| H₂0₂ | Hydrogen Peroxide |
| H2O | Water |
| H2S | Hydrogen Sulfide |
| HA | Health Advisory |
| HAAs | Haloacetic Acids |
| HAB | Harmful Algal Bloom |
| HACCP | hazard analysis critical control point system |
| HAP | Hazardous Air Pollutant |
| HAP ABA | Hazardous Air Pollutant Auxiliary Blowing Agent |
| HAP Applied | Hazardous Air Pollutant Applied |
| HAP Based Adhesive | Hazardous Air Pollutant Based Adhesive |
| HAP Metal | Hazardous Air Pollutant Metal |
| HAP Transfer Vehicle | Hazardous Air Pollutant Transfer Vehicle |
| HAP Used | Hazardous Air Pollutant Used |
| HAP-Based | Hazardous Air Pollutant-Based |
| HAPEM | Hazardous Air Pollutant Exposure Model |
| HAPs | Hazardous Air Pollutants |
| HASP | Health and Safety Plan |
| HAV | Hepatitis A Virus |
| HAWT | Horizontal-Axis Wind Turbine |
| Hazardous Substance UST System | Hazardous Substance Underground Storage Tank System |
| Hazardous Waste HCl Production Furnace | Hazardous Waste Hydrochloric Acid Production Furnace |
| HAZMAT | Hazardous Material |
| HB | Hierarchical Bayesian |
| HBFC | Hydrobromofluorocarbon |
| HBFCs | Hydrobromofluorocarbons |
| HC | Hazardous Constituents; Hydrocarbons (Chemicals) |
| HC Fuel CECS | Hydrocarbon Fuel-Based Combustion Emission Control System |
| HCB | Hexachlorobenzene |
| HCFC | Hydrochlorofluorocarbon |
| HCFCs | Hydrochlorofluorocarbons |
| HCHO | Formaldehyde |
| HCl | Hydrogen Chloride |
| HCS | Hazard Communication Standard |
| HCT | Hematocrit Measurement |
| HDD | Heating Degree Day |
| HDDE | Heavy-duty Diesel Engine |
| HDE | Heavy Duty Truck Engine; Heavy-duty Engine; Heavy-duty Truck; Vehicle Engine |
| HDGE | Heavy-duty Gasoline Engine |
| HDPE | High Density Polyethylene |
| HDT | Heavy-duty Truck; Highest Dose Tested |
| HDTV | High Definition Television |
| HDV | Heavy-duty Vehicle |
| HEA | Habitat Equivalency Analysis |
| HEC | Human Equivalent Concentration |
| HED | Human Equivalent Dose |
| HEID | Health and Environmental Impacts Division |
| HEL | Highly Erodible Land |
| HELs | highly erodible lands |
| HEM | Human Exposure Model |
| HEPA | High efficiency particulate air |
| HEPA filter | High Efficiency Particulate Air Filter |
| HERS index | Home Energy Rating System index |
| HEV | Hybrid Electric Vehicle |
| HEX-BCH | 1,2,3,4,7,7-Hexachloronorbornadiene |
| HFC | Hydrofluorocarbon |
| HFCs | Hydrofluorocarbons |
| HFEs | Hydrofluoroethers |
| HFET | Highway Fuel Economy Test Procedure |
| HFO | Hydrofluoroolefin |
| HFOs | Hydrofluoroolefins |
| HFPO | Hexafluoropropylene Oxide |
| Hg | Mercury and Mercury Compounds |
| Hgb | Hemoglobin |
| HGL | Hydrocarbon Gas Liquid |
| HGM | Hydrogeomorphic |
| HGM approach | Hydrogeomorphic approach |
| HGT | Horizontal Gene Transfer |
| HHV | Higher heating value |
| HHW | Household Hazardous Waste |
| HI | Hazard Index |
| HIA | Health Impact Assessment |
| Highest-HAP Product Recipe | Highest-Hazardous Air Pollutant Product Recipe |
| High-Frequency EM Sounding | High-Frequency Electromagnetic Sounding |
| HIST | Nistamine |
| HIV | Human Immunodeficiency Virus |
| HLDT | Heavy Light-Duty Truck |
| HLRW | High-Level Radioactive Waste |
| HMA | Hot Mix Asphalt |
| HMIWI | Hospital/Medical/Infectious Waste Incinerator |
| HMIWI Operator | Hospital/Medical/Infectious Waste Incinerator Operator |
| HMIWI Unit | Hospital/Medical/Infectious Waste Incinerator Unit |
| HMTA | Hazardous Materials Transportation Act |
| HNE | 4-Hydroxynonenal |
| HNO3 | nitric acid |
| HOCs | Halogenated Organic Compounds |
| HPC | Heterotrophic Plate Count |
| HPLC | High Performance Liquid Chromatography |
| HPV | High Priority Violation |
| HPV Chemical | High Production Volume Chemical |
| HQ | Hazard Quotient |
| HRS | Hazard Ranking System |
| HRS Score | Hazard Ranking System Score |
| HRSG Unit | Heat Recovery Steam Generating Unit |
| HRT | Hydraulic Retention Time |
| HSD | Home Satellite Dish |
| HSP | Heat Shock Proteins |
| HSRC | Hazardous Substance Research Centers |
| HSRL | High Spectral Resolution Lidar |
| HSRRO | Reviewing Official |
| HSS Process | Horizontal Stud Soderberg Process |
| HSWA | Hazardous and Solid Waste Amendments of 1984 |
| HTGC/MS | High Temperature Gas Chromatography/Mass Spectrometry |
| HTH | High Test Hypochlorite |
| HTML | Hyper-Text Mark-Up Language; HyperText Markup Language |
| HTS | High-Throughput Screening; High-Throughput Systems |
| HTS Cable | Very Low Impedance Cable |
| HTT | High Throughput Toxicology |
| HUC | Hydrologic Unit Code |
| HUC12 | Hydrologic Unit Code 12 |
| HUC-12 Code | Hydrologic Unit Code-12 Code |
| HUCs | USGS Hydrologic Units |
| HVA | Hazard Vulnerability Analysis |
| HVAC | Heating, Ventilation, and Air Conditioning system |
| HVAC Product | Heating, Ventilation, and Air Conditioning Product |
| HVAC system | Heating, Ventilation, and Air Conditioning system |
| HVAF | High Velocity Air Filter |
| HVLC Collection System | High Volume Low Concentration Collection System |
| HVLP Spray Equipment | High Volume Low Pressure Spray Equipment |
| HVLP spray guns | High-Volume Low-Pressure spray guns |
| HVOC | High-Volatility Organic Compound |
| H/W | Hardware |
| HW | Hazardous Waste |
| HWI | Hazardous Waste Incinerator |
| HWM | Hazardous Waste Management |
| HWM Facility | Hazardous Waste Management Facility |
| HWMU | Hazardous Waste Management Unit |
| HWS | Woodsmoke |
| Hydrogen Halides and Halogen HAP | Hydrogen Halides and Halogen Hazardous Air Pollutant |
| HYE | healthy-years equivalents |
| Hz | Hertz |