IRSST - Institut de recherche Robert-Sauvé en santé et en sécurité du travail

Seat belt assemblies for counterbalanced lift trucks – Preliminary study of normative and usability criteria

Summary

Since the coming into force of a new section of Québec’s Regulation respecting occupational health and safety (ROHS), counterbalanced, center control, high-lift trucks with a sit-down, nonelevating operator must be equipped with a restraint device that prevents the operator from being crushed by the truck structure in the event of a tipover. Pelvic restraint belts are one of the most commonly used means of meeting this requirement. Based on the literature, a brief examination of certain types of seat belts sold on the Québec market and maintenance operations, and observations of twelve operators and seven supervisors at seven companies, this exploratory study provides an overview of seat belt use, from two points of view: seat belt performance standards and seat belt usability in the workplace.

In the companies visited, the lift operators had some difficulty accepting the obligation to wear a seat belt. Most of the operators mentioned, however, that over time they had developed the habit of wearing their seat belt. That said, several of them indicated that they found it useless or annoying, mainly because of the truck’s limited speed, the restrictions the belt placed on their physical mobility when travelling in reverse, and above all, because their tasks required them to mount or dismount the truck frequently. Our observations of the operators at work revealed in fact that some of them dismounted their trucks on average every 2.6 minutes. While the the average time it takes to actually fasten the seat belt is only five seconds, this time can increase significantly when there are problems with the strap retractor rewinding system. Other factors, such as poorly attached retractors, straps that are too short, a thigh restraint that hinders fastening the belt, non-optimal buckle placement or buckle attachment hardware, and interference between the strap and the waist tool belt, are factors likely to compromise the seat belt’s acceptability, its ease of use, and operator safety.

Based on the analyses performed in this study, it is not currently possible to recommend a retractor that reconciles the factors of safety, comfort, and compatibility with task-related needs and for every situation. In the field, belts with an automatic locking retractor (ALR) are a frequently installed model. These retractors automatically take up the slack in the strap and prevent it from unwinding at all times. The operators thus have only limited possibilities of moving on their seat, for example, when travelling backwards. When vibrations are present and there are relative movements between the operator and the anchor points of the seat belt, the tightening of the strap can become particularly uncomfortable. Use of an emergency locking retractor (ELR) is an alternative option available on the market. This retractor ensures good operator mobility since, under normal operating conditions, the slack in the strap is automatically taken up by a slight pull exerted by the retractor, yet without activating the strap’s locking mechanism. However, from the point of view of operator safety, while seat belts with ELRs comply with the SAE J386 reference standard applicable to off-road work vehicles, the retractor may not lock in numerous situations involving lift truck tipovers because the acceleration rate of the truck and the operator may be low during such incidents relative to the locking threshold values specified in the standards. Standard SAE J386 is similar in many regards to Technical Standards Document (TSD) number 209, which describes the requirements regarding seat belts used in automobiles in Canada and the United States. However, the kinematics of lift trucks in terms of speed and acceleration differ from those of cars during tipovers or collisions. Lower values for belt locking thresholds might improve the performance of ELRs, depending on the tipover situation. To ensure compliance, such criteria would potentially require the use of new locking mechanisms. A seat belt that separates the vehicle-tilt-sensitive locking threshold from the vehicle-acceleration-sensitive locking threshold would do much to improve ERL performance, provided that the tilt threshold value was limited to between 12 and 15 degrees.

Seat belt assemblies with manual retractors, which require the operators themselves to adjust the length of the strap, offer the advantage of not tightening on the user. Such retractors also appear to offer a good solution in terms of protecting the operator in all situations. However, it is important to ensure that there is relatively little slack in the belt (less than five cm), which may in turn limit the operator’s mobility when he is seeking rearward visibility. This type of belt also requires each new operator who drives the truck to readjust the strap.

When choosing equipment, a large number of managers in companies are interested in devices that facilitate management of seat belt use (e.g. strap colour, a sound-producing warning device activated when the seat belt is not fastened). However, before purchasing equipment, a needs analysis that takes into account the characteristics of the seat, belt, users, and tasks to be performed, could reduce some of the inconveniences associated with seat belt use. Such an analysis should include operator input. This report provides guidelines intended to fuel this reflection process. Seat belt maintenance could also prove important for minimizing malfunctions.

Additional Information

Category: Research Report
Author(s):
Research Project: 0099-6620
Online since: February 20, 2013
Format: Text