Fixed Wireless Technology

Building a Tower, Part 3: Construction and Safety

In part 3 of this series, we examine the critical issues of construction and safety.

by Alex Goldman ISP-Planet Managing Editor [February 3, 2009]

Tower climbers die every year.

Elkhart, Ind.-based MapleNet Wireless sends people up towers during most weeks each year. A key part of the business is a relentless focus on safety. Not every WISP needs to have certified instructors on staff, but MapleNet, because its business focuses on building and maintaining towers, does.

In many cases, people die in part because they work on a tower alone. Nobody should ever be alone while climbing a tower. Every employee at MapleNet is certified, and no certified tower climber would ever go up without someone on the ground to ensure their safety.

In fact, every new employee is taught to the level of basic competence, says Crusie. With that certification, they are only allowed to climb certain structures and never allowed to disconnect from the safety cables.

Every employee is recertified annually on tower rescues, and the recertification requires a practice rescue 60 feet up a tower.

Crusie says that some WISPs believe that a basic tower climbing harness is sufficient, but it is not. Climbers need a full body harness. "A body harness allows you to sit. It has more rings for equipment, and alligator clips that allow the climber to be attached to the tower at all times," he explains.

It also is connected to a device called a truck that acts like a brake. If the tower climber is ever below the truck, the truck clamps on the rope, preventing it from moving and stopping the fall.

As noted in parts 1 and 2, monopole towers are particularly difficult to work on and require a higher level of certification. Reading this or any article cannot prepare you for climbing a tower. Instead, you will need training from a recognized training company like Monroe, Wisc.-based Comtrain USA or from an instructor certified by such a company.

WISPs I've spoken to don't believe that it pays to have a certified instructor on staff, and prefer to pay Comtrain for training, but if you build 40 towers or more each year, as MapleNet does, then having a certified instructor on staff makes sense.

Foundation
Every tower has a concrete foundation. The size of the foundation is specified in the design (see part 2) and depends on the size of the tower, its load, the soil you're building on, and anticipated weather.

Before every dig, MapleNet Wireless checks in with the local utility locator service to make sure that it won't cut fiber, gas, or other vital services.

Laying the foundation is not just pouring concrete. The company owns its own excavation equipment, but Crusie says that it's often more efficient to pay a local contractor to dig the hole. If the site is close enough to the MapleNet, the company will drive its equipment to the site.

Crusie adds that he has stopped subcontracting out the pouring of the concrete because it's skilled work. "The typical tower foundation is 14 feet square and 4.5 feet deep. At the bottom of the foundation is a steel rebar cage with 40 to 44 pieces of rebar per layer. Above the cage [for a three legged tower] are three piers where the legs go. The anchor bolts alone can weigh 100 pounds. Each leg of a tower has four or more anchor bolts."

"The rebar cage adds 2,000 linear feet of rebar," adds Carendar.

The concrete has to be poured so that the piers are perfectly aligned for the tower. Once the concrete is poured, it's quite solid. MapleNet has never had to jackhammer a foundation and re-pour the concrete, but that's what it would have to do if the piers ended up misaligned after the concrete hardened.

The foundation can take a week or more to dry. Putting all the metal in place requires cranes, and those cranes can also be used to hold the piers and other metal components in place. "The standard practice is to build a frame out of tower sections over the hole with winches to hold the template in place," says Crusie.

The company puts a heated blanket over the foundation to make it dry faster. The search term "concrete heated blankets" yielded 321,000 results at press time. A blanket may weigh only 55 pounds and cover 1,000 square feet. The key is to prevent cracking and freezing as well as to make the cement dry faster.

While pouring, the company also prepares for a slump test. Six cylinders are filled with concrete and subjected to the same drying conditions as the foundation. They are tested for oxygen against specifications provided by the tower manufacturer, and they are subjected to a break test in which the sections are crushed until they break and the weight at which they broke is compared to specifications provided by the tower manufacturer.

"It's never been a problem for us," says Crusie. The cement mixture would only be bad under extreme conditions, such as very humid conditions or at high altitudes. Crusie says he's heard a story of one mixture that went bad in a particularly humid area of the South.

Finishing the tower
Erecting the tower is (relatively) easy, with instructions provided by the manufacturer and with experience with similar towers, this is an area in which the company anticipates no problems.

Similarly, installing equipment, mounts, and cabling takes time and requires attention but is relatively straightforward, as it building cabinets or enclosures and fencing.

Finally, the company clears up any mess, landscaping any grass or soil torn up during the process.

Conclusion
The point of this three part series is this: towers are complex and dangerous. There are rules about how to build them and whom to notify. Many WISPs are ignoring the rules, a business decision to skirt the law because compliance is so expensive. Because safety is involved, and potential liability so high, ISP-Planet recommends compliance.

If you do choose to comply with the law, you will find that the rules help you build safe towers and maintain them safely. Build them safe and climb them safely and you'll avoid some very very serious consequences, such as death.

You could say that the rules can give your business a solid foundation.

—End