Edited by Rowena Davis

Part 2:

Five Prominent Hazards

The hazards commonly encountered by both cranes and aerial lift operators and users are deadly, yet preventable by design while priced cost-effectively. Five prominent hazards are common to both cranes and aerial lifts:

• Powerline contact
• Overload
• Error provocative operator controls
• Blind zones
• Inadequate access

Illustration 15, a chart, which illustrates the hazard, failure mode, consequence and the appropriate engineering control for these five common hazards, presents a basis for examination in greater detail.

Illustration 15 Hazard Chart

* One hand and two feet or two hands and one foot contacting at all times

Common and individual hazards applicable to cranes and aerial lifts will be referenced in Appendix A: Litigated Cases, with an example of a typical failure mode that has been subject to litigation. Hazards are separated in numerical sections.

Section 1: Powerline Contact

Unintentional contact with powerlines by cranes and aerial lifts continues to be a principal source of catastrophic events, including serious and painful injuries or gruesome death. The major powerline contact hazard is armed by the use of metal booms of cranes and aerial lifts that can be raised into powerlines. The height of the booms creates the hazard of boom contact as well as the hazard of hoist line contact with a powerline.

The Occupational Safety and Health Act (OSHA) requires a minimum 10- foot (10’) clearance from powerlines. Unfortunately, this requirement has proven to be unreliable, as it is constantly, unintentionally violated by human error and visual misperception. Mistakes made by this inaccurate worker practice cannot be stopped or corrected due to the fact that thin air provides no barrier at the minimum distance from a powerline. Compliance with this requirement relies solely upon the accuracy of human perception, which is not possible to achieve, rendering enforcement of the 10-foot OSHA regulation impossible. Reliance upon human performance of visually maintaining a thin air clearance of crane boom, hoist line, other parts of a crane, and aerial lifts from powerlines has been an exercise in futility. (See Appendix A Section 1(a): Crane powerline contacts and Section 1(b): Aerial lift powerline contacts for a list of cases.)

Review of 1,500^? occurrences from the period of 1950 to 2006 indicates that thin air clearance standards to avoid powerlines needs to be rewritten to include the use of safety appliances. The Hazard Information Foundation, Inc. (HIFI) authored a research report on history and prevention of powerline contacts ^? that explains in detail the causes of this serious hazard syndrome. Examination of the 1,500 crane powerline-contact litigation records reveals a key factor: The contact in the overwhelming majority of cases was made mid-span on the powerline between the supporting powerpoles or towers. My personal visits and reviews of many accident sites to determine the cause found that the injured workers were the victims of unforgiving circumstances that include a lack of visual cues to alert them to the presence of a powerline.

^? Research report: “Safety Interventions to Control Hazards Related to Powerline Contact by Mobile Cranes and Other Boomed Equipment” distributed in 2004 by the Hazard Information Foundation, Inc (HIFI), Funded by the Center to Protect Workers’ Rights (CPWR).

Circumstances of contact occurrences consistently included an absence of warning to the presence of an overhead powerline, no mechanical aid restricting the operating scope of the boom to within a safe envelope, and no guarding with insulation. The use of redundant safeguards would significantly overcome the unreliable human performance to prevent equipment powerline contact. The steps needed to control this devastating hazard can be achieved with a change from the 10-foot thin air clearance mandated by current government regulation to management incentives to implement the following measures:

1. Require construction plans and specifications to remove, relocate, bury, or de-energize powerlines before the crane or aerial lift appears at the work site.
2. Establish a worksite procedure to always barricade, flag, or mark the Danger Zone on the ground, where it is easily seen and shall not be violated (see Illustration 16). OSHA should include a requirement for a standard written procedure to first map the 10-foot powerline danger zone on the ground as shown in Illustration 16. This practice will provide guidance on how to stay out of the danger zone created by powerlines to both the crane operator and the rigging crew.
   
   Illustration 16: Danger Zone
   
   Map and Barricade the 30 ft. wide Danger Zone
   (15 feet on each side of the powerline poles)
   
   
3. Develop a process to install accessories such as the proximity alarm, which warns of the presence of powerlines, on all cranes. Recently developed wireless proximity alarms can be planted in various locations on boomed equipment, and provide more effective protection than a single antenna³. Other safeguards include an insulated link (to prevent the flow of electric current) and a range-limiting device (to keep boom movement within a defined parameter). Elimination of powerline contact hazards requires utilization of redundant engineering controls (multiple safety appliances). Redundant safety features that will provide effective controls are the only way to ensure for reasonable back-up safeguards in the variety of work-site situations faced by construction workers. The proximity alarm identifies the presence of powerlines; the range limiting device restricts boom movement to a safe, predetermined envelope zone. The insulated link provides a ground fault protection to the workers guarding the load. The concept of redundancy starts with the use of a proximity alarm to alert the crane operator and crew that they are working close to a powerline.
   
   ³ Irvin Nickerson of Las Vegas, Nev., has developed and patented a wireless proximity alarm sensor that can be placed on various locations on the crane boom. This new method is even more effective than the conventional wire antenna.
4. OSHA requirements should provide workers and employers with options to control the hazards via the tools of safety appliances, and encourage the creation of standard procedures that are reasonable safe-work methods by worksite personnel. Safety should become a process where management provides the tools and employees follow safe work processes specific to their circumstances.
5. Cranes fitted with aerial baskets attached to a conductive metal boom or such booms on aerial lifts shall not be used near powerlines. For activities conducted near a powerline, a non-conductive basket with a nonconductive insulating cage fitted to the basket should be designed to provide an effective guard against unintentional contact with an energized powerline by the person in the basket. This cage will provide a reasonable degree of protection to those who service cable TV and telephone systems⁴, engage in tree trimming near energized powerlines, install traffic signals, or similar tasks. However, this equipment will not serve as a safety feature to allow untrained personnel to work within the OSHA requirement that delineates a ten-foot clearance from powerlines. See Illustration 17.
   
   ⁴ According to the National Electric Safety Code ANSI C2, Table 231-1 allows clearance below an energized bare conductor as little as 24 inches.
   
   Illustration 17: Boom Cage
   
   Conceptual design of a non-conductive framework boom (above): The non-conductive basket prevents the occupant in the basket from inadvertent contact with bare live powerlines. This device provides a backup for workmen using a non-insulated aerial lift.
   
6. Alternate or remote controls for cranes and emergency controls for aerial lifts shall incorporate design features that prevent a ground fault through a user who is standing on the ground.
7. Operating personnel shall be trained in the above six requirements and procedures necessary to prevent crane or aerial lift powerline contacts. A certificate of this training shall be included as a condition of operation and/or use of a crane or aerial lift. A record of the contents of this training shall be maintained to ensure that the safeguards listed above are provided and these safety procedures are being followed.

Each type of aerial lift has unique hazards of its own. A brief history of these devices provides an insight as to why they were designed with inherent hazards. Aerial lifts were first developed to service the warheads of early air missiles. These lifts needed to have a non-conductive boom to prevent the flow of static electricity. These first lifts were of a simple design that consisted of a tubular fiber glass boom with a plastic basket. The controls were in the plastic basket so the operator who was in the basket could control the boom of the lift. The boom was mounted on a small turntable on a pedestal placed upon a lightweight truck bed. This concept was quickly adopted by the electric utilities for powerline installation and live line hot work. Early models included a two-section articulate boom with an uninsulated lower section. Also, some had uninsulated, short metal jib booms used to lift transformers, and others had metal joy stick controls that created a fault circuit for the operator if a phase-to-phase powerline contact occurred when the jib stuck a phase conductor. Since that time, insulation on both lower and upper sections of the boom, as well as other design features of lifts used in the electric utility industry, has been greatly improved to provide protection to utility linemen. (This type of work also requires a number of additional safety appliances and personal protective devices, including insulated line covers, rubber gloves, rubber sleeves, and non-conductive hard hats.)

Aerial lifts used for tree trimming, installation of traffic signals, replacement of highway lights, telephone and cable TV installation, and other tasks that bring workers in close proximity to powerlines are susceptible to this hazard. The American National Standards Institute (ANSI) National Electric Safety Code (NESC) (C2) Table 325-5 allows for a clearance of only 40 inches below uninsulated powerlines of voltages up to 8.7 kilovolts. Uninsulated aerial lifts are banned from use next to powerlines. For a number of reasons this prohibition is often violated. Qualified electric utility linemen who work close to powerlines are often victims of unintentional phase-to-phase powerline contact, despite their use of insulated baskets. Use of non-conductive cages discussed and illustrated (see Illustration 17) in this document is a necessary prevention method of powerline contact injury.

Aerial lifts and the hazard of powerline contact have two areas of concern. First: Aerial lifts used by the electric utility industry have their own set of rules when working within the 10-foot danger zone next to powerlines. Their aerial lifts must comply with ANSI.SIA A92.2 (Vehicle-Mounted elevating and rotating aerial devices 2001 and OSHA requirements 1910.137 and 1926.950-960 subpart V: Power Transmission and Distribution). Second, uninsulated aerial lifts used for other tasks are often situated immediately adjacent to powerlines (see OSHA 1926.550(a)(15)(i/iii) Clearance from powerlines). Decreased clearance should not occur unless an insulated lift is used by a journey lineman in compliance with ANSI A92.2. The majority of injuries from powerline contacts occur when the aerial lift does not have an insulated boom and basket, or the work site did not have the benefit of pre-job planning to de-energize or remove powerlines.

Section 2: Overload

Overloads resulting in upset, and in some instances include structural failure, are a hazard common to both cranes and aerial lifts. Nearly all of these failures can be prevented with a Load Moment Indicator (LMI), a device that provides warning of overload to the operator. LMIs also intercede to prevent further movement of the boom, preventing the lift of loads that exceed the rated capacity of the crane or aerial lift. All cranes and aerial lifts without this appliance are inherently dangerous. (See Appendix A Section 2(a): Crane Upset for a listing of prominent crane overload litigation, and Section 2(b): Aerial Lift Upset litigation.)

Hydraulic telescoping or articulate boom cranes are most often confronted with the hazard of upset or boom collapse from overloading. Cranes can be vulnerable to upset with either extended or retracted outriggers. A reduction in these occurrences has been achieved with the use of Load Moment Indicators (LMIs). The newest types of LMIs for hydraulic telescoping boom cranes have software programs that provide a rated capacity for all boom positions with both outriggers extended and in place or retracted.

From review of over 1,000 crane upsets occurring over a thirty-year period, it can be projected that an upset occurs once in about every 10,000 hours of crane use. Nearly 75% of these upsets were the result of error-provocative circumstances that caused the operator to inadvertently exceed the crane’s lifting capacity. The good news is that in the decade of 1993-2003, the occurrence of crane upset from overloading in the categories of outrigger retracted and extended started to decline. This trend can be attributed to the industry acceptance and use of load moment indicators (LMIs). New technology of wireless LMIs make it easier for them to be installed on both telescoping and latticework boom cranes. Wireless systems are exceedingly helpful in providing utility for converted tower cranes. However, when averages of failures are examined, they remain constant. Even with fewer upsets occurring, the failure modes remain the same, as the older cranes are not equipped with LMIs. The following breakdowns were made:

15% were in the travel mode 39% were making swings with outriggers retracted 15% were making a pick with outriggers retracted 14% were making a pick or swing with outriggers extended 6% were making a pick or swing, use of outriggers unknown 7% were due to outrigger failure 4% were from other activity 3% resulted in fatalities 8% resulted in lost-time injuries 20% resulted in significant damage to property other than the crane

Licensing programs of crane operators should include certification of the use of LMI systems to help alleviate incidents caused by incorrect use. When aircraft pilots became licensed in the use of electronic navigation systems, this knowledge reduced the occurrence of craft becoming lost in fog or darkness. Crane operators licensed in the use of the LMI will reduce the occurrence of upset. In many instances of upset of a crane equipped with an LMI, the crane operator did not utilize the LMI by turning it off, or was unfamiliar with its proper use. It is crucial that the operator is familiar with the basics of LMI use, because the LMI needs the correct measurements as input in order to calculate safe angles and degrees of lifting capacity. Many cranes upset because operators enter incorrect information. Construction managers should have at least rudimentary knowledge of LMIs in order to be able to double-check a crane operator’s measurements. If no one on the site has adequate knowledge in LMI requirements, the blind lead the blind, and a safe lift is not guaranteed. A licensing program of crane operators that includes certification as competent in the use of the LMI provides a higher degree of authority to accept a safe lift and reject an unsafe lift. All crane operators should be certified by the manufacturer of the LMI of which the crane is equipped. Such credentials warrant a higher pay scale. This compensation is a bargain when compared to the high cost of crane upset by an unqualified operator or incompetent supervision which overrules a certified operator.

There have been documented cases of outrigger failures from structural defects. The hazard of inadequate soil support remains a continuing peril. Soil conditions range from wet sand that can support only 2,000 lbs/square foot to dry clay that can support 4,000 lbs/square foot to well-cemented hard pan that can support as much as 10,000 lbs/square foot⁵. Outriggers sinking into the soil even as little as half an inch can reduce the lifting capacity of a long boom. For this reason the crane needs to be set on mats or outrigger pads whenever soil conditions are questionable. The footings for a tower crane always need to be calculated by a licensed engineer proficient in soil mechanics who will stamp and seal the design to ensure that the footing is strong enough and absolutely level.

⁵Pg. 38, Crane Hazards and their Prevention, MacCollum.

Proactive construction contract specifications should include a clause stating that tower cranes should be inspected by a third-party certifier before and after set-ups every time they have been used. The erection of both mobile and fixed-base tower cranes need to be supervised by a person qualified by the crane manufacturer. In addition, all cranes should be inspected annually by a nationally recognized crane inspection service.

Only freely suspended loads should be lifted. Freeing a form panel stuck to freshly cured concrete, raising piling with a vibratory pile driver, or lifting a floating log of unknown weight all involve loads that are not freely suspended. Sometimes an operator needs to be able to let the load free fall to overcome an unintended overload from loss of stability (such as overload). Additional hazards can result from the use of logging tongs to guide a heavy floating object. In one situation, management provided the crane operator with logging tongs attached to the hoist line to guide a heavy floating log over the spillway of a dam. When the log was caught by the current and could not be released from the tongs, it pulled the crane into the water and the operator drowned.

Flatbed trucks that have hydraulic cranes mounted on them have a very high center of gravity and are known to upset while being driven (roaded) or being parked by the edge of a road where the road shoulder slopes away. It appears that the electronic stability controls that have been so successful in preventing upset on SUVs would prove to be an effective safety feature on these flatbed mounted cranes.

Aerial Lift Upset

Both truck-mounted and self-propelled aerial lifts have a high center of gravity and upset in the travel mode. This instability can be attributed to an absence of an electrical stability system. Those with outriggers need functioning interlocks to limit boom movement to times when outriggers are extended and in place. Aerial lifts with counterweights must effectively intercede to limit boom movement to within the scope of design for the maximum foreseeable weight of the operator and foreseeable specified weight of tools or materials.

Self-propelled aerial lifts are very prone to upset on sloping and potholed surfaces. Self-propelled scissor lifts can easily overturn if one wheel slips into a hole. Some models have a much lower clearance from the floor, which prevents the scissor lift from falling over.

According to Maura Poternoster, risk manager for Insurance Services for American Rental Association⁶, many aerial lift injuries stem from a failure to inspect and maintain the equipment before it is rented to users. Some 40% of claims involve tipover caused by a failure to inspect. Annual third-party inspections of aerial lifts would reduce failures that may lead to upset.

⁶ From article in :Lift and Access, April 2007

Section 3: Error Provocative Controls

A third common hazard arises from error-provocative operator controls. Faulty or unguarded controls can cause unintended activation of the boom or cause freefall of the load. (See Appendix A Section 3(a), which lists error-provocative control litigation for cranes, Section 3(b) for aerial lifts.)

Crane controls that allow indirect dropping of the load are a frequent defect on older friction-powering latticework booms in cranes without powerlowering.

Aerial lifts have guardrails around the parameter of the panel, but the panel remains open for easy operator contact^?. Inadequately guarded controls on aerial lifts that are accessible to the body of the operator are dangerous. Guarding controls prevents unintentional body contact and unintentional activation. The panel should have a top guard bar, as is illustrated by the series of illustrations below.

^? This subject is further addresses in the Research report: “Safety Interventions to Control Hazards Related to Powerline Contact by Mobile Cranes and Other Boomed Equipment” distributed in 2004 by the Hazard Information Foundation, Inc (HIFI), Funded by the Center to Protect Workers’ Rights (CPWR).

Illustration 18: Unguarded aerial lift controls

Illustration 19: Guarded aerial lift controls

Illustration 20: Guarded aerial lift controls

A number of ANSI standards have required that the control panel “be protected against inadvertent operation” for years. The requirements are listed as follows:

• ANSI 92.2 Vehicle Mounted Elevating and Rotating Aerial Devices 1990, 4.3.1: “Aerial devices primarily designed as personnel carriers shall have both upper and lower control devices. Controls shall be plainly identified as to their function and protected from damage and inadvertent activation (emphasis added). The boom positioning controls shall return to their neutral position when released by the operator.”
• ANSI A92.5 Boom Supported Elevating Work Platforms, 1992 4.10: Controls 410.1- Upper controls (e): “Be protected against inadvertent operation.”
• ANSI A 92.6 Self Propelled Elevating Work Platforms 1990, 4, 6 Controls (5): “Be protected against inadvertent operation.”
• State of California Code of Regulations 3462, Elevating Work Platforms Equipment (d): “Any powered elevating work platform shall have both upper control devices. Controls shall be plainly marked as to their function and guarded to prevent accidental operation (emphasis added). The upper control device shall be in or beside the platform, within easy reach of the operator. The lower control device shall have the capability to lower the platform where the operator’s safety is in jeopardy.”

The National Safety Council’s Study of Aerial Basket Accidents Volume II 1967-71 has 20 examples of injuries from the hazard of inadvertent control activation. This hazard can arise when the operator’s body (chest or waist) can intrude into the control area. Body sizes are well defined in the Society of Automotive Engineers (SAE) J833 Human Dimensions handbook. Also, Woodsen has some data in the Human Factors Design Handbook (McGraw-Hill 1981). These same dimensions were listed in the Human Engineering Guide to Equipment Design by the American Institute for Research in Washington, D.C.

Exposed (unguarded) toggle switches have an unsafe design that is currently popular in many aerial lift control systems.

Illustration 21

Unguarded Toggle Switch

Illustration 22

Guarded Toggle Switch

Every control panel should be examined for the hazard of unguarded toggle switches. The conventional toggle switch can be made safer, as done by most Asian and European automakers, by relocating the toggle switch to a vertical position so that downward movement lowers the car window and only upward movement can cause the car window to raise and close. (Exposed rocker switches in American cars have resulted in a number of child deaths.) The U.S. Department of Transportation (DOT) motor vehicle safety is requiring a design change by 2008 for safer window switches. The same change should be provided for toggle switches in aerial lifts to prevent unintended upward activation errors.

Controls that do not return to neutral when released are the source of inadvertent and unintentional operation. This failure mode is most frequently attributed to two causes:

• Controls that fail to automatically return to “neutral” are in danger of unintentionally triggering or continuing movement.
• The return to neutral occurs, but the panel is made from inexpensive and unreliable relays that are vulnerable to sticking, as they weld themselves shut. This malfunction creates a faulty switch response.

Trolley boom cranes have, in the past, had some electrical control system failures of the relay circuit breakers malfunctioning and causing erratic boom operation. Hopefully, most of these cranes are no longer in use, but when one is found to still be in use, the crane control system needs to be checked by a licensed electrical engineer and certified that the relays are of a reliable quality.

Section 4: Blind Zones

Blind zones affect safe operation of both cranes and aerial lifts. On cranes, the crane operator must trust the signal personnel to complete a lift or to move the crane safely. (See Appendix A, Section 4(a), for Blind Zone litigation on cranes.)

Illustrations 23-25 show the areas of vision compromise. Blind zone areas are not uniform, as shown in illustrations. From an outside perspective, it is very difficult to judge the places where the operator’s vision may be compromised. Signal personnel should be familiar with the parameters of blind zones on different types of equipment.

Illustration 23: Manlift from viewpoint of Eye level 10 ft. - 0 in. above ground level

Illustration 24: Hydraulic crane with viewpoint from Eye level 7 ft. - 0 in. above ground level

Illustration 25: Straddle Lift truck from viewpoint of Eye level 14 ft. - 8 in. above ground level

In addition to ground-level blind zones, the operator in the basket is continually vulnerable to objects that may be directly above the operator’s head. The presence of overhead trusses, cable trays, and piping or ductwork may create a dangerous overhead blind zone. The assumption that the operator needs only to “look up” is a myth, as people are single-channeled and tend to look downward. The combination of this behavior and an individual’s attention being taken by performing a task creates a situation where the individual is unaware that they are approaching an overhead hazard, which may be behind them.

The December 4, 2006, cover story of Engineering News Record, “Out of the Blind Zone,” emphasizes the need for safer radio communication with uniform instructions. A retired crane operator states that guiding an invisible load is the most dangerous crane activity. Good communication is crucial to making a safe list when the operator is unable to see every point in the load’s trajectory. Standardized voice signals in short, two word phrases to crane operators would reduce confusion in lift instruction and improve communication between operator and signaler.

Blind zones on aerial lifts are primarily related to circumstances where the operator must look into the sun in some directions of travel. In these circumstances, the operator cannot see powerlines. This hazard leads back to square one: powerline contact, which requires a prohibition of the use of aerial lifts around powerlines except for electric utility operations with insulated systems and other trade requirements. The operator of a self-propelled aerial lift does not generally look overhead. Thus, the space above the crane becomes a blind zone, and the boom can inadvertently be raised into overhead powerlines or, indoors, into a ceiling truss or cable trays. The operator’s cage shown in Illustration 17 provides a way to guard against this hazard.

The most prominent hazard of a straddle crane is a blind zone that allows the wheels to crush workers who are unaware of crane movement. (See Appendix A, Section 4(a) for a list of cases.) When the operator’s station is not on the top of the straddle crane where he or she can see all four wheels, the requirement for safety devices is clear. Safer alternate design requires closed circuit TV monitors, near object detection and travel alarms, and wheel guards/emergency stop systems. Closed-circuit video systems for security cost less than $300 and become a low-cost method of blind-zone elimination.

Section 5: Inadequate Access

The safety of an operator begins with stable access to their post. Different types of cranes present different access hazards. (See Appendix A, Section 5(a) for unsafe access cases.) Hazards unique to crane type are presented as follows:

Latticework boom cranes: These large cranes often have an “A” frame to raise the boom supporting pennants above the level of the cab. This frame must be assembled with workers on top of the crane cab. (See Illustration 2.) Workers need fixed ladders and protective railing to climb onto the crane cab safely.

Tower cranes: Tower cranes several hundred feet high could, in some circumstances, be equipped with a walkway from the building under erection or an elevator within the main shaft to increase the safe access of the tower crane operator. To avoid a long climb for a restroom break, some cranes have attached a portable toilet to the top of the counterweight boom of hammerhead tower cranes.

Aerial lifts: Traditional design of aerial lifts creates the hazard of difficult and awkward access into the operator’s bucket. A gated basket would alleviate the unsafe and awkward access created by the usual practice of climbing over the top of the basket and into the deep well of the basket. The route to the basket should include railings as needed.