ASP Exam Expectations
The Associate Safety Professional exam will generally contain 2 – 4 questions covering the topics of excavation and trenching safety. Soil types, sloping / benching requirements, atmospheric testing, and means of egress appear to be the most frequent exam questions in this subject.
OSHA defines an excavation as any man-made cut, cavity, trench, or depression in the Earth’s surface formed by earth removal, whether by hand or equipment. A trench is defined as a narrow excavation (in relation to its length) made below the surface of the ground. In general, the depth of a trench is greater than its width, but the width of a trench (measured at the bottom) is not greater than 15 feet (4.6 m).
Many of the methods of compliance with regulatory standards generally require a competent person to classify the soil type in an excavation to determine appropriate protection measures. These soil types include:
- Stable Rock – Natural solid mineral matter that can be excavated with vertical sides and remain intact while exposed.
- Type A Soil – Cohesive soils with an unconfined compressive strength of 1.5 tons per square foot (tsf) (144 kPa) or greater. Examples include: clay, silty clay, sandy clay, and clay loam. Certain conditions preclude soil from being classified as Type A. For example, no soil is Type A if it is fissured or has been previously disturbed.
- Type B Soil – Includes cohesive soil with an unconfined compressive strength greater than 0.5 tsf (48 kPa) but less than 1.5 tsf (144 kPa) and 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 Soil – Cohesive soil with an unconfined compressive strength of 0.5 tsf (48 kPa) or less, 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 or with a slope of four horizontal to one vertical (4H:1V) or steeper.
Competent Person – an individual, designated by the employer, who is capable of identifying existing and predictable hazards in the surroundings or working conditions which are unsanitary, hazardous or dangerous to workers, and who is authorized to take prompt corrective measures to eliminate them. Under the OSHA standards for excavation, a competent person is responsible for classifying soil systems, inspecting the excavation site and protective measures, designing structural ramps, and monitoring water removal systems.
Avoiding Underground Utilities
Employers are required to avoid striking underground utilities while excavating. This can be accomplished by determining the locations of utilities prior to digging (Generally this can be accomplished through the use of “811” or “One-Call” procedures). Excavators should determine the exact location of underground utilities by safe and acceptable means (hand digging, probing, hydro-excavation, etc.) when using equipment in the area.
Sloping and Benching
Prior to entering an excavation, all hazards must be accounted for through inspection by a competent person. Common protective methods include sloping, benching, or shoring the sidewalls of an excavation. While excavations in stable rock or those less than 5 feet in depth can be entered with vertical walls, excavations greater than 5 feet deep with Type A, B, or C soil should be sloped or benched to an angle of 3/4:1, 1:1, or 1 1/2: 1 respectively. In addition, the excavation should be inspected by a competent person who deems that there is no potential for cave-in. Excavations should be inspected before being entered, at the start of each work shift or after each work break, and after any event that could alter the status of the excavation. Other protective measures include:
- Storing spoils at least 2 feet from the edge of the excavation
- Provide a warning system along the edge of the excavation when equipment will operate in the vicinity or approach the edge without a clear view.
- Protect workers from loose materials along the edge or sides of the excavation by stabilizing or removal
- Not allow workers to work above other workers around an excavation
- Not allow workers to stand or work under loads being moved by excavation or other equipment
- Stand away from vehicles being loaded or unloaded.
Shoring is the provision of a support system for trench faces used to prevent movement of soil, underground utilities, roadways, and foundations. Shoring or shielding is used when the location or depth of the cut makes sloping back to the maximum allowable slope impractical. Shoring systems consist of posts, wales, struts, and sheeting. There are two basic types of shoring, timber and aluminum hydraulic. Most shoring today is hydraulic because workers do not need to enter the excavation for installation. Hydraulic shoring is also lightweight and can be manipulated by one person.
Trench boxes are a type of pre-fabricated shielding system often composed of steel or concrete which is typically lowered into a trench using heavy equipment. The top of the trench box should protrude 18 inches above the excavation. Trench boxes can often be stacked for deeper excavations and may be used in combination with sloping, provided the slope is appropriate for the soil type.
Water in an Excavation
Water in an excavation can undermine the sides of the excavation and make it more difficult for workers to get out of the excavation. The OSHA standards prohibit employers from allowing workers to enter an excavation where water has accumulated or is accumulating unless adequate precautions are taken to protect workers. Such precautions can include special support or shield systems to prevent cave-ins, water removal to control the water level, or the use of a safety harness and lifeline.
If an employer uses water removal equipment to control or prevent water accumulation, the equipment and operations must be monitored by a competent person to ensure proper use. If excavation work interrupts the natural drainage of surface water, the OSHA standards also require the use of diversion ditches, dikes, or other suitable means to prevent surface water from entering the excavation and to provide adequate drainage of the adjacent area. In addition, a competent person must inspect excavations subject to runoffs from heavy rains, and excavations subject to such runoffs are subject to the requirements described previously in this paragraph.
Atmospheric testing is required before workers can enter an excavation greater than 4 feet in depth where an oxygen deficient or hazardous atmosphere could reasonably be expected to be present. If hazardous atmospheric conditions exist or may reasonably be expected to develop in an excavation, the employer must ensure the ready availability of emergency rescue equipment, such as breathing apparatus, a safety harness and line, or a basket stretcher. This equipment must be attended when in use. Note that the Confined Spaces in Construction standard also applies to confined spaces in an excavation.
Means of Egress
OSHA requires employers to provide ladders, steps, ramps, or other safe means of egress for workers working in trench excavations 4 feet (1.22 meters) or deeper. The means of egress must be located so as not to require workers to travel more than 25 feet (7.62 meters) laterally within the trench. Any structural ramps used solely for worker access or egress must be designed by a competent person. Structural ramps used for access or egress of equipment must be designed by a competent person qualified in structural design. Also, structural members used for ramps or runways must be uniform in thickness and joined in a manner to prevent tripping or displacement.