Dear Vijay,
Various hazards associated with Confined space one is Electrical shock due to wet / moist surface of the said place. So, the chance of electrical shock is more in high voltage. But as voltage is lower than chance is lower for serious electrical shock.
By use of 24 Volt light the purpose of illumination is satisfied same as other volt lighting.
And apart of this as per Section 36A(a) of Factories Act, 1948 - no portable electric light or any other electric appliance of voltage exceeding twenty-four volts shall be permitted for use inside any chamber, tank, vat, pit, pipe, flue or other confined space; [ unless adequate safety devices are provided]