Before 1930, refrigerators were not only bulky and expensive but extremely dangerous. Chemicals used as refrigerants—ammonia, methyl chloride, and sulfur dioxide—were not only toxic but highly combustible. In 1929 a leak in a methyl chloride refrigeration system caused an explosion that killed more than 100 people in a Cleveland hospital. It was no wonder that consumers preferred their old iceboxes. That would all change in 1930 with the invention of Freon by a General Motors researcher.