Digging a Safe Trench
Filed Under (Advice, Basic Information) by admin on 03-02-2012
OSHA (Occupational Safety & Health Administration) defines a trench as a “narrow excavation made below the surface of the ground.” In the basement waterproofing industry, the trench is created along the side of an underground foundation wall in order to expose the problem area. A section or all of a foundation that is leaking will be exposed in order to repair it. Waterproofing a foundation by excavating the leaking wall is a very common procedure.
Sadly, many companies do not create safe trench environments and many workers have been badly injured or even killed as a result. The National Institute of Occupational Safety and Health (NIOSH) states that 271 workers died from 2000 to 2006 from trench cave-in accidents.
You can read more about that here.
Because of this problem, OSHA has created strict guidelines to protect workers from harm. The guidelines are as follows:
First, all surface encumbrances must be removed or secured. Once completed, all utility lines need to be clearly marked. In Pennsylvania this is done by calling Pennsylvania One Call System or “PA1 Call” as it is known. Once these utility lines are found, they must be secured as needed to prevent damage or harm to workers.
Establishing the type of soil the trench will be dug in as well as the overall depth are the next key factors to consider. Soil type is important to note as it will dictate how steep the side walls of the trench can safely be. There are three basic soil classifications to understand:
- Type A, which is a cohesive undisturbed soil that is predominately clay.
- Type B soil is angular gravel or predominantly silty soil.
- Type C is predominately sand. Each type of soil has its own maximum allowable slope.
The Maximum Allowable Slope means the steepest incline of an excavation face that is acceptable for the most favorable site conditions as protection against cave-ins, and is expressed
as a ratio of horizontal distance to vertical rise (H:V).
In trenches less than 20 feet deep, Type A soil can have a slope 3/4:1 or 53 degrees, Type B soil can have a slope of 1:1 or 45 degrees and Type C soil can have a maximum slope of 1 1/2:1 or 34 degrees. By following these guidelines trenches will have the greatest chance of not caving in.
The next step is a means of egress. This is a way out of the trench for workers and can be steps, ladders or any other safe means of exit. The next aspect is to provide workers with warning vests should the trench be located near moving traffic or dump trucks to make them more visible to vehicle traffic. If dump trucks are loaded, no worker shall be permitted underneath loads handled or lifted so to prevent falling hazards. Additional information on this section is provided by OSHA Code 1926.601(b)(6) and can be looked up at the www.osha.gov website.
If additional bracing is required (due to increased trench depth) the trench can be outfitted with additional support in the form of “trench shields” or “trench boxes.” These are structures inserted into the trench which can withstand the forces imposed on them by cave-in and thereby protect the worker. Please refer to OSHA Code 1926.652(c)(3) or (c)(4) for additional details.
Once you have created a safe open trench, it is necessary to ensure that it remains safe going forward. Daily inspections, as well as inspections after rainstorms, should be conducted by a competent person prior to work beginning. If the competent person finds evidence of a potential cave-in, they should remove all workers from potential hazard until the conditions are made safe again.
In closing, a safe trench is imperative. Not only are workers lives on the line, but the homeowner you are working for must also be sure they are working with a professional and knowledgeable company.
Should the homeowner hire a company that is operating without Workman’s Compensation Insurance, they could be liable for harm of a worker while on their property. In the end, be sure to double check your contractors’ Workman’s Comp Policy. It is the law that they have such coverage.
At Keystone Basement Systems, we go the extra mile to ensure that ALL guidelines are followed, and safety is of our primary concern.

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