|
by Mark B. Geiger, M.S.E., CIH, CSP, Arlington, Virginia
|
|
The hierarchy of controls described in Military Standard 882 and accepted safety practice stipulates that, if feasible, the hazard will be eliminated by avoiding the need for entry; or controls such as fixed barriers (e.g., railings) will be used. If other preferred alternatives are not feasible, personal fall-arrest systems are required.
References on design for safety and fall protection [Refs. 3, 12, 14] address implementation of protective measures employing the hierarchy of controls consistent with Military Standard 882. The Department of the Navy Fall Protection Guide for Ashore Activities (developed by the Naval Facilities Engineering Command) [Ref. 3] provides a detailed matrix for evaluation of potential fall hazards and application of control measures.
Guidelines for fall protection have been most comprehensively addressed in facilities design, construction and maintenance. Approaches described in the Department of the Navy Guidance [Ref. 3] are summarized below. Evaluation and engineering control during the planning phase are strongly emphasized. Risk assessment should include review of prior injuries in related facilities or operations and evaluation of the current designs.
Approaches to Evaluation and Control
The hierarchy of control measures and some common measures include:
- Elimination: Designs that avoid the need for work at heights. These include design of equipment that requires periodic servicing such as aerials and street lamps to rotate at the base for access when maintenance is required. Remote sensors may be used to eliminate or reduce the need for access to hazardous locations.
- Substitution: Substituting or replacing the hazard with a less hazardous operation or process. For example, structures may be prefabricated on the ground rather than assembled at heights.
- Isolation: This involves isolating or separating the hazard from employees or others by measures such as providing a fixed barrier at the edge of a high surface from the work area. Design for access with fixed barriers may include railings, use of mobile platforms or other measures that limit the risk of hazardous access. An example includes window-washing platforms that move around the building and roof penthouses with entry at the inward (rather than overhanging) side [Ref. 12].
- Engineering controls: Engineering controls are required when the hazard can't be eliminated, or the need for access to elevated locations avoided by other means. Different equipment, such as mobile lifts, or alternative techniques may provide engineering controls. Application of longer-lasting paint systems inside shipboard tanks may be considered an engineering control because it reduces the frequency of required access.
- Administrative controls: This includes identifying and enforcing alternative work practices that reduce the risk of fall injuries by erection of warning signs or restricting access to certain locations.
- Personal protective equipment: Personal protective equipment, such as personal fall-arrest systems, should be considered when other measures are impractical or not fully effective.
These control measures are not likely to be mutually exclusive. An integrated system of process and risk management employing more than one measure is apt to be required.
Engineering Considerations in Design and Application of Personal Fall-Arrest Systems
Workers cannot safely use personal protective equipment for fall arrest in the absence of general managerial and technical support systems. Personal fall-arrest systems are an integrated system that includes the physical components of a full-body harness, anchorage and lanyard, and the managerial and training programs that must be designed, deployed and managed as an integrated unit.
Design (and related documentation) should support application of personal fall-arrest systems through measures such as pre-identified accessible anchorages and accessible footing. NAVFAC identifies location of suitable anchor points as the most critical control measure that designers should include to support deployment of fall protection throughout facility life cycle [Ref. 3]. Engineering expertise is essential to provide anchor points that can provide the 5,000-pound capacity required by ANSI Z359.1 [Ref. 15] and OSHA Standards (29CFR 1926.502 (d) (15)) and 29 CFR 1910.66, Appendix C [Ref. 16, 17].
Anchorage locations should be as high as feasible to minimize the free-fall distance — which cannot exceed six feet — and prevent contact with the surface below. Total deployment distance is in the range of 18 feet. The combination of lanyard length (six feet), deceleration distance (3.5 feet), worker height (six feet) and desired clearance (three feet), creates a need to secure the anchorage point approximately 18 feet above the ground. Fastening lanyards to guard rails or the floor of a walking surface is not safe because of the increased free-fall distances and probable strength limitations of the anchoring points.
Anchor point and access location must also avoid the potential for "swing falls," a pendulum-like motion that can occur if a worker impacts a horizontal surface while falling or after deployment of his fall-arrest system. Tie-off points should be located so as to minimize this potential, and to allow for a maximum swing away from the tie-off point of 30 degrees [Ref. 3].
Horizontal lifelines require engineering design because the trigonometry of their deployment can create great stresses on loading that occurs on deployment.14
Improper tie off of a rope lanyard or lifeline around an H or I beam can reduce the strength significantly.15
A fall-protection program must also include provision for rescue and retrieval of personnel after a fall [Refs. 3, 15, 18]. Within confined spaces, a co-worker should be able to retrieve the victim using a hoist or other mechanism, while located outside the confined space. Maritime confined space applications pose particular challenges, and it is estimated that remote retrieval is not feasible in many current circumstances.
Designs to accommodate scaffolding and/or fall netting are very important in the construction process. Early and appropriate selection is critical. Reference 2 documents a case where nets costing £4,000 could have replaced scaffolding that cost £12,000 and added four weeks to a building program16.
14 A horizontal lifeline is a fall-arrest system that uses a line spanning between two end anchorages. The assembly includes necessary connectors, in-line energy absorbers and may include intermediate anchorages. Depending on the angle of sag, horizontal lifelines may be subject to an impact force that is greatly magnified above that of the attached lanyard. The OSHA requirement (see 29 CFR 1910.66, Appendix C ) for compliance with fall protection standards and DON 2003 indicate that force amplification for five degrees sag is about 6:1.
15 See OSHA non-mandatory guidelines, paragraph (i) and DON 2003.
16 Information on a designer initiative can be found at http://www.hse.gov.uk/construction.
« previous page | next page »
|
