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Hieber’s Harbor: Saving Space and Lives at Tank Excavations

An innovative way of reducing the tank excavation and backfill required by over 80%. Workers enter the excavation by going over the hazardous area near the excavation walls and they do their work in safety in the "Heiber Harbor".



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Author: Hieber J. Stephen , P.O.E.
An alternative to traditional sloping methods
Despite its obvious merits, the alternative excavation sloping method described in this article has not yet been approved by the Occupational Safety and Health Administration (OSHA) for general use. The author has applied for and hopes to soon obtain such approval. In the meantime, it has been his experience that, under appropriate circumstances and in conjunction with the proper employee training and other safety measures, employers can get OSHA’s approval on a-case-by-case basis. He cautions that the acceptability of the method may vary from state to state and that OSHA should be consulted in advance of employing the method.

Hieber’s Harbor is a proposed method for sloping the walls of an underground tank excavation to provide a worker protection system as required by OSHA regulations (29 CFR Part 1926.650). The OSHA standard defines a protective system as: A method of protecting employees from cave-ins, from material that could fall or roll from an excavation face or into an excavation, or from collapse of adjacent structures. Protective systems include support systems, sloping and benching systems, shield systems and other systems that provide the necessary protection.

In my opinion, a properly installed Hieber’s Harbor qualifies as an other system that provides the necessary protection.

Hieber’s Harbor is predicated on the principle that it is more efficient and economical to remove an employee from an unsafe condition than it is to remove an unsafe condition from the employee. The method utilizes a modified 1:1 sloping technique in conjunction with stanchions (posts) to create a clearly defined safe harbor area in the center of the excavation from which the employee can safely perform his work. Hieber’s Harbor allows the creation of a safe working area where either shoring or traditionally accepted sloping methods are impractical because of surface structures or property lines.

Shoring of a multi-tank excavation, in many cases, is not a viable option for a variety of reasons. These include: the inability to move equipment in to handle materials due to surface structures and property lines; the inability to provide crossbracing that allows for the setting of tanks; the unavailability of manufactured shoring systems for this purpose; and the extreme expense. These reasons all make it more economical to do sloping and backfill replacement.

A normal multiple tank excavation is 32 feet by 32 feet by 12 feet deep. However, providing the same excavation with a 1:1 slope requires a surface area 56 feet by 56 feet. There are very few sites that afford this amount of space. Also, in UST installations, the greatest expense is not in the excavation. Rather, it is in the cost of the backfill material used and its placement.

A proposed method for sloping the walls of an underground tank excavation.

An unsloped excavation (vertical walls) with the dimensions noted in the last paragraph would require removing 455 cubic yards (CY) of material. However, the same size excavation in type B soil (for which the OSHA regulations require a 1:1 slope), would require removing an additional 345 CY of material. This 75 percent increase in the amount of material removed not only increases excavation costs considerably, it also increases the amount of backfill required. In this example the required backfill increases from 305 CY to 650 CY, or by more than 100 percent.

Now let us contrast this example with the Hieber’s Harbor modified sloping method. In this case, only the top four feet of the excavation would be sloped at the 1:1 ratio (see illustration); the bottom eight feet would have essentially vertical sides. The amount of material removed, as well as the amount of backfill required, would be only 40 CY more than if the walls were entirely vertical. This represents a significant savings over a full 1:1 slope.

Subsequent to removal of the first four feet of the excavation on a 1:1 slope, the delineation of the harbor area is established at a distance of eight feet parallel to each sidewall. In the example noted, this would result in a safe harbor area measuring 16 feet by 16 feet, as safe as if the 1:1 slope went all the way to the bottom of the excavation.

The author has found a workable distance from the sidewalls to be eight feet. This means that in maintaining a 1:1 slope for employee safety, the vertical section of the sidewall cannot exceed eight feet in height. Conversely, to increase the area of the harbor, it is necessary to decrease the height of the vertical sidewall.

Due to recently developed anchoring and backfill procedures, the only task requiring an employee to be in a tank excavation is the bedding process. This task is safely and efficiently performed within the confines of Hieber’s Harbor.

A stanchion must then be placed, at a minimum, in each corner of the harbor. The stanchions must then be connected with a warning tape, rope, chain or similar device to clearly delineate the working area.

A competent person must perform the duties of “top person” whenever anyone is in the excavation. It is the responsibility of the “top person” to look for and communicate to the person(s) in the harbor any imminent danger that may become apparent and to ensure no one works outside the confines of the harbor. If for some reason the “top person” must leave visual and audible range of the harbor, all persons must exit the excavation.

It must be emphasized that Hieber’s Harbor is a proposed method and is not an approved method. This method is based on empirical data only at this time. However, based on the preliminary studies conducted by a geotechnical engineer, the author hopes to soon gain approval through the use of tabulated data.

J. Stephen Hieber is president of PWI, Incorporated, a petroleum equipment contracting firm, located in New Oxford, PA.

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