By DAVID GODKINDemolition
Demolition experts a rare breed in construction industry
They are the gunslingers of the demolition industry. Itinerant marksmen brought into town to vanquish structures that have cast a long, dark shadow over the landscape for too long.
Even the language they use is reminiscent of the old west: “We don’t demolish buildings. We shoot ’em.”
Just like the Wyatt Earps of the old west, the names of Jim Redyke, Merritt McAlinden and Richard Gustafson are legendary. The difference is they are still standing; still doing the necessary work that is modern day explosives demolition.
Not everyone can do the job. Not everyone who needs their help gets it. That, says demolition expert Jim Redyke, is because not every structure lends itself to explosives demolition.
“First of all you’ve got to have sufficient room around it. And the storey height needs to be enough so that there’s a cost benefit. If you can take it down with a smaller machine then that’s easier for the demolition contractor. The difficulty occurs when the structure gets a little higher.”
If your high reach excavator’s not high enough, call his company, he adds.
Founded in 1975, Dykon Explosive Demolition in Tulsa, Okla. has taken on complex explosive demolition projects throughout North America, Saudi Arabia, Korea, South Africa and Aruba. Dykon has shot everything from highrise buildings, to smoke stacks and bridges, to piers, heavy steel power and boiling houses. In each case, Redyke says where you place a charge and the delay pattern as a structure implodes are critical.
Case in point: Macey’s Department Store in downtown Houston, Texas this past fall. “Sometimes you start at one end and shoot it from there,” he says. “Macey’s was 300 foot square and twelve stories high and we fired it in the middle. We did a series of circles so that the middle dropped down and all four corners fell into the middle.”
Timing is everything
But Macey’s wasn’t the biggest explosive demolition Dykon has taken on. That honour went to the coal fired Lakeview Generating Station east of Mississauga, Ont. At 1,200 feet long, the plant’s four smoke stacks – the Four Sisters – were shot on June 12, 2006. The power plant fell the following year. Here, says Redyke, the delay pattern was critical.
“To fell a structure you’re removing the support columns. And removing them with explosives sometimes on multiple floors and the timing and sequence to remove all that is based on the direction in which you want that to go.”
Each stack at the Lakeview Generating Station was designed to fall in an easterly direction, one every four seconds. Just as important was the size of the explosive material used to determine both the extent of the blast and the amount of “fly,” or extraneous material, that is likely to be ejected into the surrounding area. Figuring this out requires a test blast.
“You’ll blow a series of holes in one of the columns and then put different quantities of explosives in each hole so we can determine the minimum amount of explosives needed to take it out.”
The nature of the application determines the type of explosive used. The industry’s material of choice remains dynamite, especially in concrete demolition and large, complex applications. RDX, typically used in military demolition applications in the form of linear shaped charges (LSC), also plays a major role in construction demolition. Often dynamite and LSCs are used together – LSCs to partially cut through the supporting steel legs to weaken a tower or smokestack, for example.
“Then you strap some dynamite to the back of that piece and kick it out,” says Ron Elliott, president of International Blasting Consultants Ltd. in Coquitlam, BC. In the absence of both LSC and dynamite the supports “might jam, but not move,” he adds.
Hold the Shot! Hold the Shot!
Scott Gustafson says bridge demolition – his company Demtech Inc.’s specialty – depends almost exclusively on LSC explosives. “LSC doesn’t fragment the steel. It basically just cuts a steel member off like a cutting torch but at a speed of about five miles per second.”
In box beam bridges built of angle iron and steel vertical plate the charge is placed in the middle of a bridge’s horizontal panels rather than at the joints where gusset plate and reinforcement are more resistant to the blast.
“That said, LSC is very precise material. It has to be applied with a lot of care or you won’t really get the results you’re looking for; you might not get the severance on a beam that you need.”
Where a building under demolition will implode by design in any one of several directions a bridge typically falls in just one direction: straight down. In fact, Gustafson’s biggest problem is not direction; it’s large, heavy structures over navigable waterways and the narrow twelve-hour window that explosive demolition companies have to shoot down a bridge.
“The twelve hour window doesn’t start when you start the blast, it starts when you close the bridge off. So you’ll lose a couple of hours in the morning and that makes it really difficult.”
Another challenge is protecting surrounding structures, traffic and people. To protect crowds from concrete fly, supporting columns are wrapped in geotechnical fabric, filter cloth or multiple layers of chain link. Manufacturers are constantly looking at ways to improve these products, says Redyke.
“The geotech cloth has gotten better and better over the years. And as you learn to do this you make some other adjustments that help. For example, you also put an additional curtain around that to minimize as much of that throw as possible.”
During implosion of the Lakeview Generating Station more than a thousand bystanders were on hand for the event while media helicopters buzzed overhead. Because it was a structural steel project, the first line of defense was large heavy plywood constructed boxes wrapped in heavy conveyor belting, enclosing the charge area. The same approach is adopted when demolishing structure steel bridges. The plywood box absorbs fragmented steel “flying from the backside,” says Gustafson.
“On the other side you have the copper fragments that come off the linear shaped charge and when it explodes those LSC fragments are moving 28,000 feet per second. At close range they can do collateral damage to another bridge, utilities or fiber optics.”
Keeping people at least 1,000 feet from the blast site is your num
ber one job, says Gustafson. Prior to a blast, police, local officials, contracting personnel and Demtech staff set up safety perimeters and monitor the blast area visually and by radio. Occasionally local residents are told they must evacuate their homes because of their proximity to the blast site.
Yet sometimes even your best efforts come to naught, especially when simple human stupidity kicks in, says Gustafson. Some people just can’t resist stepping out on their porch to take “that Kodak moment” – or worse.
“In Pennsylvania years ago there was a little mom and pop grocery store set right on the end of a 13-arch concrete bridge we were demolishing. The owners posted notices telling people not to park there and somehow someone the night before had parked in the parking lot.”
Figuring he had secured the area and that the vehicle would survive Gustafson began the ten-second countdown. “The count is always a silent count at around five or six and everyone goes silent and all of a sudden I hear a guy yell, ‘Hold the shot! Hold the shot!’” At that moment, a man emerges from between two buildings and starts running down the hill towards the blast area screaming: “That’s my car, I gotta get my car!”
“One of two cops watching from a safe area nearby does a flying tackle on this guy and buries this guy’s head in behind a doghouse. The cop speaks through his mic and says, ‘I’ve got him secure. Go for the shot.’”
No half measures, please
Sometimes problems occur with the shot itself. One thing to avoid is setting too large a charge. Gustafson says you want to maintain integrity through certain parts of the building to make it collapse where and how you want it to.
Vince Alvernaz, division manager for Demolition at Pacific Blasting in Burnaby, B.C. says another real concern in the industry are charges that fail to bring an entire structure down. “Depending on where the failure in a structure occurs your only recourse may be to bring in an excavator to complete the job.”
Sometimes even this isn’t enough, adds Jim Redyke. “I shot a grain elevator once and there wasn’t enough material in the hinge to push it over and it squatted. It sat on an angle and they had to bring in a crane and a wrecking ball to take down the rest of it. So it’s not always an excavator.”
Alvernaz says one of the most unique explosive demolition jobs Pacific Blasting has ever taken on was Pacific Palisades Hotel, a triple tower complex in the heart of Vancouver that required six months of planning before the shoot could begin.
The challenge was to implode one tower without damaging the other two. This meant physically separating it from the other two so that the parkade and the complex’s glass roof swimming pool – a mere 25 feet away from the building – were protected. “We had to put impact walls through the parkade, around the structure and over the roof of the pool.” Impact walls (I-beams) filled with timbers, limited the amount of concrete fly ejected at the time of the detonation at Pacific Palisades.
Of utmost importance is the component on the other end of the blast: the detonator. Gone are the days of the plunger box, says Jim Redyke. In its place are electronic detonators with programmable computer chips.
“It really improves timing accuracy and is very useful in big jobs where a few milliseconds make the difference. Manufacturers are always looking to develop new and improved product.”
Interestingly, experts argue that outside of rock blasting very little formal schooling is available, or needed, in explosives demolition. Technical schools may provide a single chapter on explosives demolition or offer a video on the use of LSC charges.
Gustafson says students don’t get taught a whole lot about it. “Pretty much most of it is hands on.”
Jim Redyke says he was fortunate enough to work with someone knowledgeable about explosives demolition. And because so few companies are interested in this line of the demolition business, he doesn’t sees sufficient demand for formal training to warrant it.
“Now we do safety training, but basic technique no one wants to share that. What I know I wouldn’t want to teach at a school because why would I want to educate my competition?”
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