The Environmental Protection Agency (EPA) defines hazardous waste as being any material with properties that could be harmful to humans or the environment. Hazardous waste comes in many forms, ranging from liquids and gases to sludges and solids. Some hazardous wastes are considered more dangerous than others. Hazardous waste management and having a waste analysis plan in action became more standardized procedurally in the United States in the mid-twentieth century, as industrial companies began to become more environmentally conscious about their actions.