Preventing Falls in Bridge Construction
Horizontal lifelines are one of the most complex types of fall protection equipment.
- By Charley Bryant
- Mar 01, 2005
IN bridge-building environments where natural foot-level anchorage points exist, contractors and inspectors can look at installing horizontal lifeline systems for their means of fall protection. Temporary horizontal lifeline systems are mostly used in bridge construction or repair. Permanent horizontal lifeline systems are mostly installed underneath large bridges for inspection and some maintenance.
Bridge workers know that a professional-grade fall protection harness and some form of lanyard or lifeline anchored to the work surface are the essential components of a fall protection setup, but projects covering large horizontal areas bring their own fall protection challenges.
Workers performing bridge repair need to have access to safe anchorage points that reduce the risk for a fall. Failure to provide some form of tie-off system could result in a fall and potentially costly health and safety litigation, or the closing down of the work site. Whenever workers are in environments where natural overhead or foot-level anchorage points exist, as in bridge work, contractors and inspectors can look at installing a temporary or permanent horizontal system.
Although installing a horizontal lifeline may appear to be as simple as stringing a line between two supports, determining the loads applied to the anchorages and the clearance required below the working surface in the event of a fall can be extremely complicated. In this respect, horizontal lifelines are one of the most complex types of fall protection equipment; therefore, pre-engineered systems by reputable manufacturers are the safest choice.
The decision to install either a temporary or permanent horizontal fall-protection system at a site can be based on two criteria: budget and project duration. For one-off projects and jobs where few workers are involved, it is more sensible to look for a temporary system consisting of sturdy but removable anchorage points and stanchions, cable, terminations, and a tensioner. For structures or applications that require ongoing maintenance or periodic inspections, permanent systems are the way to go.
What to Look For in a Temporary System
There are four essential components of a temporary system: the cable that stretches the length of the work site and provides continuous tie-off protection, the stanchions the cable is attached to, the cable terminations, and an in-line shock absorber. It is also essential that all of the above are designed as part of a complete engineered system maintaining at least a two-to-one safety factor that is required by OSHA. This means all components of the system must be rated for double the potential load that could be applied in the event of a fall. When selecting a system, safety managers should look for the following specifications:
Cable: Should be galvanized or stainless steel for corrosion resistance and be 3/8 inch in diameter or larger to ensure sufficient strength. Depending upon your work site's specific fall clearance requirements, this size of cable will allow longer spans between intermediates than smaller diameter cable, for additional work site flexibility.
Stanchions: Must offer a compatible connection to the walking/working surface to provide a positive and safe anchor point for the cable lifeline system. They must be robust enough to ensure they are capable of withstanding a two-to-one safety factor based on the potential horizontal forces and be at least 42 inches high to minimize free fall distances. Bypassable stanchions should be used for intermediate supports to guarantee 100 percent fall protection.
Terminations: Must be chosen based on the specific size of cable being used. They must be capable of withstanding a two-to-one safety factor based on the potential horizontal fall arrest forces.
In-line shock absorbers: These devices offer the ability to control the horizontal forces created in a fall situation. Manufacturers of these products offer specific loading requirements based on system performance. Knowing what your end-anchor forces are ahead of time makes it easier to install an OSHA-compliant system that maintains a two-to-one safety factor. Keep in mind the use of in-line shock absorbers also increases the fall clearance necessary to safely stop a fallen worker.
What to Look For in a Permanent System
There are four essential components of a permanent system: the cable that stretches the length of the work site and provides continuous tie-off protection, the sleeve that travels along the cable, intermediate brackets that provide support for the cable, and cable terminations. When selecting a system, safety managers should look for the following specifications:
Cable: There are two basic cable sizes: one 12 mm, the other 8 mm. Depending on which applications the systems are being used for, 12 millimeter-diameter, stainless steel cables are preferable, with a strength exceeding 18,000 pounds. These allow span distances of up to 100 feet and up to six users on the cable at any one time. The 8 mm systems are used for lighter duty work with a strength exceeding 8,000 pounds and accommodating a maximum of two users.
Sleeve: Sleeves vary greatly, but higher-end models should feature rollers to assist movement along the cable and should offer hands-free operation when bypassing all intermediate brackets on the cable.
Intermediate brackets: These brackets provide stability in the overall system. Additional protection is provided when brackets can swivel on the anchoring bolt and deform in the event of a fall, helping to dissipate the energy generated and minimize the load or force imposed on the worker.
Terminations: These can have tensioners and in-line shock absorbers built into them. Look for terminations that offer the same breaking strength characteristics as the cable. Swageless terminations also can be used with less tooling needed for installation.
Other elements of a permanent system, such as corner brackets, can help with mobility in more complex and non-linear system setups. In-line shock absorbers also can be added to minimize forces on the end anchors.
In addition to using a temporary or permanent system, bridge workers should considering using nets as additional passive fall protection. Not only can nets be used for fall protection, they can also be used for catching debris below a work site, which is an important detail bridge workers should take into account when working at a height where common hazards can include the traffic below.
Users' Equipment
Both temporary and permanent horizontal lifeline systems require user equipment such as a full body harness, shock-absorbing lanyard, or anti-ratcheting self retracting lifeline. This equipment must be OSHA compliant and offer arresting forces of 900 pounds or less. It also should be easy to use and comfortable to wear, providing added worker satisfaction and productivity.
To help choose the right fall protection equipment, there are four basic steps in mind:
1) Assess the hazard. What kind of work are you doing, and where are your fall hazards located? Different stages of the bridge construction may require different forms of fall protection.
2) What will happen in the case of a fall? Think about the structures below you and your fall clearance.
3) Select the appropriate equipment for the job. Think about the level of comfort and mobility you need from your equipment and the location of your work.
4) Seek training. When using safety products, even the smallest things make a very big difference. You should be trained in the most effective and quickest ways to make adjustments to a harness, to spot potential problems with equipment, and to rectify a bad situation if anything goes wrong.
Installation and Training
Pre-engineered temporary horizontal lifeline systems should be installed by qualified or competent personnel as defined by OSHA. A typical installation of a permanent system can take several months, from an initial site survey and detailed assessment of a client company's needs to hardware installation and on-site training.
One source of assistance is fall protection manufacturers, who offer pre-packaged temporary systems and can perform site-specific assessments. Always refer to the manufacturer's user instructions for complete details on the design, installation, use, and maintenance of any fall protection system.
This article appeared in the March 2005 issue of Occupational Health & Safety.
This article originally appeared in the March 2005 issue of Occupational Health & Safety.