hF

Hydrofluoric acid (HF) is a highly corrosive, toxic chemical used in glass etching, metal cleaning, and electronics manufacturing. It is a weak acid that can penetrate skin and tissue, potentially causing deep burns and systemic toxicity by binding calcium and other minerals. Exposure may require prompt medical evaluation even if skin damage seems minor. Handling and storage are subject to strict safety regulations to prevent serious injury.

High frequency (HF) refers to the radio frequency band from 3 to 30 MHz. This range enables long-range, long-distance communications through ionospheric reflection, known as skywave propagation. HF is used by amateur radio, some commercial and military services, and maritime and aviation communications, particularly when satellites or VHF/UHF links are unavailable. Its performance depends on solar activity, time of day, and atmospheric conditions, and it requires specially tuned antennas and transceivers.

Heart failure (HF) is a condition in which the heart is unable to pump blood effectively to meet the body's needs. It can result from weakened heart muscle, stiffening, or valve problems. Symptoms include shortness of breath, fatigue, swelling, and reduced exercise tolerance. Diagnosis involves imaging, blood tests, and functional assessment. Treatment typically combines lifestyle changes, medications, devices such as pacemakers or defibrillators, and, in some cases, advanced therapies or transplant.

Human factors (HF) is a discipline focused on designing systems, products, and processes that align with human abilities and limitations. It seeks to improve safety, reliability, usability, and performance by studying perception, cognition, and interaction with tools and environments. Applications span aviation, healthcare, consumer electronics, and industrial design, often integrating with engineering, psychology, and ergonomics.