One significant event that has accelerated "greening" in the corrections field is the 2012 publishing of the "Greening Corrections Technology Guidebook" by the National Law Enforcement and Corrections Technology Center System. Currently, most states have launched recycling programs, and correctional facilities have installed alternate or transitional energy programs, such as the use of solar panels and vehicles powered by natural gas. The Sustainability Oriented and Environmentally Responsible Practice in Corrections Committee is the largest active national committee of the American Correctional Association. Cost savings underlie some of the urgency of lighting upgrades, recycling trash, materials flow, the reduction of toxics, composters, and food dehydration to reduce pulp waste. At least six states now invest in combined water purification, fish farming, and vegetable growing in the same facility. Some states are requiring the use of inmate workers in some of these "greening" efforts, which carries with it a job training component; for example, one Ohio facility did a large thermal installation with inmate crews, and the contractor was so impressed with the work of some of the inmates that he issued formal job offers the inmates could present to the parole board. One model being used is the "energy savings performance contract" (ESPC). Under this model, an energy services company (ESCO) covers the upfront cost to achieve energy savings at a property or portfolio of properties as a service. This model guarantees savings for a set time period in exchange for payment from the energy cost savings.