Inspection and maintenance have always been an important part of the City's management of its sewers. Modern technology has made it easier and safer to detect and fix problems without risking workers' health or lives. Regulations for sewer inspectors and other persons engaged in sewerage work, an employee handout from 1908, recommends the following: "No manhole or sewer is safe to enter in which a lighted candle will not burn brightly, and in such cases fresh air must be admitted into the sewer until a steady light is obtained. All manholes or sewers must be tested in this way before any person can be permitted to enter, except that a light must not be used where there is any indication of illuminating gas in the sewer." Today, gas detectors have replaced candles, and video cameras have partly replaced the need for human "sewer crawlers" to enter sewers.