There is another aspect of the subject which deals particularly with the safety of the light-source or method of lighting.  As each innovation in lighting appeared during the past century there immediately arose the question of safety.  The fire-hazard of open flames received attention in early days, and when gas-lighting appeared it was condemned as a poison and an explosive.  Mineral-oil lamps introduced the danger of explosions of the vapors produced by evaporation.  When electric lighting appeared it was investigated thoroughly.  The result of all this has been an effort to make lamps and methods safe.  Insurance companies have the relative safety of these systems established to their satisfaction and to-day little fire-hazard is attached to the present modes of general lighting if proper precautions have been taken.

When electric lighting was first introduced the public looked upon electricity as dangerous and naturally many questions pertaining to hazards arose.  The distribution of electricity has been so highly perfected that little is heard of the hazards which were so magnified in the early years.  Data gathered between 1884 and 1889 showed that about 13,000 fires took place in a certain district.  Of these, 42 were attributed to electric wires; 22 times as many to breakage and explosion of kerosene lamps; and ten times as many through carelessness with matches.  These figures cannot be taken at their face value because of the absence of data showing the relative amount of electric and kerosene lighting; nevertheless they are interesting because they represent the early period.

There are industries where unusual care must be exercised in regard to the lighting.  In certain chemical industries no lamps are used excepting the incandescent lamp and this is enclosed in an air-tight glass globe.  Even a public-service gas company cautions its employees and patrons thus:  “Do not look for a gas-leak with a naked light!  Use electric light.” The coal-mine offers an interesting example of the precautions necessary because the same type of problems are found in it as in industries in general, with the additional difficulties attending the presence or possible presence of explosive gas.  The surroundings in a coal-mine reflect a small percentage of the light, so that much light is wasted unless the walls are whitewashed.  This is a practical method for increasing safety in coal-mines.  However, the most dangerous feature is the light-source itself.  According to the Bureau of Mines during the years 1916 and 1917 about 60 per cent. of the fatalities due to gas and coal-dust explosions were directly traceable to the use of defective safety lamps and to open flames.