6 UNITED NATIONS STANDARD MINIMUM RULES FOR THE TREATMENT OF PRISONERS being paid to climatic conditions and particularly to cubic content of air, minimum floor space, lighting, heating and ventilation. Rule 14 In all places where prisoners are required to live or work: (a) The windows shall be large enough to enable the prisoners to read or work by natural light and shall be so constructed that they can allow the entrance of fresh air whether or not there is artificial ventilation; (b) Artificial light shall be provided sufficient for the prisoners to read or work without injury to eyesight. Rule 15 The sanitary installations shall be adequate to enable every prisoner to comply with the needs of nature when necessary and in a clean and decent manner. Rule 16 Adequate bathing and shower installations shall be provided so that every prisoner can, and may be required to, have a bath or shower, at a temperature suitable to the climate, as frequently as necessary for general hygiene according to season and geographical region, but at least once a week in a temperate climate. Rule 17 All parts of a prison regularly used by prisoners shall be properly maintained and kept scrupulously clean at all times. Personal hygiene Rule 18 1. Prisoners shall be required to keep their persons clean, and to this end they shall be provided with water and with such toilet articles as are necessary for health and cleanliness. 2. In order that prisoners may maintain a good appearance compatible with their self-respect, facilities shall be provided for the proper care of the hair and beard, and men shall be able to shave regularly.