Rigging Throughout History: The Hoover Dam

The Hoover Dam (originally known as the Boulder Dam) is one of American’s most famous landmarks—An engineering marvel of it’s time, that still remains one of the largest and most impressive dams to ever be created.

When the construction of the Hoover Dam was complete in March of 1936, it was the heaviest and tallest dam to exist, surpassing the next in line, The Arrowrock Dam, by double the height and triple the width.

This is impressive in any decade, right? Absolutely! But before we had the technology we have today that makes huge construction projects like these much easier, and more importantly, much safer, this feat was even more notable.

Read on to find out how, and why!

The Hoover Dam: It Begins

hoover dam inspection party 1931
An inspection party near the proposed site of the dam in the Black Canyon on the Colorado River.

The Hoover Dam was created to solve two different problems. If you’re not familiar, the Hoover Dam is located on the border of Nevada and Arizona, in the Black Canyon of the Colorado River. Prior to construction in 1931, the Colorado River would flood every spring, and often destroyed villages and crops along its path. This was one reason to create the dam, because water would be more controlled and displaced in calculated locations. Then, of course, the second reason is why most things get created—Income generation.

How does the Hoover Dam work? As water flows through large pipes inside the dam, turbines rotate, which then spins a series of magnets, past copper coils and a generator to produce electricity. This electricity helps support Nevada, California, and Arizona still, to this day!

As we mentioned before, this was not (and still isn’t) a simple task. Even today this wouldn’t be a construction project to scoff at, so you can imagine how difficult it was in 1931.

The Hoover Dam is 726.4 feet tall from the foundation of rock at the bottom to the roadway that runs along the top, and is constructed from 3.4 Million cubic meters of concrete. And if that’s not daunting enough, it was constructed in the middle of the desert, which at the time had no local workforce, no infrastructure, or transportation. The closest access to civilization was 30 miles away in Las Vegas, which had a railroad. This railroad became their one and only access point to bring in workers, materials, and supplies.

The construction of the Hoover Dam happened in the middle of the great depression, so despite it being in the middle of nowhere, it didn’t take long to get the workforce they needed. Within 3 weeks of the project being announced, the closest employment office in Las Vegas had received 12,000 applications for work. This wasn’t going to be easy work, but it was a stable income—Something many people at the time didn’t have.

black and white frank crowe hoover dam engineer
Frank Crowe.

Unfortunately, this made exploiting workers easy—If a worker wasn’t able or comfortable doing a task, they would simply be sent away and replaced with one of thousands of other men who’d happily step into the job.

An engineer named Frank Crowe was in the charge of the project, and had 7 years to complete it. If the project wasn’t complete within this timeline, there would be an approximate $3,000 a day financial penalty. Crowe was prepared to complete the project by any means necessary, and even earned the nickname ‘Hurry-Up Crowe’ for his constant efforts to ensure the project was unfolding on-time and on-budget.

A rushed project focused on speed above all else, is often not a safe project—And the Hoover Dam is a perfect example of this.

The Hoover Dam: Phase One

Allow me to set the scene for you—Thousands of untrained workers, in the middle of the desert, during one of the hottest summers on record (temperatures peaking at 49°C), faced with the monumental task of diverting one of America’s most powerful, dominating and unpredictable rivers—Sounds like a perfect storm…right?

In order to create a construction site in the riverbed, four diversion tunnels were driven through the canyon walls, two on the Nevada side and two on the Arizona side. These tunnels were 56 ft (17 m) in diameter and had a combined length of nearly 16,000 ft, or more than 3 miles (5 km). They also had to be sturdy enough to handle the powerful Colorado river, which meant about 850-cubic metrics of water a second.

The process of creating these tunnels involved  drilling holes into the rock, then packing the holes with dynamite. In 1931, this work was traditionally very slow and tedious, with each hole being drilled out individually with a simple drill or jackhammer. But, with a tight deadline in mind, Frank Crowe came up with a faster solution. Specialized 10-ton trucks were brought in that would each have 50 men on board, running 24-30 drills at one time. These trucks would be backed up along the walls of the tunnel, and half of the wall would be able to be drilled at a time. With 8 of these trucks and 500 drills, they were able to create the tunnels in record time. and 10 months ahead of schedule.

But, this did not come without consequence. Temperatures within the tunnels could reach upwards of 60°C, and the only solution presented for this was a team of people they called the “ice brigades” who would go into the tunnels to bring out exhausted workers to plunge them into ice water. Fourteen men died of heat exhaustion alone during the construction of the tunnels.

And the hazards don’t stop there – Many other workers were hospitalized or killed due to carbon monoxide poisoning because the tunnels didn’t have the proper ventilation to support the steady stream of trucks going in and out. Many of these deaths were reported as a pneumonia outbreak, according to doctors at the time, but it’s widely believed that it was misrepresented by the construction company to avoid paying death compensation.

The Hoover Dam: Phase 2

hoover dam high scaler 1931
One of the Hoover Dam “High Scalers”.

After the tunnels were complete, cofferdams (small enclosures so the water can drain) made from materials extracted from the tunnels were put in place, and water was drained from the construction site. In order for the dam to rest on solid rock, accumulated erosion soils and other loose materials in the riverbed had to be removed. Since the dam is an arch-gravity type, the side-walls of the canyon bear weight from the dam as well, so the side-walls also had to be excavated.

The team that performed these side-wall excavations was called “high scalers” and they would work suspended from the top of the canyon with ropes (NOT proper fall protection equipment) and would climb down the canyon walls removing any loose rock with jackhammers and dynamite. Falling objects were the number one cause of death on the dam site, with high scalers often being the victims of this hazard.

To protect themselves against falling objects, some high scalers took cloth hats and dipped them in tar, allowing them to harden. When workers wearing such headgear were struck hard enough to inflict broken jaws, they sustained no skull damage.

These hats went on to be called “hard boiled hats” and companies began ordering the hats and encouraging their use—One of the first versions of the modern hard hat (but not NEARLY as safe, so don’t get any ideas about dipping old hats in tar…please, buy a certified hard hat!)

The Hoover Dam: Phase 3

Once excavations were complete, the concrete staring pouring in, 6,600,000 tons of it to be exact. You may notice a squared pattern along the side of the Hoover Dam, and that’s because it’s made of a series of blocks of concrete—Not a large pour. This is because if they attempted to pour out the Hoover Dam in one continuous piece, it would still be drying today!

LEFT, A bucket holding 18 tons of concrete is maneuvered into positions. RIGHT, Concrete lowered into place.

When the ingredients of concrete are combined (cement, aggregate & water), they trigger a chemical reaction. This reaction generates internal heat, and slows down the curing process—The larger the pour, the longer it takes to harden. A series of interlocking blocks allows the concrete to harden in a more reasonable time-frame.

But there was also the opposite problem—Liquid concrete could harden too fast when attempting to transport it to the top of the dam, where the blocks were being formed, because of the intense desert heat.

To solve this problem, Frank Crowe designed an elaborate network of overhead cables and pullies that would move across the construction site carrying buckets of concrete. This was one of the largest rigging systems to ever be used on a construction site at the time! But I think it’s safe to say it probably wouldn’t pass a modern inspection (definitely not from our LEEA certified technicians)—So don’t start taking any notes!

The Hoover Dam: Lessons Learned

The Hoover Dam project was complete in 1936, 2 years quicker then the original timeline suggests. During construction, 112 people died.

Back in 1931, it wasn’t that uncommon to have a high fatality rate on construction sites. Some of that was because they didn’t have access to the technology we have today (or at least not as good quality), like fall protection equipment or modern hard hats, and other personal protective equipment (PPU). Some of it was also due to the fact that employers were not held accountable to ensure they weren’t putting their workers into unsafe working conditions – Like using the proper equipment and ensuring it’s been inspected and in full working order.

Construction is a dangerous industry, even today, but that doesn’t mean we should ever accept fatalities or even injuries. It’s not 1931 anymore—Employers and construction workers have the responsibility and the right to be able to perform their jobs safely. Now we DO have access to the proper means necessary to create a safe work environment, so there’s no excuse not to be using them.


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