| β | Beta Particle |
| BA | Bacillus anthracis |
| BAC | Bacterial Artificial Chromosome |
| BACM | Best Available Control Measures |
| bact | Best Available Control Technology |
| BAF | Bioaccumulation Factor |
| BaP | Benzo(a)Pyrene |
| BART | Best Available Retrofit Technology |
| BAS | Building Automation System |
| Baseline BAT Limitation | Baseline Best Available Technology Limitation |
| Baseline BCF | Baseline Bioconcentration Factor |
| BASINS | Better Assessment Science Integrating |
| BAT | Best Available Technology (regulatory) |
| Batch HMIWI | Batch Hospital/Medical/Infectious Waste Incinerator |
| Batch-RIN | Batch Renewable Identification Number |
| batea | Best Available Technology Economically Achievable |
| BB | Broadband |
| BBB | Blood-Brain Barrier |
| BBD | Black-Band Disease |
| BBDR Model | Biologically Based Dose Response Model |
| bbl | Barrel; Benthic Boundary Layer |
| BBP | Butyl Benzyl Phthalate |
| BCA | benefit-cost analysis |
| BCAA | Bromochloroacetic Acid |
| BCC | Bioaccumulative Chemical of Concern |
| BCF | Bioconcentration Factor |
| BChl | Bacteriochlorophyll |
| BCOP | Bovine Corneal Opacity and Permeability Assay |
| BCR | Biochemical Reactor |
| BCT | Best Control Technology; Best Conventional Pollutant Control Technology |
| BDAT | Best Demonstrated Available Technology |
| BDCM | Bromodichloromethane |
| Benchmark RFP Plan | Benchmark Reasonable Further Progress Plan |
| BER | Base Excision Repair |
| BES Emergency | Bulk Electric System Emergency |
| BFCC | Basic Format/Content Checker |
| BFT | Baffled Flask Test |
| bhp | Brake Horsepower |
| BI | Background Information |
| BIC | Bayesian information criterion |
| BID | Buoyancy Induced Dispersion |
| Bioaccumulation potential factor | Hazardous Wastestream |
| Bioassessment | Biological Assessment |
| Biocriteria | Biological Criteria |
| Biogas Closed Distribution System RIN Generator | Biogas Closed Distribution System Renewable Identification Number Generator |
| Biogenic VOC | Biogenic Volatile Organic Compound |
| Biomonitoring | Biological Monitoring |
| BIOS | BIOlogical System |
| BIS | Broader in Scope |
| BLAD | Bovine Leukocyte Adhesion Deficiency |
| BLD | Below Limit of Detection |
| BLO System | Black Liquor Oxidation System |
| BLS | Black Liquor Solid |
| BMC | Benchmark Concentration |
| BMCL | Benchmark Concentration Limit |
| BMD | Benchmark Dose |
| BMD10 | Benchmark Dose 10 |
| BMDL | Benchmark Dose Limit; benchmark dose lower confidence limit |
| BMI | Body Mass Index |
| BMP | Best Management Practices |
| BMR | Basal Metabolic Rate; Benchmark Response |
| BNP | Bimetallic Nanoscale Particle |
| BNR | Biological nutrient removal |
| bod | Biochemical Oxygen Demand; Biological oxygen demand |
| BOF | Basic Oxygen Furnace |
| BOP | Blowout Preventer |
| BOP (Steel Making) | Basic Oxygen Process |
| BOPF | Basic Oxygen Process Furnace |
| BOX-PCR | Repetitive Polymerase Chain Reaction - BOX Primers |
| BP | boiling point |
| BPA | Bisphenol A |
| BPFV | Bioaccumulation potential factor value |
| BPJ | Best Professional Judgment |
| BPT | Best Practicable Control Technology Currently Available |
| BPWTT | Best Practical Wastewater Treatment Technology |
| Bq | Becquerel |
| BRAC | Base Realignment and Closure Site |
| BrDBP | Brominated Disinfection By-Product |
| BRI | Building Related Illness |
| B-RIN | B Renewable Identification Number |
| BSAF | Biota-sediment accumulation factor |
| BSE | Bovine Spongiform Encephalopathy |
| BSO | Benzene Soluble Organics |
| Bt | Bacillus thuringiensis |
| BTEX | Benzene Toluene Ethylbenzene And Xylene |
| BTF | Biotransfer factor |
| BTM | Best Tracer Method |
| Btu | British thermal unit |
| Bulk NGL | Bulk Natural Gas Liquid |
| BUN | Blood Urea Nitrogen Measurement |
| BUR | Built-Up Roof |
| BUV | Backscatter Ultraviolet Spectrometer |
| BVD | Bovine Viral Diarrhea |