The initial phase of the investigation was to identify the primary sources of injury. The MSHA Accident, Illness and Injury database was reviewed to obtain accident statistics involving large-format batteries from 2008 to 2012. The analysis emphasized nonfatal, days lost (NFDL) injuries [4].

The cases were selected by filtering the incident records using a keyword search to focus specifically on cases that mentioned the word “battery” in the accident narratives. This approach yielded a total of 324 reports. Of the 324 reports, 128 incidents could be attributed to the maintenance and repair of lead-acid batteries. The remainder of the incident narratives containing the word “battery” described incidents involving battery-powered vehicles or other battery formats (e.g., cap lamp batteries), which were outside the scope of this investigation. The applicable reports were then reviewed and categorized to gain insights into the root causes.

In addition to those cited earlier, other resources used included a review of battery safety prevention program tips found at MSHA’s Accident Prevention Program webpage (http://www.msha.gov/Accident_Prevention/minetype/ugcoal.htm) [5] and manufacturers’ installation and maintenance manuals [6]. This review focused on large-format lead-acid batteries typically used in underground mining equipment.

Site visits and informal interviews were conducted within the various battery industry sectors, including manufacturing, protection, and refurbishment companies, as well as the end users at mining operations. Each stage of the large-format battery design and manufacturing process was observed while exploring potential safety issues. Three battery manufacturing/refurbishing companies, two original equipment manufacturers (OEMs), three mine sites, and the international mine expo were visited; and discussions were held with engineers and end users at various locations. The visits were also supplemented by phone and e-mail discussions to gather information about large-format battery safety when site visits could not be scheduled.

The size and weight of lids may contribute to back and shoulder injuries. Several lid configurations were observed in the field and varied from long rectangular lids to smaller square lids, depending on the manufacturer and equipment type. The two configurations are depicted in Figs. 3 and 4.

Weight distribution and handle placement pose challenges to users in terms of body positioning when raising the lids. The challenge is worsened in low coal seams where the limited vertical space creates more difficulty. The smaller size of the square lids can relieve the strain caused by the frequent need to open and close the lids for maintenance and repair work. The ease of opening the lids also affects the performance of maintenance and repair tasks, because a repairman is more likely to put off preventive maintenance if lids are difficult to open.

Some of the overexertion and strain injuries associated with lids can also be attributed to the types of materials being used in their construction. MSHA prescribes criteria for designing battery assemblies in CFR Title 30, Part § 7.44. These criteria focus on the tensile strength of the material, the impact resistance of the assembly, and the flame resistance of the components used. To meet these criteria, the lids are commonly made of hot rolled steel. The hardened steel protects the batteries from being pierced or crushed in the event of a roof fall. However, the metallic lids can also introduce hazards such as the potential to provide a conductive path for short circuits across battery terminals in the event of a damaged battery assembly. Although measures are taken to minimize that risk, such as the use of polyvinyl chloride insulation, the use of steel increases the weight of the lids and may impact musculoskeletal injuries.

Accordingly, manufacturers are also proactively considering the application of composite materials to construct new battery assembly lids and covers to reduce weight while maintaining the required strength and fire resistance. By designing battery assembly lids with a lighter nonmetallic material, manufacturers may contribute to reducing the number of musculoskeletal injuries suffered from handling the heavier rolled steel assemblies.

MSHA does provide requirements for battery assemblies constructed of alternative materials. The regulations and requirements, which are outlined by CFR Title 30, Part §7.44(a)(2), state that any battery assembly not made of hot rolled metal must possess “tensile strength and impact resistance of battery boxes for the same weight class.” In addition to the tensile strength, the new material must also pass flammability and acid resistance testing outlined by CFR Title 30, Part §7.44(a)(4). Examples of alternative materials include hardened phenolic composites or injection-molded composites. While the use of alternative materials has been explored in countries such as South Africa, this area requires more research and must follow the proper approvals process before it can be implemented across the mining industry. A major benefit for doing so is the potential impact of reducing musculoskeletal injuries and promoting proper battery charging practices such as charging with all lids raised due to the reduced weight of the lids.

An alternative solution to the weight issue presented by the heavy steel lids is the implementation of lift assists. Some manufacturers offer pneumatic lift assists to help address this risk (see Fig. 5). A lift assist helps raise the lids safely by reducing the musculoskeletal strain to which a mine worker is subjected. Thus, injuries attributed to the frequent raising and lowering of the battery lids for charging, maintenance, and repairs may be significantly reduced. These lift assists are relatively inexpensive and easy to replace if damaged. Furthermore, the costs of these assists may be offset by reducing the costs associated with lost-time injuries.

Another factor that contributes to the effort required to open lids is rusted hardware, which results in increased hinge friction. Lid hinges rust quickly in a wet mine environment. Some manufacturers offer stainless steel hinges to reduce the rusting problem.

Manufacturers also recommend the use of hinge covers. These covers serve a dual purpose as they effectively keep rock dust and dirt from the hinges while reducing the accumulation of debris inside the battery assembly (see Fig. 6). Debris accumulation can create a potential for a short circuit across battery terminals that may result in a battery fire or explosion. Note in Fig. 6 the amount of debris built up on the battery assembly surface that was effectively kept away from the battery’s surface area and terminals by the use of hinge covers.

The charging cables and type of cable connectors play a major role in a battery’s arcing potential. There were a number of cases, discussed during the interviews, which involved arcing when disconnecting cables. The discussions revolved around the susceptibility of dated two-pole connectors and cables to arcing. While the two-pole connector cables are no longer allowed in some states, there are still many small operations that use these connections because of legacy equipment and cost.

A five-pole look-ahead charging cable connector is a major improvement to the two-pole connector. This configuration, which is depicted in Fig. 7, consists of positive and negative pins, a ground pin, and two pins used to “look ahead.” The two look-ahead pins serve the purpose of interlocking with the charging coupler and ensuring that there is a proper connection prior to starting the charging cycle. This feature also eliminates arcing when the charging cables are disconnected from the battery by tripping a circuit breaker before the power contacts are separated.

Accident/illness/injury statistics show a small number of cases involving arcing when cables were pulled from the battery assembly (see Fig. 2). These reported cases, which are included in the arcing/acid burns category, often occurred during the maintenance and the charging of batteries because the batteries were not properly deenergized prior to the cables being disconnected. From an engineering standpoint, the addition of a circuit breaker on a battery assembly, as shown in Fig. 8, reduces that potential by providing a local method for deenergizing a battery.

While some OEMs are making this feature standard on 240-V models, it is not a practice that is being implemented by all mining companies. These interventions come at an added expense, which many operators may be unwilling or unable to incur. At an estimated $10 000 per installation, manufacturers realize that some mine operators will forgo this option unless there is a regulation requiring the use of such a safety feature. They consider this to be particularly true with intermittent-use Fig. 9. Debris and leakage buildup on terminals. vehicles, such as scoop tractors, where the cost associated with adding this feature causes end users not to choose it. However, the use of a battery circuit breaker can prevent arc flash burns sustained by workers while pulling cables from connectors prior to proper deenergization.

Although the lids and covers of battery assemblies are made with hardened steel and are often insulated on the inside surface, intercell connector caps also provide another layer of protection. These intercell connector caps enclose the terminals and provide a thin layer of plastic to prevent arcing across the terminals. Noteworthy is the apparent absence of an intercell connector cap in Fig. 1. The intercell connector caps also serve the purpose of preventing arcing and shorting across terminals when tools are dropped or left in the battery assemblies. Although these intercell connector caps provide protection against short circuits between terminals, battery refurbishing companies revealed that these caps can have a negative impact by hiding electrolyte leakage and the buildup of debris at the battery terminals, as shown in Fig. 9, which can go unnoticed for an extended period. This can result in fires and even explosions caused by short circuits.

Hydrogen is produced from the electrochemical process that occurs when lead-acid batteries are charged. Hydrogen has an explosive range of approximately 4%–74% in air and can initiate an explosion even when the oxygen content of the air is as low as 5% [3]. Monitoring hydrogen levels to prevent the accumulation of dangerous concentrations could eliminate the potential for an explosion. Personnel at one of the mines visited are currently exploring the use of infrared gas monitors to detect the accumulation of hydrogen in battery charging stations. This feature can alert mine workers of impending dangerous concentrations of hydrogen so that appropriate measures can be taken to neutralize the threat through ventilation controls.

This research effort focused on large-format lead-acid batteries due to their dominant use throughout the mining industry for power haulage, utility, and personnel-carrier vehicles. However, other chemistries are being explored to improve safety and efficiency related to battery lifecycle and energy produced. These battery types are relatively new and, by most accounts, are considered cost prohibitive. For example, lithium ion batteries are one of these newer chemistries being considered as a replacement for the lead-acid batteries; however, the cost associated with implementing lithium ion technology on such a large scale and concerns regarding the safety issues associated with incorporating them in such a large volume have discouraged their use. A majority of the manufacturers interviewed indicated that lithium ion batteries are cost prohibitive and that their use would not be feasible until the technology is further developed and is more affordable.

Another chemistry considered is sodium metal halides. The use of metal halide chemistries is currently being pursued by the mining division of one OEM. While there is much to learn about this battery chemistry and its operating parameters, its major appeal is that it would eliminate the frequent maintenance requirements that are associated with a lead-acid battery. Battery manufacturers developing this chemistry for use in mining applications stated that this chemistry provides higher energy density, weighs half the amount of typical lead-acid batteries, has a higher tolerance to extreme operating conditions, contains no harmful chemicals, and is virtually maintenance free. These features certainly have the potential for reducing injuries associated with battery maintenance.

Training is often provided by the battery manufacturers and the OEMs in the form of printed literature, videos, and on-site hands-on training. These training methods focus on the basic concepts of how a battery works, proper charging, and maintenance practices for cleaning and changing cells. These sources continue to play a significant role in mine worker safety. More recently, some mines have employed and trained mine workers to become dedicated battery technicians. The battery technicians are responsible for maintaining and transporting the batteries to their host vehicles in addition to record keeping for charging and cleaning cycles, visually inspecting batteries for damage, and determining repair schedules as needed. Assigning only qualified technicians to perform the day-to-day maintenance could help reduce accidents attributed to personnel not following proper handling recommendations established by battery manufacturers and performing inadequate repair techniques on batteries.

Another important safety consideration relates to wearing the proper PPE during battery maintenance and repair tasks. Performing a job hazard analysis for each maintenance and repair task could help determine the proper levels of PPE that should be worn. Chemical-resistant gloves, aprons, and face shields may help prevent battery acid injuries highlighted by the accident/illness/injury database analysis.