water treatment systems can be installed in containers and shipped around the world.[84] Electric generators can be permanently installed in containers to be used for portable power.[85] Repurposing[edit] Container City in Cholula, Mexico uses fifty old sea containers for 4,500 m2 (48,000 sq ft) of workshops, restaurants, galleries, etc., as well as some homes. Containers have long been used for other purposes, typically but not always at the end of their voyaging lives. US military often used their Conex containers as on-site storage, or easily transportable housing for command staff and medical clinics.[86] Nearly all of over 150,000 Conex containers shipped to Vietnam remained in country, primarily as storage or other mobile facilities.[23] Permanent or semi-permanent placement of containers for storage is common. A regular forty-foot container has about 4,000 kg (8,818 lb) of steel, which takes 8,000 kWh (28,800 MJ) of energy to melt down. Repurposing used shipping containers is increasingly a practical solution to both social and ecological problems. Shipping container architecture employs used shipping containers as the main framing of modular home designs, where the steel may be an integrated part of the design, or be camouflaged into a traditional looking home. They have also been used to make temporary shops, cafes, and computer datacenters, e.g., the Sun Modular Datacenter. Intermodal containers are not strong enough for conversion to underground bunkers without additional bracing, as the walls cannot sustain much lateral pressure and will collapse. Also, the wooden floor of many used containers could contain some fumigation residues, rendering them unsuitable as confined spaces, such as for prison cells or bunkers. Cleaning or replacing the wood floor can make these used containers habitable, with proper attention to such essential issues as ventilation and insulation. See also[edit] BBC Box Container ship Containerization Customs C