Except in technical education and career schools or in public schools teaching manual training, no child under sixteen years of age shall be employed or permitted to work in adjusting or assisting in adjusting any belt upon any machine, or in oiling or assisting in oiling, wiping or cleaning machinery, while power is attached, or in preparing any composition in which dangerous acids are used, or in soldering, or in the manufacture or packing of paints, dry colors or red or white lead, or in the manufacture, packing or storing of gun or blasting powder, dynamite, nitroglycerine compounds, safety fuses in the raw or unvarnished state, electric fuses for blasting purposes or any other explosive, or in the manufacture or use of any dangerous or poisonous gas or dye, or composition of lye in which the quantity thereof is injurious to health, or upon any scaffolding, or in any heavy work in any building trade or in any tunnel, mine or quarry, or in operating or assisting to operate any emery, stone or buffing wheel; and, except as otherwise provided in subsection (b) of section 31-23, no child under sixteen years of age shall be employed or permitted to work in any capacity requiring such child to stand continuously.