Warehouse and superstores have become wildly popular because customers love the low prices, and that they can buy everything from lumber to light bulbs under one roof.
But critics say shopping at stores like Home Depot and Wal-Mart can be dangerous. Heavy merchandise is often stacked high into the air and at Home Depot, forklifts operating during store hours can be hazardous to shoppers.
The safety issue came into sharp focus last year, after three people died at Home Depot stores in an eight-month period.
In November 1999, Rebecca Hamilton and her 79-year-old mother, Mary Penturff, were shopping at a Home Depot in Los Angeles, when a 19-year-old forklift operator knocked a heavy box from an upper shelf. The box struck and killed Penturff.
"I saw this huge pallet falling," Hamilton remembers. "It hit her on the head and there was blood pouring out of her."
Home Depot settled a lawsuit brought by Penturff's family members, who were shocked that their mother could be killed while shopping.
"I thought it was a freak accident and that something like this should never have happened," says Hamilton's sister, Maggie.
But Penturff is not the only victim of such accidents. Just six months later, at a Home Depot in Twin Falls, Idaho, 3-year-old Janessa Horner was knocked to the floor and crushed to death when a load of kitchen counter tops fell from a forklift.
Then last July, a pile of landscaping timbers fell on Jeffrey Mead and killed him at a Home Depot in Danbury, Conn.
Home Depot stores are not the only stores where there have been deadly accidents caused by falling merchandise.
In 1997, at a Wal-Mart in Virginia Beach, Va., a television cabinet killed a 2-year-old girl when it fell on her. At an Abilene, Texas, Sam's Club, a subsidiary of Wal-Mart, a 3-year-old boy died when a bookcase fell on him in 1996. And in 1994 at a HomeBase store in Edmonds, Wash., a woman was crushed to death by a load of ceramic tile.
Home Depot executive Mark Baker says his store has taken measures to ensure such accidents do not recur. "All of us feel very badly," Baker says. "We want to take away each one of those [incidents] ... and make sure it never happens again."
Last December, soon after the deaths at Home Depot, the company appointed John Mullen vice president of safety, with more than 100 new safety managers reporting to him. He tells 20/20 that among other precautions, the store cordons off aisles in which lifts are operating.
But hidden-camera footage taken by 20/20 and WABC-TV at several Home Depots show that the store's precautionary measures are sometimes neglected. Aisles are not always closed off and customers frequently walk dangerously close to busy forklifts.
One video shows customers having to duck underneath a forklift. Other video shows a forklift with a huge load of plywood coming so close to shoppers that the driver has to yell out a warning.
Safety consultant John Mrosczcyk points out other potential hazards on the tapes: Restraining bars meant to hold lumber in place are unused and left dangling, ladders and doors lean against aisles with nothing preventing them from toppling over onto customers, and heavy merchandise was found hanging over the edge of lofty shelves.
Court documents from a suit filed against Wal-Mart reveal that the store had more than 17,000 falling-merchandise incidents between 1989 and 1994. Records from a lawsuit against Home Depot show that a few years ago that store received 185 injury claims per week, though most, they say, were minor.
Home Depot's Baker says the statistics can be misleading but admits the hidden camera video shows room for improvement. He says the company wants to focus on improvements to "ever improve our shopping experience for our customer."
The company says it's committed to re-training employees as necessary, limiting what products can be stored on upper shelves, using more plastic shrink wrapping to keep merchandise from shifting, and reducing the use of lift equipment during peak store hours.
In a letter to 20/20, Wal-Mart says it, too, has learned from the tragedies in its stores and has taken measures to make sure merchandise doesn't fall from their shelves and displays. Nevertheless, safety experts recommend that shoppers stay aware of their surroundings.