The Mine Safety Health Administration (MSHA) issued a Program Policy Letter that was intended to provide guidance for guardrails or other restraint systems. The Policy Letter highlights different requirements based on the elevation profile of the weighbridge of a truck scale.
– If the profile is 16” or less, then standard 8” high guide rails are satisfactory.
– If the profile is greater than 16”, then it must be treated differently.
Several standard offerings for a double-high rail system, with the top rail at 24” above the deck, reaches center-of-axle on a vast majority of over-the-road vehicles, but as the regulation states, “Any guardrail should extend to at least mid-axle height of the largest truck using the scale”. Therefore, it becomes the responsibility of the end user to advise their sales person and the truck scale manufacturer on their actual height requirement based on the largest trucks to be weighed.
Keep in mind that rail systems provided on a typical truck scale are referred to as guide rails or rub rails or sight rails, but definitely not guardrails as MSHA chooses to define them. Therefore, most if not all, scale manufacturers do not claim that any of the guide rail systems attached to truck scales are fully MSHA compliant as there are simply too many application variables identified in the regulation and it really must be evaluated on a case-by-case basis.
Application unknowns such as speed of vehicle and angle of impact are specifically highlighted by MSHA as follows………“There are four parameters that should be considered in designing guardrails for a scale: the height of the rails (impact height); the speed of the vehicle while driving onto, over, or off the scale; the loaded weight of the vehicle; and the angle of impact.” MSHA sums it up quite well in their own wording when they state – “The mine operator should evaluate each of these variables for their operation and design accordingly” and – “There is no “one-size-fits-all” design for guardrails on truck scales”.
When it comes to truck scales with an elevation greater than 16”, the only way a customer is going to comply with all aspects of the MSHA regulation and it’s true intent is to hire a civil or highway engineer to design a proper guardrail system that is connected to the ground and designed to absorb or deflect the vehicle’s kinetic energy. As MSHA states, “….a guardrail at least mid-axle height is intended to prevent the vehicle from driving through or over it.” Some customers are actually choosing to install the type of guardrail system that is commonly found along highways.