All-electronic television, first demonstrated in September 1927 in San Francisco by Philo Farnsworth , and then publicly by Farnsworth at the Franklin Institute in Philadelphia in 1934, was rapidly overtaking mechanical television. Farnsworth's system was first used for broadcasting in 1936, reaching 400 to more than 600 lines with fast field scan rates, along with competing systems by Philco and DuMont Laboratories . In 1939, RCA paid Farnsworth $1 million for his patents after ten years of litigation, and RCA began demonstrating all-electronic television at the 1939 World's Fair in New York City . The last mechanical television broadcasts ended in 1939 at stations run by a handful of public universities in the United States.
People can be exposed to tellurium in the workplace by inhalation, ingestion, skin contact, and eye contact. The Occupational Safety and Health Administration (OSHA) limits ( permissible exposure limit ) tellurium exposure in the workplace to mg/m 3 over an eight-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set the recommended exposure limit (REL) at mg/m 3 over an eight-hour workday. In concentrations of 25 mg/m 3 , tellurium is immediately dangerous to life and health .