Published In February 2001
A worker was injured when he tripped after stepping onto an electrical junction box. This junction box, together with electrical conduits, had been installed on a floor surface adjacent to a newspaper bundle conveyor at the loading ramp of a large daily newspaper publisher. The worker was responding to an emergency after bundles of newspapers coming from the print shop had backed up. The floor-mounted conductors, conduits, and boxes had been provided to energize mechanical equipment for conveying and bundling newspapers that were ready for loading and distribution. A system was to be automated whereby bundles of newspapers would be conveyed from the printing presses down chutes directly to delivery trucks. Before installation of the automated system was completed, this operation required the constant presence of personnel who were working while standing and walking on the floor at and adjacent to the conveyor and bundling machinery. Their job was to carry the bundles of newspapers from the platform to the trucks, pending completion of the automated system. The electrical equipment constituted tripping and stumble hazards to workers during the machinery installation period, as well as to maintenance personnel, who would require access to the area even after automation was completed. Even if a person does not actually fall, obstacles on a walking or working surface offer serious orthopedic injury hazards, due to sudden startle reactions and muscle exertions upon sudden encounters. The general contractor installed temporary wood platforms after the accident in order to provide a hazard-free working environment. This fix avoided the problem of cutting into the concrete floor of the platform for temporary below-surface installation of the electrical equipment. The junction box that the worker stepped on measured approximately 61/2 inches long by 41/2 inches wide and protruded 31/2 inches above the flat floor surface. The associated metal conduits were installed approximately 11/2 inches above the floor. To relieve paper jams, personnel were required to lean over the floor-mounted electrical equipment, or more likely to step directly onto the boxes and/or conduits. A nearby access door made it likely that the equipment would be stepped on almost immediately upon entering the area of the newspaper handling machinery. A consultant’s plans for the automated newspaper-handling installation called for the locations, including mounting heights of junction boxes and other electrical components, to be reviewed and approved by the purchaser’s staff. This provision was intended to prevent the design and actual construction from violating various codes and standards. However, several drawings showed that boxes and conduits were to be installed directly on the floor surface. Analysis of the causes of this accident included a review of the National Safety Council’s Accident Prevention Manual for Industrial Operations, which states that, “fall-causing hazards include ...stumble hazards...” Falls were considered the second largest cause of accidental death. Many other tripping and stumble hazards are noted in the manual, such as loose material underfoot, in order to emphasize their seriousness. This and similar statements throughout the manual are apparently intended to stress the hazards of falls due to obstructions and improper floor maintenance. Considerable efforts have been made to study and standardize footwear and working floor surfaces in order to reduce falls, which account for 20 percent of all compensable work injuries. The National Electrical Code (NEC) governs requirements for the type of installations involved in the accident. The NEC requires generally that boxes be mounted directly on structural members of a building or on brackets or similar devices that are in turn fastened to structural members. Alternatively, boxes may be mounted or embedded in various types of channels that are installed below a floor surface, with their upper surfaces level with the floor grade. The NEC has no provision for mounting a box or other electrical components directly on a floor surface. If these practices had been followed in this case, the box and conduits would not have served as obstructions and the accident would have been avoided. The specific wording of the 1971 NEC, which governed this installation, was as follows: Article 354-13 and 358-5. Junction boxes shall be leveled to the floor grade and sealed...Article 370-17(b). Floor boxes especially approved for the purpose shall be used for receptacles located in the floor. In addition, NEC Article 348-1 required that electrical metallic tubing not be used where subject to severe physical damage during installation or afterward. NEC Articles 354 and 358 for under-floor raceways provide details of construction methods that avoid above-floor surface-level exposure. Other standards concerned with the safety of electrical equipment related to a walking surface include the National Electrical Safety Code (NESC). Although the NESC in this context is focused specifically on electrical supply stations (e.g., substations, Rules 112 A and B require that floors have even surfaces, and that passageways be unobstructed), OSHA Rules are also concerned with safe flooring. 29 CFR 1910.305(a)(2)(iii)(B) requires that branch circuits not be laid on a floor, and 29 CFR 1910.22(b)(1) specifically prohibits obstructions in aisles at loading docks. In addition to posing a tripping hazard, with the associated prospect of blunt force trauma to a worker, floor-mounted electrical equipment is a potential fire and shock hazard. Particularly in a working environment, there’s the constant possibility that a heavy vehicle, or heavy load that falls while being moved or transported, may press upon and distort or break a metal box or tubing. This can damage, break, or mutilate electrical wiring and insulation and result in a short circuit or energizing of non-current carrying parts of electrical equipment. Accordingly, NEC Rule 110-17(b) requires the employment of enclosures or guards to prevent physical damage. Almost equivalent physical protection is afforded if the equipment does not protrude above a walking surface. MAZER is a consulting electrical engineer specializing in electrical safety issues. His telephone number is (202) 338-0669, and his e-mail address is email@example.com.