A common trap that many people fall into with extension cords is plugging them in once and then never taking them out. As stated by OSHA's electrical standards, extension cords are only permitted to be used as a temporary wiring solution for a maximum of 90 days. Extension cords aren't intended or rated to be part of permanent fixtures, and using them in that way isn't considered safe. Incidentally, OSHA's regulations also prohibit "daisy chaining" extension cords and power strips, or plugging one extension cord into another to increase its range. Extension cords are not rated to be safely used in this manner, so doing so would be a violation.