                                                         |
|   Category 1: Flash Point < 23°C (73.4°F) AND Boiling Point ≤ 35°C     |
|               (Extremely flammable liquid and vapor)                    |
|                                                                         |
|   Category 2: Flash Point < 23°C (73.4°F) AND Boiling Point > 35°C     |
|               (Highly flammable liquid and vapor)                       |
|                                                                         |
|   Category 3: Flash Point ≥ 23°C (73.4°F) AND ≤ 60°C (140°F)           |
|               (Flammable liquid and vapor)                              |
|                                                                         |
|   Category 4: Flash Point > 60°C (140°F) AND ≤ 93°C (199.4°F)           |
|               (Combustible liquid)                                      |
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3.2 Other Major Physical Hazard Classes

• Pyrophoric Liquids and Solids: Substances that, even in small quantities, ignite within 5 minutes after coming into contact with air (e.g., triethylaluminum, white phosphorus). Signal word: Danger; Pictogram: Flame.
• Self-Heating Substances: Solid or liquid substances, other than pyrophorics, which by reaction with air and without energy supply, are liable to self-heat (Categories 1 and 2).
• Organic Peroxides: Thermally unstable liquid or solid organic substances containing the bivalent -O-O- peroxy structure. Divided into seven types (Type A to Type G):
  • Type A: Can detonate or deflagrate rapidly as packaged (Exploding Bomb; Danger).
  • Type B: Possesses explosive properties and can detonate partially (Exploding Bomb + Flame; Danger).
  • Types C & D: Possesses explosive properties but cannot detonate (Flame; Danger).
  • Types E & F: Low explosive power when heated under confinement (Flame; Warning).
  • Type G: Thermally stable, no explosive properties (exempt from organic peroxide hazard class).
• Oxidizing Liquids / Solids / Gases: Substances that, while in themselves not necessarily combustible, may, generally by yielding oxygen, cause or contribute to the combustion of other materials (Categories 1, 2, 3). Pictogram: Flame Over Circle.
• Gases Under Pressure: Gases contained in a receptacle at a pressure ≥ 200 kPa (29 psi) at 20°C. Subdivided into: Compressed gas, Liquefied gas, Refrigerated liquefied gas, and Dissolved gas. Pictogram: Gas Cylinder.
• Corrosive to Metals: Substances that by chemical action will materially damage or destroy metals (corrosion rate on steel or aluminum > 6.25 mm/year at 55°C). Pictogram: Corrosion.

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