FALL PROTECTION & DEBRIS CONTAINMENT DURING CONSTRUCTION

by C.Warren Duncan and Ralph BennettIII, PE,ACSE

ABSTRACT
The purpose of this paper is to review the current practices in the United states for both fall protection and debris containment during high rise construction. A performance comparison will be made by comparing , in more detail, flexible and rigid passive protection structures. Furthermore, an attempt has been made to review the general approach to protection of other countries.

INTRODUCTION
Fall protection and debris containment can be broadly categorized as follows, "Fall Protection" is for the protection of the construction site staff, whereas "Debris Containment" is for the protection of the public and the few workers on the ground. These two systems are often viewed as one and the same. However, they are not, and in most cases, cannot be made to achieve the same purposes. In addition, the authorities requiring these two different types of protection are in most cases different regulator bodies whose areas of responsibility are different. Debris and personnel protection systems fall into two further categories, active or passive protection. An active protective system means that both workers and debris are actively contained from accidently falling off the structure. All workers are protected by guardrails, or secured by safety harnesses. Screens are provided around each floor to contain the debris on the floor where it is generated. Some people consider active to be where the worker is required to do something to ensure their safety. Passive protection systems consist of either a sidewalk bridge and/or horizontal nets to catch debris and/or a man falling off the structure. The passive system can be either a rigid or flexible structure, however , both must absorb dynamic loads well. REGULATIONS OSHA's "Safety and Health Standard for the Construction Industry" requires that workers be protected from onsite hazards. A recent survey by OSHA has shown that 33% of all construction fatalities are due to falls. This means that, to an increasing extent, employers are being required to review the means and methods of fall protection provided for their employees. OSHA, on the other hand, does not usually address public hazards. The local bodies who govern the district in which construction is being carried out take responsibility for the protection of the public.

FALL PROTECTION
OSHA currently requires that an employee be provided with ladders, scaffolds, catch platforms, temporary floors, safety lines and/or safety belts. If these are not practical and if the fall height exceed 25 ft, safety nets must be provided. Proposal regulations published in the Federal Register, April1990 are more stringent. These regulations read that " Employers SHALL provide a guardrail system as the primary fall protection system for all working and walking surfaces". Where this is not feasible, personnel fall protection must be provided. Guardrails must be designed to withstand the outward or downward loads of 200lbs and the midrail must withstand 150 lbs.

ACTIVE FALL PROTECTION

Active fall protection in the US generally consists of double steel cables stretched around the perimeter of each open floor of the building,one cable at 42 in. the other midway between the guardrail and the floor. The major drawback of multi-storied construction is that any handrail system has to be secured. It is obvious that the topmost level has nothing to which a handrail can be connected and the levels below generally have activities on the outside edge of the building which prevents installation, as in the case of concrete buildings where they tend to erect two to three floors at a time before laying out the decking for the floor, access to install the guardrails would be more dangerous than leaving them off. In addition, they serve little purpose because only the connectors who have no fall protection can access these areas.

PASSIVE FALL PROTECTION SYSTEM
Safety nets are probably the only viable passive fall protection system available to the industry. Installed properly, a net can arrest the fall of a person after falling a considerable distance without injury. The ANSI regulations recommend the fall distance be limited to 25 ft. Passive fall protection systems as defined By ANSI A10.11 (Personnel and Debris Nets) are used in some areas and are mandatory in NYC. They are however fairly common on bridge projects both during construction and during maintenance. In New York City, building sites must have nets installed, although they are primarily for debris. They are located no more than two floors below the stripping level in the case of concrete buildings and no more than ten levels belong the derrick on steel buildings. This necessarily means the nets will be more than 25ft below the uppermost work levels, which is the limit which ANSI recommends for personnel protection. However, those workers who have had the opportunity to use them are thankful they were there. Sidewalk bridges cannot be considered passive fall protection as the injuries sustained by a worker falling from any height would be significant. In fact, there has been instances of people falling through sidewalk bridges.

DEBRIS CONTAINMENT
Active Debris Containment With the exception of New York City and some isolated projects in cities such as Atlanta, there are no requirements for actively containing debris. New York City requires a top guardrail at 60 in, a fine 1/8 in net stretched from this cable to the floor and secured to the floor by Hilti-type attachments or equivalent. This system doubles as an active fall protection system for workers as well as containing debris within the building. Passive Debris Protection Passive protection, by definition means that the debris has fallen some distance before the system is required to arrest the fall. For the debris to be successfully contained, the device must not only be able to withstand the dynamic loading, it must be either wide enough to the point of departure for the trajectory of the object from rebuilding and causing damage. This means the system must be either close enough or extend out far enough for the debris to fall into it and not out into the street. The common way of catching debris after it has fallen from a sidewalk shed, bridge, hoarding or canopy. Most cities require them on construction sites sites where the public has access adjacent to the site. The most often used regulation is theUBC requirements which many cities have adopted. This requires a static load capacity of 150 lbs ft (light duty loading). The exception to this is in NYC where they require 300lbs/ft (heavy duty loading). The problem with both these specifications is that a static loading requirement has been used to design against falling debris, when in fact,the debris exerts a dynamic load. The other method is the debris net which was previously mentioned. These should be designed and designed and installed in accordance with ANSI10.11 which requires the nets to withstand 17,500 lb-ft of impact energy and for the net plus attachement to withstand 10,000 lb-ft of impact energy. When we consider that a full thickness 2inx10in plank 16 ft long dropped from the eighth floor would equal approximately 8000lb-ft of energy, the requirement does not seem out of line. New York City leads the US in providing this type of protection. All new construction sites require nets to be provided whixh follow the construction activities as they progress up the building. In order to provide continuous protection, two levels of nets are provided and they are leap-frogged up the building. Alternatively, one level is provided and a mechanical hoist system is used to move it up without retracting the nets.

NETS THAT WORK NOTE:
Our system was devised to replace the mechanical system. Our manually moved system requires much less labor. Crane time is not required between floors and there are no hydraulic lines running all over the floor. ( The Professors continue by explaining how fall protection is accomplished in other countries and they offer impact tests to prove nets are stronger than sidewalk bridges.Here is what they conclude.)

CONCLUSION:
1. The rigid sidewalk bridge offers comparatively little protection from falling debris such as a piece of lumber as seen in Fig A. In addition the trajectory of the debris means that without an active form of protection the debris will miss the bridge and inevitably end up on a car or pedestrians. Thus a bridge is of little protection to the public and no protection to the workers on the ground or up on the structure.

2. A dynamic load specification for sidewalk bridges would encourage designers to provide structures that respond better.

3. The approach taken by New York City, as discussed previously using a combination of active and passive protection systems, is the most realistic and practical method to use with the current trends in building in the US. High handrails and mesh screens provide active protection on all floors except those on the upper levels where nets are used as passive protection.

Reprinted by Permission of Dr.Ralph Bennett III, PE,ASCE Please contact us for full text and test results- NETS THAT WORK

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U.S. Patent No. 4838382
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