Safety Measures inExcavation and Trenching
Occupational Safety and Health Administration (OSHA) believed that the rate of deaths and serious injuries resulting from trenching and excavation incidents, especially collapses, can be significantly reduced if OSHA concentrates resources to deal with trenching and excavation operations through strict enforcement especially effective and close monitoring activities at construction sites. With this vision, OSHA came up with significant updatesto CPL 02-00-069 - Special Emphasis: Trenching and Excavation, of 1985.
As far as modern protective systems is concerned, OSHA recognizes slope establishment, benching, shoring, and trench shielding/trench boxing as legitimate ways of protecting workers in a trench.
Sloping involves profiling the sides of soil so that the top of the trench is wider than the bottom of the trench. For trenches in Type C soil, OSHA requires 18 inches of width for every 12 inches of depth (53 degrees). For Type B soils, its 12 inches of width for every 12 inches of depth (45 degrees), and for Type A soils, its 9 inches of width for every 12 inches in depth (34 degrees). The stability and condition of sloped soil is however not guaranteed to be permanent during a period of time.
Type A - Examples include: clay, silty clay, sandy clay, and clay loam.
Type B - Granular cohesionless soils (such as angular gravel, similar to crushed rock, silt, silt loam, sandy loam, and, in some cases, silty clay loam and sandy clay loam).
Type C - Granular soils (including gravel, sand, and loamy sand), submerged soil or soil from which water is freely seeping, submerged rock that is not stable, or material in a sloped, layered system where the layers dip into the excavation.
Shielding uses trench shields or trench boxes and is very effective in preventing soil collapses. In this method, it is important to pick the product that is right for each soil type. Trench shields/boxes are composed of two large plates held across by four cross members, and the plates are positioned to extend about 18 inches higher than anything that can cave-in.
Benching is similar to sloping, but instead of the top of the trench wall gradually meeting the bottom of the trench by a straight line, it is a series of “steps” (perhaps 1 foot wide for every foot deep). The trench wall looks like a flight of stairs, which is great for ingress and egress, but it can’t be applied in Type C soils and similarly with slopes, the condition and profile of soil may change in short period due to many factors especially weather.
Shoring uses various support systems including timber, aluminum, and steel to prevent soil and the trench walls from moving. When using this method, walings or vertical shores are distributed throughout the trench and each one stretches the width of the trench. The ultimate purpose of shoring is to prevent cave-ins by making sure trench walls are supported at all times and will not collapse.
In brief, the shoring/strutting system consists of tubes or H beams as compression struts, and H beams as a waling to redistribute the horizontal forces over the struts.One example of a shoring product is ESC’s Shoring/Strutting Systems. ESC has experience both designing, supplying and installing shoring/strutting systems in various configurations and project conditions. They can deliver completely customized strutting systems including all necessary prefabricated components. Further product information can be found in www.esctrenchshoring.com.
Proper selection of materials and systems to employ for a job might be critical in preventing incidents, but the main key to a safe and healthful work environment is still a comprehensive injury and illness prevention program with management leadership, worker participation, hazard identification, hazard prevention and control, education and training, and program evaluation & improvement.
For trench shoring solutions, ESC has wide range of products to choose from including but not limited to the Standard Trench Shield, Manhole Trench Shield, and Adjustable Trench Shield. There are also various spreader solutions including telescopic spreaders. ESC shoring systems have been relied on by Contractors for over 30 years, and the trench shield range is one of their most utilized products.