Page 73 - Occupational Health & Safety, July 2017

use of shields. Since the soil was a mixture of class B and C soils, the soil should have been classified as class C soil. Trench ex- cavation with class C soil requires sloping at 11⁄2 H:1V (or 34°), meaning that the soil needed to be cut back 1.5 feet for every 1 foot of depth (Figure 3). Given the proxim- ityofthetrenchtotheconcretewall,itwas impossible to achieve the necessary slope on both sides of the trench. Since the con- crete wall made conventional sloping tech- niques impossible, a trench box or shoring system should have been installed prior to allowing entry into the trench.
The excavation operator commented that he was to bench the road-facing side of the trench. However, OSHA requires that type C soil be sloped and never benched. Fur- thermore, sloping and benching techniques must be applied to both sides of the trench to be effective. The side of the trench facing the concrete wall was the side that was most unstable and suffered the fatal collapse.
monitors allow the excavator operator to monitor the depth and grade from the safe- ty of the operator’s cab. The monitors dis- play highly accurate calculations and often eliminate the need for an operator assistant to check trench grade and/or depth. Mod- ern excavator depth monitors are wireless, requireminimalinstallation,andcanbe moved between machines.
Employers and site managers should ensure employees working in trenches 5 feet or more in depth are protected from cave-in by adequate protection systems appropriate for the conditions in the trench, including sloping or benching techniques, shoring, or shields (trench boxes).1 Sloping involves making sure that the soil is at an angle to prevent the soil from caving into the trench. In this particular incident, sloping was not a viable option due to the proximity of the trench to the adjacent concrete wall. When sloping methods are not feasible, trench shields or aluminum hydraulic shoring sys- tems should be used. In addition to the use of correct protective systems, the spoil pile should also be at least 2 feet from the edge of the trench.
When installing miles of pipeline or cable, the amount of soil that must be moved along with the associated cost of excavator fuel, operator time, backfill, compaction, etc., can make sloping inef- ficient and time consuming in regard to project deadlines. Rather than foregoing the use of a protective system altogether, it is strongly recommended that employ- ers at least require trench shields or alu- minum hydraulic shoring systems, both of which are OSHA-approved protective sys- tems that can be rented, if needed. These protective systems can still adequately protect workers while increasing project expediency and efficiency.
Employers should ensure a competent person conducts soil testing and daily in- spections of the excavations, adjacent ar- eas, and protective systems. A competent person is defined by OSHA 1926.650(b) as “a person capable of identifying existing and predictable hazards in the surround- ings, or working conditions which are unsanitary, hazardous, or dangerous to employees, and who has authorization to take prompt corrective measures to elimi- nate the hazards.”2 Inspections should oc- cur throughout the day and as conditions change. The competent person on the job site was the superintendent who did not
perform a soil test or inspection of the work area prior to allowing work to begin. This was important because the stability of the soil was affected by seven straight days of rain prior to the fatal incident. An adequate soil test should have taken into account that the soil near the concrete wall’s foundation had been previously disturbed, increasing the likelihood of a trench collapse and increasing the need for a required trench protection system.3 The employer had a digital tool to identify soil classification, however, the tool was not used on the day of the incident.
Daily toolbox talks should be conduct- ed that emphasize safety topics related to the upcoming job tasks prior to allowing work to begin on the job site. Pre-work meetings were held before the start of the workday. During the meetings, gen- eral safety hazards were discussed; trench safety was not discussed.
Employers should intervene when un- safe acts on the job site are witnessed. Dur- ing the investigation and interview pro- cess it was discovered that the victim had climbed into and out of the unprotected trench several times that morning. Su- perintendents and other site management personnel should intervene when they witness unsafe job practices.
Safe means of ingress and egress should be provided in all excavations prior to entry. The fatality investigation found no ladder or other safe means of ingress or egress in the trench. OSHA regulations require safe egress and ingress in a trench measuring greater than 4 feet in depth.3 Acceptable means of ingress and egress include lad- ders, steps, and ramps.
De Anna McIntosh is the Case Investiga- tor for the Kentucky Fatality Assessment & Control Evaluation (FACE) Program in KIPRC. References are available in the on- line version of this article, which does not represent final determinations regarding the nature of the incident, cause of the in- jury, or fault of employer, employee, or any party involved. Kentucky FACE is grant funded by grant 2U60OH008483-12 from the National Institute for Occupational Safety and Health and operates from the Kentucky Injury Prevention and Research Center (KIPRC) at the University of Ken- tucky. KIPRC is a bona fide agent for the Kentucky Department for Public Health, http://www.mc.uky.edu/kiprc/.
Vertical
Type C Soil
1 1/2:1
34 degrees
Horizontal
OSHA Sloping Requirements
Soil Type
Slope
Angle (degrees)
A
3/4H:1V
53o
B
1H:1V
45o
C
1 1/2H:1V
34o
Figure 3. OSHA sloping requirements for type C soil. This method would not have been possible due to the proximity of the trench to the concrete wall.
The soil along the concrete wall facing the side of the trench was a mixture of class B and class C soil, along with #57 gravel backfilled along the wall foundation. The soil surrounding the base of the concrete wall had previously been disturbed during the wall’s construction. The spoil pile was placed on the road-facing side of the trench at the required 2 foot minimum distance, however, this was still unsafe due to the pile’s size and the lack of a trench protec- tion system.
Recommendations and Discussion
Alternative methods for measuring trench grade and depth (that do not require an em- ployee to enter the trench) should be utilized, including measuring rulers or poles and excavator depth monitors. Excavator depth
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JULY 2017 | Occupational Health & Safety 69