trenching and excavations

SUBPART P 1926.650

GA Tech Health and Safety Consultation Program

INTRODUCTION This training information has been prepared by the Safety and Health

Consultation Program at Georgia Tech with the technical collaboration of Mr. Juán C. Rodriguez and under the sponsorship of OSHA. Its content may be copied and distributed for free, and the only request made to the user is that Georgia Tech’s Safety and Health Consultation Program be acknowledged as the source. All information contained in this training is believed to be correct by the authors, but it is important to point out that, this is not an official OSHA publication and has not been revised or approved by OSHA. The user should be aware that the recommendations provided in this training do not replace any OSHA standard or regulation.

Georgia Tech Safety and Health Consultation ProgramGeorgia Tech Research Institute

260 14th Street, Fourth FloorAtlanta, GA 30332-0837

Voice : (404) 407-7431 FAX : (404) 407-8275

Web http//www.oshainfo.gatech.edu Email: [email protected]


Definitions

Cave-in: means the separation of a mass of soil or rock material from the side of an excavation, or the loss of soil from under a trench shield or support system, and its sudden movement into the excavation, either by falling or sliding, in sufficient quantity so that it could entrap, bury, or otherwise injure and immobilize a person


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Definitions

Competent person: means one who is capable of identifying existing and predictable hazards in the surroundings, or working conditions which are unsanitary, hazardous, or dangerous to employees, and who has authorization to take prompt corrective measures to eliminate them


Definitions

Excavation: means any man-made cut, cavity, trench, or depression in an earth surface, formed by earth removal

Hazardous atmosphere: means an atmosphere which by reason of being explosive, flammable, poisonous, corrosive, oxidizing, irritating, oxygen deficient, toxic, or otherwise…


Definitions

…harmful, may cause death, illness, or injury

Ramp: means an inclined walking or working surface that is used to gain access to one point from another, and is constructed from earth or from structural materials such as steel or wood


Definitions

Protective system: means a method of protecting employees from cave-ins, from material that could fall or roll from an excavation face or into an excavation, or from the collapse of adjacent structures. Protective systems include support systems, sloping and benching systems, shield systems, and other systems that provide the necessary protection.


Definitions

Registered Professional Engineer: means a person who is registered as a professional engineer in the state where the work is to be performed. However, a professional engineer, registered in any state is deemed to be a "registered professional engineer" within the meaning of this standard when approving designs for "manufactured protective systems" or "tabulated data" to be used in interstate commerce


Definitions

Tabulated data: means tables and charts approved by a registered professional engineer and used to design and construct a protective system.


Definitions

Trench excavation: means a narrow excavation (in relation to its length) made below the surface of the ground. In general, the depth is greater than the width, but the width of a trench (measured at the bottom) is not greater than 15 feet)


Definitions

Means of access and egress: Structural ramps that are used solely by employees as a means of access or egress from excavations shall be designed by a competent person. A stairway, ladder, ramp or other safe means of egress shall be located in trench excavations that are 4 feet (1.22 m) or more in depth so as to require no more than 25 feet (7.62 m) of lateral travel for employees.


Definitions

Soil classification system: means, for the purpose of this subpart, a method of categorizing soil and rock deposits in a hierarchy of Stable Rock, Type A, Type B, and Type C, in decreasing order of stability. The categories are determined based on an analysis of the properties and performance characteristics of the deposits and the characteristics of the deposits and the environmental conditions of exposure


Definitions

Cohesive soil: means clay (fine grained soil), or soil with a high clay content, which has cohesive strength. Cohesive soil does not crumble, can be excavated with vertical sideslopes, and is plastic when moist. Cohesive soil is hard to break up when dry, and exhibits significant cohesion when submerged. Cohesive soils include clayey silt, sandy clay, silty clay, clay and organic clay


DefinitionsStable Rock: means natural solid mineral material that

can be excavated with vertical sides and will remain intact while exposed

Type A: means cohesive soils with an unconfined, compressive strength of 1.5 ton per square foot or greater. Examples of cohesive soils are: clay, silty clay, sandy clay, clay loam and, in some cases, silty clay loam and sandy clay loam. Cemented soils such as caliche and hardpan are also considered Type A.

However, no soil is Type A if: The soil is fissured; or if

the soil is subject to vibration from heavy traffic, pile driving, or similar effects; or if the soil has been previously disturbed, or if the material is subject to other factors that would require it to be classified as a less stable material


Definitions

Type B: means: Cohesive soil with an unconfined compressive strength greater than 0.5 ton per square foot but less than 1.5 tsf; or granular cohesionless soils including: angular gravel (similar to crushed rock), silt, silt loam, sandy loam and, in some cases, silty clay loam and sandy clay loam. Likewise, classifies as type A soil, previously disturbed soils except those which would otherwise be classed as Type C soil, soil that meets the unconfined compressive strength or cementation requirements for Type A, but is fissured or subject to vibration; or dry rock that is not stable


Definitions

Type C: means cohesive soil with an unconfined compressive strength of 0.5 ton per square foot or less; or granular soils including gravel, sand, and loamy sand; or submerged soil or soil from which water is freely seeping; or submerged rock that is not stable, and in general any soil about which there is not reliable information upon its properties


DefinitionsUnconfined compressive strength: means the

load per unit area at which a soil will fail in compression. It can be determined by laboratory testing, or estimated in the field using a pocket penetrometer, by thumb penetration tests, and other methods.

Distress: means that the soil is in a condition where a cave-in is imminent or is likely to occur. Distress is evidenced by such phenomena as the development of fissures in the face of or adjacent to an open excavation; the subsidence of the edge, the slumping of material from the face, the bulging of material from the bottom of an excavation, etc


Acceptable Visual and Manual TestsVisual Tests: Visual analysis is conducted to determine

qualitative information regarding the excavation site in general, the soil adjacent to the excavation, the soil forming the sides of the open excavation, and the soil taken as samples from excavated material. Observe samples of soil that are excavated and soil in the

sides of the excavation. Estimate the range of particle sizes and the relative amounts of the particle sizes. Soil that is primarily composed of fine-grained material is cohesive material. Soil composed primarily of coarse-grained sand or gravel is granular material

Observe soil as it is excavated. Soil that remains in clumps when excavated is cohesive. Soil that breaks up easily and does not stay in clumps is granular

Observe the area adjacent to the excavation and the excavation itself for evidence of existing utility and other underground structures, and to identify previously disturbed soil


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Pruebas Manuales y Visuales AceptablesPruebas visuales: se realiza un análisis visual para

determinar información cualitativa, relacionada con el sitio de la excavación en general, el suelo que forma los lados de la excavación abierta, y las muestras tomadas de lo extraído Observar las muestras de suelo extraído de la

excavación y del suelo a los lados de la misma: tamaño de las partículas: finas (cohesivo), granulado (no cohesivo)

Observar el suelo a medida que es excavado: terrones (cohesivo), si se quiebra o parte fácilmente y no permanece en terrones (granular)

Buscar evidencia de conexiones de servicios públicos u otras estructuras subterráneas (suelo previamente removido)


Tests...Manual Tests: Manual analysis of soil

samples is conducted to determine quantitative as well as qualitative properties of soil and to provide more information in order to classify soil properly

These analyses include tests of plasticity, thumb penetration, dry strength, and other strength tests (i.e.; using a pocket penetrometer)


Maximum Allowable Slopes

Soil or Rock for excavaciones < 20 feet deep: maximum allowable slopes (H:V):

Stable Rock ….Vertical (90˚)Type A…………….3/4 : 1 (53˚)Type B…………… 1 : 1 (45˚)Type C………….. 1 ½ : 1 (34˚)


Design of Sloping...The slope may be: “maximum allowable slope”, as

determined from Table B-1 of this appendix and is expressed as the ratio of horizontal distance to vertical rise (H : V). Also, it may be “actual slope”, which shall not be steeper than the maximum allowable slope: (1/2 H: 1V)

There are special considerations for short term exposure: means a period of time less than or equal to 24 hours that an excavation is open

Sloping or benching for excavations greater than 20 feet deep shall be designed by a registered professional engineer


TRENCH SHIELDSUnlike timber shoring for trenches or any

other material which is mainly used as a method of protection of the integrity of the sides of an excavation, the use of trench shields (metallic structures also commonly called “boxes”) is for protecting the workers from cave-ins and any other similar incident

Shields shall be installed in a manner to restrict lateral or other hazardous movement of the shield in the event of the application of sudden lateral loads


Trench Shield...

Trench shields or “boxes” are generally used in accordance to the ground slope and the graded bend/edges of the sides of the trench. The upper edges of the vertical sides (top) of a “box” shall extend to a height at least 18 inches above the top of the excavation, except when the sloping of it faces the opposite side of the “box”


Trench Shield...

It may be excavated 2 feet past the lower end of the trench shield, but only if the “box” has been designed to withstand the previously calculated force for the total depth of the trench


Protection from loose rocks or soil from the excavation

Soil and/or any other material excavated shall be placed at least 2 feet from the edge of the excavation and/or protective barricades (retaining devices) shall be installed at intervals on the face of it to stop and contain falling materials or equipment that could pose a hazard to employees working in the trench. Also the excavated material allows for a real measurement of the trench’s depth


Loose soil...

If the materials excavated are not placed at a safe and appropriate distance from the edges of the excavation, they may cause changes of the safety requirements


Workers or vehicles crossing over a trenchIf due to any circumstance, either workers or

vehicles shall circulate/move across a trench then the following conditions shall be implemented:

If it is a vehicle crossing over it, a system designed and supervised by a registered professional engineer shall be used

If it is workers walking over it, then a bridge shall be installed in accordance to the following requirements:


Crossing over...

Shall have a safety factor of 4Shall have a minimum width of 20 inchesShall have a guardrail system installed on

both sides in accordance to the standard Shall extend 2 feet beyond the edges of the

trench


AccessThe access to and egress from any excavation

shall be adequate and safe for workers and require of the following:Trenches more than 4 feet deep shall have

some type of accessThe separation distance between ladders

placed in an excavation shall not be more than 25 feet


Acceso...

Las escaleras deben estár aseguradas, y extenderse un mínimo de 36 pulgadas (.9m) por encima del borde/orilla superior de la excavación

las escaleras de metal deben usarse con precaución, particularmente si hay conexiones de servicios públicos para electricidad


Access...

Ladders shall be secured and the upper ends of their side rails must extend at least 36 inches above the surface of the ground / edge of an excavation

Metal ladders shall be used with caution, particularly if there are electrical public utility connections


Location of underground installations

Keep in mind that there might be underground utility installations to be encountered during excavation work , such as sewer, telephone, fuel, electric, water lines, or any other underground installations. In order to avoid damaging them as well as a personal safety measure, their estimated location shall be determined prior to opening an excavation. Therefore, utility companies, local government (municipal) offices, or owners shall be contacted (call up) and asked to establish the location of the utility underground installations prior to start digging


Hazardous atmospheres / confined spaces

No one shall be allowed to work in hazardous atmospheres such as: Atmospheres containing less than 19.5

percent oxygen or more than 23.5% of oxygen Atmospheres containing a concentration of a

flammable gas in excess of 20 percent of the lower flammable limit of the gas

Atmospheres containing concentrations of hazardous substances and/or atmospheric contaminants which exceed the safe specified limits indicated by the government


Atmospheres...All operations which involve these types of

atmospheres shall comply with the requirements specified by OSHA (Subpart D and E, 29CFR 1926)

Evaluation/testing of an atmosphere:When controls are used that are intended to reduce

the level of atmospheric contaminants to acceptable levels, testing shall be conducted as often as necessary to ensure that the atmosphere remains safe before workers go down to the excavation


Atmospheres...The frequency of the tests shall be incremented

in case that there are operating machinery and equipment, running-gas motors, welding works, or something shall be burned in the working area

In case that the use of proper respiratory protection shall be necessary, workers shall be trained and registered in a respiratory protection program

Some trenches do qualify as confined spaces


Always take into account :HOW MUCH DOES THE SOIL WEIGH?

EMERGENCY RESCUE EQUIPMENT

WATER ACCUMULATION

INSPECTIONS

BIBLIOGRAPHY


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