Construction Safety

UnitV.pdf

Home >Engineering homework help >Construction Safety

Course Learning Outcomes for Unit

Upon completion of this unit, students should be able to:

2. Apply Occupational Safety and Health Administration standards and related practices to construction. 2.1 Identify types of welding and related hazards on a construction site. 2.2 Identify electrical safety standards and work practices. 2.3 Identify standards and work practices for safe use of scaffolds. 2.4 Identify the requirements for design and use of stairs and ladders on construction sites.

4. Examine methods used to control common construction hazards. 4.1 Analyze hazards that contribute to construction accidents.

Course/Unit Learning Outcomes

Learning Activity

2.1 Unit V Lesson Required Readings Unit V Assessment

2.2 Unit V Lesson Required Readings Unit V Assessment

2.3 Unit V Lesson Required Readings Unit V Assessment

2.4 Unit V Lesson Required Readings Unit V Assessment

4.1

Unit V Lesson Required Readings Unit V Assessment Unit V Assignment

Reading Assignment

Click here to access the OSHA Construction Industry Digest and read the sections indicated below.

Occupational Safety & Health Administration. (2014). Construction industry digest [Brochure]. Retrieved from https://www.osha.gov/Publications/osha2202.pdf

- Electrical Installations, pp. 18-19 - Electrical Work Practices, pp.19-20 - Ladders, pp. 38-39 - Scaffolds, General Requirements, pp. 52-57 - Stairs, pp. 58-60 - Welding, Cutting, and Heating, pp. 65-66

Occupational Safety & Health Administration. (n.d.). Electrical Safety [PowerPoint presentation]. Retrieved from https://www.osha.gov/harwoodgrants/grantmaterials/fy2009/sh-19504-09

UNIT STUDY GUIDE

Welding and Electrical Safety, Scaffolds, Ladders, and Stairs

https://www.osha.gov/Publications/osha2202.pdf

https://www.osha.gov/harwoodgrants/grantmaterials/fy2009/sh-19504-09

UNIT x STUDY GUIDE

Title Occupational Safety & Health Administration. (n.d.). Scaffolds [PowerPoint presentation]. Retrieved from

https://www.osha.gov/dte/outreach/construction_generalindustry/const_outreach_tp.html

Occupational Safety & Health Administration. (n.d.). Stairways and ladders [PowerPoint presentation], slides 1-13. Retrieved from https://www.osha.gov/dte/outreach/construction_generalindustry/const_outreach_tp.html

Occupational Safety & Health Administration. (n.d.). OSHA fact sheet: Controlling hazardous fume and gases during welding [Fact sheet]. Retrieved from https://www.osha.gov/Publications/OSHA_FS- 3647_Welding.pdf

Unit Lesson

In this unit, we continue our investigation of the hazards common to many construction projects.

Welding and Cutting

Installation and modification of pipes and steel structures and cutting of metals are common tasks in construction. These tasks rely upon high temperatures to melt metal. The most common types of welding and cutting use gas or electricity to generate the high temperatures necessary. Gas welding uses a mixture of flammable gas and oxygen to create a flame and is often used for welding iron, steel, cast iron, and copper (Occupational Safety and Health Administration [OSHA], n.d.-b). Tungsten inert gas (TIG) welding is a common type of arc welding. TIG welding uses an electric arc to heat metals and an inert gas such as helium to shield the weld area from air. Fire and burns are two of the more obvious hazards associated with all welding. In addition, each type also has its own specific hazards that must be controlled. The fuel and oxygen for gas welding are supplied in compressed gas cylinders. The cylinders, whether full or empty, must be handled and stored to prevent damage. Similarly, the inert gas used in TIG welding must be handled and stored safely. Fuel gases and oxygen must be stored in separate areas (OSHA, 1993). TIG welding equipment must be properly grounded; cables, connectors, and electrode holders must be adequately insulated to prevent worker contact with the high levels of electric current used.

Regardless of the process used, the high temperature needed to weld metals generates a wide variety of air contaminants that can be hazardous to the workers using the welding equipment as well as workers in the vicinity of the welding operations. There are many factors that impact the level of hazard to which workers can be exposed (OSHA, n.d.-b):

(Almeida, n.d.)

https://www.osha.gov/dte/outreach/construction_generalindustry/const_outreach_tp.html

https://www.osha.gov/Publications/OSHA_FS-3647_Welding.pdf

UNIT x STUDY GUIDE

Title  type of welding process,

 base metal and filler metals used,

 welding rod composition,

 location (outside, enclosed space),

 welder work practices,

 air movement, and

 use of ventilation controls.

Each welding operation must be evaluated and a determination made on the type of respiratory protection and other PPE that may be required.

Electrical Safety

OSHA has listed electrocutions as one of the construction industry’s “Fatal Four,” accounting for nearly 9% of construction fatalities (OSHA, n.d.-a). If you tour a construction site, you are likely to find many standards violations and unsafe practices in the installation and use of temporary wiring, electric power tools, and flexible extension cords. Electrical shock due to inadequate grounding is a common occurrence. There are two ways to comply with the OSHA requirements for grounding temporary electrical installations: Provide and use ground fault circuit interrupters (GFCIs), or use an assured equipment grounding conductor program.

A GFCI is a portable, fast-acting circuit breaker that detects small circuit imbalances and can interrupt the power in as little time as 1/40 of a second (Johnson, 2013). An assured grounding conductor program is a written program developed by the employer and includes the elements listed below(OSHA, n.d.-b):

 a competent person to administer the program;

 daily visual inspections of equipment and cords;

 continuity tests of the equipment, grounding conductors, receptacles, and extension cords every three months; and

 documentation of all inspections and tests.

Using GFCIs will protect employees and is certainly easier to do, but it will not uncover damage and defects in equipment that can result in lost productivity and additional expense. If a piece of equipment keeps tripping a GFCI and no action is taken to identify and remedy the electrical fault, workers are more likely to stop using the GFCI. Inspections and testing are a best practice for the construction industry and should be part of any electrical safety effort.

Click on the image below for practice in identifying electrical hazards.

It is important to take electricity seriously. It is also important to understand a little bit about the properties of

electricity and electrical circuits to understand how a person might become electrocuted.

There are three characteristics of electricity that are good to know if one is to have a full appreciation of how electricity works. These include voltage, resistance, and amperage. Using water flow as an analogy, voltage

https://online.waldorf.edu/CSU_Content/Waldorf_Content/ZULU/EmergencyServices/OSH/OSH3401/W15Ec/UnitV_LessonActivity.ppsx

UNIT x STUDY GUIDE

Title works a bit like pressure in a water line. The key difference is that, rather than being the force that drives water molecules through a pipe, voltage drives electrons through a conductor.

Keep in mind that the number of electrons flowing through a conductor can be hampered by other parameters, such as the size of the conductor and how much resistance there is in the conductor. Given our water analogy, a lot of pressure in a very small pipe will limit how much water can flow. Likewise, numerous bends in the pipe, bottlenecks, and the smoothness of the inside of the pipe can impact flow as well. Indeed, pipe smoothness, bottlenecks, and number of bends create resistance in a water pipe.

Resistance from an electrical perspective is measured in ohms (Ω). Basically, some materials conduct electricity better than others. Metals such as gold, aluminum, and copper are good conductors. The latter two are frequently used in electrical wiring because of this property. Materials like wood and rubber, however, do not conduct electricity well. They are resistant. Often, resistors are purposely included in circuits to control current and to keep from overloading a circuit.

Current is another important characteristic of electricity that needs to be considered. It is often designated with the letter I. Current is measured in amperes (or amps or A for short) and basically reflects how much

electricity is flowing through a circuit. Actually, amperes are the main concern when it comes to electrocution because the amount of current is what causes electrocutions—as can be seen below.

Going back to our water line analogy, it is apparent that the amount of water flow is also related to the diameter of the line and the pressure. Likewise, amps are related to resistance and voltage according to the basic formula below.

 amps = voltage/resistance or A = V/Ω

Considering this simple relationship, let’s do a simple problem.

Suppose a circuit has a voltage of X volts (V) and a resistance of Y ohms (Ω). Would the amperes be sufficient to kill a person?

Using our equation above, which is an algebraically rearranged version of Ohm’s law, how many amps would flow through a toaster plugged into a 120 V circuit with a resistance of 25 Ω?

Effects of electrical current in the human body (Fowler & Miles, 2009)

(Fowler & Miles, 2009)

UNIT x STUDY GUIDE

Title Our answer to this problem would be A = 120/25, which would be 4.8 A. This would be 4,800 milliamperes (mA) and would result in death.

Other arrangements of the formula above are as follows:

 voltage = amps X ohms or V = A ● Ω

 ohms = voltage/amps or Ω = V/A

Electrical Circuits

Now that we have some familiarity with Ohm’s law, let’s consider another aspect of electrical circuits that relates specifically to resistance. You will note that a given electrical circuit often runs more than one item, and the resistance from each item on the circuit subsequently needs to be considered.

Also, there are two configurations for electrical circuits. The first configuration is a series circuit. Generally, this means that the resistance sources (e.g., light bulbs) are in a linear series along the circuit. A lot of old- fashioned Christmas light strands were wired in a series, and since the electricity completing the circuit had to flow through each bulb, when one bulb burned out, the entire strand would go out.

Below is a diagram of a series circuit where R represents resistance points (e.g., light bulbs).

In a series circuit, resistance is cumulative; therefore, R (total) = R1 + R2 + R3. Thus, if the following is true…

 R1 = 3 Ω

 R2 = 2.5 Ω, and

 R3 = 3.5 Ω

…the total would be 3 + 2.5 + 3.5 = 9 Ω of total resistance.

Parallel circuits are a bit different, however, and are designed to make sure electricity is constantly supplied to all of the items in a given circuit—even if one stops working. Below is a diagram of a parallel circuit.

UNIT x STUDY GUIDE

Title

Again, let’s consider each resistance source (R1, R2, and R3)—a bulb for simplicity’s sake (they can also be motors, blenders, machines, etc.). Note, in this case, that even if one of the bulbs goes out, the electricity will still find its way back to the electrical source through the other pathways, and the circuit would be complete.

Total resistance, however, is added differently for parallel circuits. The formula for calculating cumulative resistance in a parallel circuit is shown below.

So, for a situation where we have the elements listed below…

 R1 = 3 Ω

 R2 = 2.5 Ω, and

 R3 = 3.5 Ω,

…we would end up with the equation below.

 1/R(total) = 1/3 + 1/2.5 + 1/3.5

 1/R(total) = .33 + .4 + .29

 1/R(total) = 1.02 Ω-1.

Taking the inverse of both sides, we get R(total) = 0.98 Ω.

Given this information, if we know the amperage of the power source and the resistance, we can figure out the circuit amperage. If we know the amperage, we can figure out the voltage. If we either know or calculate the amperage, we can determine if there is a significant electric shock hazard. In addition, if you refer back to the table presented above, it does not take very many amps to stop a heart from beating.

I hope that an understanding of electrical hazards and a basic understanding of electrical fundamentals will help to provide you with some foundations for you to build upon as a safety professional. Electric shock hazards are very serious issues to contend with at construction sites. It is good to have a solid understanding of electrical hazards—especially when working at construction sites where you have multiple trades running a wide variety of electrical tools.

Scaffolds

Scaffolds are the most frequently used elevated work platform in construction. Falls represent 36% of construction fatalities, and unsafe scaffolds are a major contributor to this statistic (OSHA, n.d.-a). Additional hazards include bad planking, scaffold collapse, tools or debris falling from the platform, and electrocution (contact with power lines). Scaffolds can be supported from below by load-bearing poles and legs and frames, or suspended from above by ropes and cables. Truck-mounted aerial lifts are also classified as scaffolds (OSHA, n.d.-c). Regardless of the type, some specific rules govern the use of all scaffolds:

 Competent person is required for erection, moving, dismantling, and inspection

 Employees must be trained on safe scaffold use

 Guardrails or personal fall arrest systems required if more than 10 ft. high

 Scaffold platform must be fully planked

 Safe access to scaffold platforms must be provided (OSHA, 2014)

Stairs and Ladders

Like scaffolds, unsafe or improper use of stairs and ladders is a significant factor in fatal falls in construction. As construction (or demolition) progresses, worksite elevations change. Workers must be provided safe access to all levels on a construction site. A stairway or ladder must be provided at any point of access where there is an elevation break of 19 inches or more (OSHA, 2014). Stairways with four or more risers must have

Formula for calculating cumulative resistance

UNIT x STUDY GUIDE

Title at least one handrail. Open sides of stairs must be protected by a stair rail (which includes a mid-rail or screen), and open landings and platforms must be protected by a guardrail.

Portable ladders present a significant challenge to the safety professional. Sometimes, objects and structures on construction sites are mistaken for ladders. Pallets, boxes, inverted paint buckets, and even heavy equipment have been known to look like ladders to some workers. Even when ladders are identified correctly, they are not always inspected for damage or defects, or they are used incorrectly. Stepladders are used as access ladders, workers stand on the top step of a stepladder, straight ladders are not long enough to safely access a rooftop, ladders are not secured, metal ladders are used around energized power lines, and workers carry heavy tools and materials up and down ladders. Some basic rules, such as the ones listed below, can reduce the risk of falls from ladders (OSHA, n.d.-d):

 ladder inspection by a competent person,

 use of the correct ladder for the job,

 use of the correct angle and supports,

 not overloading, and

 training workers in safe ladder use.

For scaffolds, stairs, and ladders, if it is not possible to install guardrails to protect employees from falls, then personal fall arrest systems must be used. These devices will be coved in greater detail in Unit VIII.

References

Almeida, A. (n.d.). Arnaldo Almeida's safe cartoons [Image]. Retrieved from http://www.almeidacartoons.com/Safe_toons1.html

Johnson, D. (2013). DeWALT construction safety and OSHA handbook. Clifton Park, NY: Delmar.

National Institute of Occupational Safety and Health. (2009). Electrical safety: Safety and health for electrical trades: Student manual (Rev. ed.). Retrieved from https://www.cdc.gov/niosh/docs/2009- 113/pdfs/2009-113.pdf

Occupational Safety and Health Administration. (n.d.-a). Commonly used statistics. Retrieved from https://www.osha.gov/oshstats/commonstats.html

Occupational Safety and Health Administration. (n.d.-b). Controlling hazardous fume and gases during welding. Retrieved from https://www.osha.gov/Publications/OSHA_FS-3647_Welding.pdf

Occupational Safety and Health Administration. (n.d.-c). Scaffolds [PowerPoint slides]. Retrieved from https://www.osha.gov/dte/outreach/construction_generalindustry/const_outreach_tp.html

Occupational Safety and Health Administration. (n.d.-d). Stairways and ladders [PowerPoint slides]. Retrieved from https://www.osha.gov/dte/outreach/construction_generalindustry/const_outreach_tp.html

Occupational Safety and Health Administration. (1993). Gas welding and cutting. Retrieved from https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=10696

Occupational Safety and Health Administration. (2014). Construction industry digest. Retrieved from https://www.osha.gov/Publications/osha2202.pdf