Working conditions in the early part of the 20th century were dirty, crowded, and dangerous. Factory jobs were booming, and more families were moving to the cities to find opportunities. Also during the time is when there was a influx of immigrants coming from Italy and Ireland to work in the cities. Factory jobs were low paying, dirty, and unethical. This is the time when children were working just as long days as their parents and also put into dangerous situations where many times they would become injured at work. After the 1920's the government finally realized it needed to get involved and provide a law based on fair and just working conditions for all.
A universal answer might be taken from my own trade which was sanctioned in Ohio in 1900. One issue that has never changed is weather exposure with insufficient outerware, gloves; "street shoes" or cumbersome rubber "galoshes" that picked up every ounce of mud or snow underfoot. Lunch would have been cold sandwiches as today and a 1920's thermos wouldn't have kept anything warm an hour after arriving. Many europeans, even to the time I began in the '70's, brought bottles of beer in their lunchsack and many guys "drank their lunch." On large construction jobs there would have been everpresent smoke from burn-barrels and trash; fumes from equipment; boiling tar; coal smoke from boilers. Tools were heavy, cumbersome and required immense maintenance. On some jobs, horses and mules were still used so you can imagine what that added. Journeymen brought age old skills to America along with the culture of the indentured apprentice, who in England and Germany often lived in the journeyman's home under servant conditions. In America, apprentices are still indentured and depending on the trade (like plumbers and steamfitters) can spend five years in training, mostly at night after the workday. New materials and equip. have made work easier but the nature of manual work's toll on the body is as tough today as it always was.