A Passive Fall Protection System: Safety Nets
The second part of a miniseries on fall protection equipment and techniques
Ed's Note: This article first appeared on cpwrconstructionsolutions.org, a website under the umbrella of the National Institute of Occupational Safety and Health.
Working near an unprotected or leading edge can expose workers to potential fall hazards when there is no fall protection method in place. Falls from elevated heights typically result in severe injuries or death. The risk of injury from falling to a lower level is reduced by using personnel nets which are designed to break a worker's fall by catching them in a net.
Safety nets are a passive type of fall protection designed to catch a worker after they have fallen to help prevent contact with the surface below and to prevent injury. Safety nets are erected around an elevated work area in such a way that if a worker falls from that work area, they will be caught in the net.
Workers often sustain injury since they can legally fall up to 30 feet before hitting the net. Safety nets should only be used when the use of fall prevention such as guardrails and hole covers—which will not allow a worker to fall in the first place—have been deemed infeasible.
There are two major types of safety nets: personnel nets and debris nets
Personnel nets are designed to catch a falling worker to prevent injury to that worker. A personnel net is an example of passive fall protection, meaning they provide protection to workers without any active or conscious effort on their part. In contrast, active fall protection systems, such as personal fall arrest systems, require constant awareness and active participation of the worker to make sure the fall system will provide sufficient protection.
Debris nets are designed to catch construction materials (scraps, nails, tools and falling bricks) to prevent them from potentially injuring workers or pedestrians below. In cases where personnel nets are used, they shall be lined with debris netting of sufficient strength and size to contain tools and materials capable of causing injury.
Safety nets are typically used during steel erection, bridgework, demolition, and maintenance work. Safety nets are an acceptable means of fall protection for holes, open-sided floors, catch platforms and steel/concrete erection. They are often used where large open areas or long leading edges expose workers to high fall hazards. Nets can be used as fall protection on the exterior and interior of buildings under construction.
General requirements for safety nets
- Nets must be installed as close as possible under the walking/working surface, but in no case will an employee be exposed to a fall greater than 30 feet into a net.
- They must be installed in a manner that prevents a falling individual from striking any object below the net.
- Safety nets must be inspected at least once a week for wear, damage, and deterioration.
- Nets must be inspected after any occurrence which could affect its integrity, such as a steel member falling into the net.
- Defective safety nets will not be used.
- Any materials, scrap, tools or equipment that falls into the net must be removed as soon as possible but no later than the end of the work shift.
- The installation of safety nets must be done by individuals protected from the fall hazards they are exposed to during the installation.
- Each net must have a border rope for webbing with a minimum breaking strength of 5,000 pounds.
- The maximum size of each safety net mesh opening shall not exceed 36 square inches nor be longer than 6 inches on any side, and the opening, measured center-to-center of mesh ropes or webbing, shall not be longer than 6 inches.
- All mesh crossings shall be secured to prevent enlargement of the mesh opening.
Nets shall be installed in accordance with the net manufacturer's specifications and instruction. Nets shall be installed as close under the working level as practical, but not lower than 30 feet. They shall be hung with sufficient clearance to prevent contact with the surface of structures below when the user's impact load testing is applied.
There shall be no intervening members between the working surface and the net that could be impacted during a fall.
Safety net extension ratio
Safety nets should extend a minimum of 8 feet out for nets positioned at the same level as the work, and up to 5 feet below the work surface. Use nets with a 10-foot minimum extension width for nets positioned at 5 to 10 feet below the work surface. Use nets with a 13-foot minimum extension width for nets positioned at 10 to 30 feet below the work surface.
Remember, under no circumstances should personnel nets be used 30 feet or more below the work surface.
Safety net inspection
Safety nets must be inspected at least once a week for wear, damage, and other deterioration. Nets should be inspected after any occurrence which could affect the integrity of the safety net system. Defective nets shall not be used and defective components must be removed from service. Materials, scrap pieces, equipment, and tools which have fallen into the safety net must be removed as soon as possible from the net and at least before the next work shift.
Safety nets must be drop-tested at the jobsite after initial installation and before being used as a fall protection system, whenever relocated, after a major repair, and at 6-month intervals if left in one place.
The drop-test consists of a 400-pound bag of sand approximately 30 inches in diameter dropped into the net from the highest walking/working surface at which employees are exposed to fall hazards, but not from less than 42 inches. A tag line of sufficient strength shall be attached to the test weight to prevent it from falling to the surface below should it penetrate the net.
When the employer can demonstrate that it is unreasonable to perform the drop-test, the employer shall certify that the net and net installation is in compliance with the provisions by preparing a certification record prior to the net being used as a fall protection system. The certification record must include an identification of the net and net installation for which the certification record is being prepared; the date that it was determined that the identified net and net installation were in compliance and the signature of the person making the determination and certification.
The most recent certification record for each net and net installation shall be available at the jobsite for inspection.
Debris nets are designed to catch falling debris, such as tools, foreign objects, falling concrete, and other construction debris, to protect workers and pedestrians below. Safety nets and debris nets are often combined. The smaller mesh nets used to catch small debris are used in conjunction with larger and stronger nets used to catch workers.
Debris nets must be secured on top of the personnel net and must not compromise the design, construction, or performance of the personnel nets. In these cases, the nets must be cleared of debris on a regular basis to ensure a falling worker's protection.
The strength and size of the mesh must be sufficient to sustain the impact, catch the size, and sustain the weight of the objects that are likely to fall. Typical net sizes (both personnel and safety) range from 1/4 inch to 3/4 inch mesh.
Netting for use with guardrail systems
When equipment or materials are piled higher than the top edge of a standard toe-board on a guardrail, debris nets must be installed from the top rail to deck level to provide overhead protection for employees working below.
When properly installed from a top rail and secured directly to deck level, some nets satisfy OSHA requirements for mid-rail and toe-board protection, as well as overhead protection.
Personnel and debris net requirements
The American National Standards Institute (ANSI) has published consensus standards related to safety requirements for the selection, installation, and use of personnel and debris nets during construction, repair, and demolition operations. This document is titled ANSI A10.11 Safety Requirements for Personnel and Debris Nets and was revised in 2010.
ANSI voluntary consensus standards are an excellent source of reference material and are widely recognized in the industry.
Productivity may go up
An increase in production may occur when workers, particularly those working at height, feel safe in the knowledge that they are protected from injury or death that may occur from falling from the work area.
By using fall protection methods such as safety nets, production may increase because workers have a peace of mind knowing that the safety net is there to catch them and spare them injury in the case of a fall.
Installing and removing nets
The installation of nets requires careful planning. Workers who are involved in installing and removing safety or debris nets must be protected from fall hazards by aerial lifts, personal fall arrest equipment, or a personal restraint system. Nets and/or horizontal lifelines can provide many solutions to fall hazards if they are planned, installed, and used.
Sources of supply:
Washington University: Equipment for residential construction classified by the type of equipment and the phase of construction: http://www.ot.wustl.edu/fptech/homepage.htm
Guardian Fall Protection: http://www.guardianfall.com | 1-800-466-6385
—This article was written by Mark Fullen and Kristen Savage of West Virginia University for cpwrconstructionsolutions.org