Excavation Safety 29 CFR 1926.650
Excavation "Excavation" means any man-made cut, cavity, trench, or depression in an earth surface, formed by earth removal.
Trench A narrow underground excavation that is deeper than it’s width but not wider than 4.5 m (Measured at the bottom)
Points to be considered before excavation…. 1. What types of soil will be found? 2. What are the soil moisture conditions? 3. Has the soil previously been disturbed? 4. How large will the excavation be? 5. How long will the excavation be open? 6. What kinds of weather can we expect? 7. What kinds of equipment will be on the job? 8. Will the excavation be near structures? 9. Is traffic control needed near the excavation? 10. What sources of vibration will be nearby? 11. Will water be a problem? 12. What kind of shoring? How much? 13. Underground installations?
Types of Excavation There are 2 types of excavation, • Normal excavation - <1.2 m (or) 6 ft • Deep excavation - >1.2 m (or) 6 ft
Hazards of Excavation • Excavation falling onto man (Cave in). • Man falling into excavation. • Vehicle falling into excavation. • Underground electrical cables and utility lines. • Exposure to toxic, irritating (or) flammable gases. • Confined spaces. • Water accumulation. • Oxygen deficiency.
Prior To Excavation • Ground / Soil condition • Ground / Surface Water • Location of Water Table • Under ground / Overhead utilities • Proximity & physical condition of Adjacent buildings • Dynamic load / Traffic
Soil Classification • Type A – Clay • Compressive Strength of 143.69 kN / M2. or greater. • Type B – Granular Soil • Compressive Strength between 47.91 – 143.69 kN / M2 • Type C – Gravel • Compressive Strength of 47.91 kN / M2 or lesser
Preventing Soil Collapse • Shoring & Timbering • Sheet Piling • Sloping & Benching • Placing a shield.
Shoring & Timbering • Required in trenches • in soil of more than 1.5 m deep • in unstable rock of more than 2 m deep • Vertical sides should extend 30 cm above pit • Approved quality of wood or material of higher strength.
Simple Sloping -Type A Soil • Unsupported vertically sided lower portion < 8 ft
Simple Sloping -Type A Soil • Unsupported vertically sided lower portion < 12 ft
Simple Sloping – Type A Soil • Stable Rock – 900 • Type A – 3/4:1 – 530 • Note :Greater than 20 feet deep shall be designed by a registered professional engineer.
Simple Sloping – Type A Soil • Type B - 1:1 450 Type C - 1½ :1 340
Excavation Safety • Before starting excavation soil condition should be checked. • Before starting the excavation clearance from utilities department must be obtained regarding the presence of UG lines such as Electric, Gas, Sewer, Communications etc.,
Excavation Safety • A safe means of ingress & egress must be provided in excavations that are 4 feet (1.2m) depth. • Maximum distance between ladders must be 25 feet (7.62m) • Employees exposed to vehicular traffic must wear reflective jackets. • Employees are not allowed to stand under the suspended loads.
Excavation Safety • For excavations more than 4 feet (1.22m) depth a confined space entry permit must be obtained & a gas testing prior to entry must be made. • Minimum of 19.5 % Oxygen must be present in excavations. • For atmospheres less than 19.5 % oxygen, all employees must be provided with proper respiratory protection & Ventilation systems.
Excavation Safety • All the excavated materials must be kept at least 2m away from the excavation. • Heavy vehicle movement are not allowed within 2m of excavation.