Electrical Hazards in Construction

Transcription

1 Electrical Hazards in Construction WELCOME Tim Dawson Presentation developed by Dawson Safety Services Dangers of Electrical Shock Currents above 10 ma* can paralyze or freeze muscles. Currents more than 75 ma can cause a rapid, ineffective heartbeat -- death will occur in a few minutes unless a defibrillator is used 75 ma is not much current a small power drill uses 30 times as much Defibrillator in use * ma = milliampere = 1/1,000 of an ampere Effects of Current on the Body Electrical Safety in the Workplace Ray A Jones, PE 2001 Men Perception Threshold.001 Amps Painful Shock.009 Amps Lock Down Threshold.045 Amps Ventricular Fibrillation.100 Amps 3 Seconds.200 Amps 1 Second Heart Failure.5 Amps Organ Burn and Cell Breakdown 1.5 Amps Women Perception Threshold.0007 Amps Painful Shock.0012 Amps Lock Down Threshold h.045 Amps Ventricular Fibrillation.100 Amps 3 Seconds.200 Amps 1 Second Heart Failure.5 Amps Organ Burn and Cell Breakdown 1.5 Amps 1

2 Resistance and the body The body has a natural defense system The skins break over voltage is 600 volts Why 50 volts? The key to survival is to increase our resistance and decrease our exposure. Typical Resistance of the Human Body and 50 Volts. The typical body has a contact resistance of 500 ohms at the point of contact with the electrical source. The body has an internal resistance of approximately 100 ohms. There is another point of contact to ground of 500 ohms. 120v / ( ) = 110mA 50v / ( ) = 45 ma 45 ma is the lock up threshold. Once lock up occurs, exposure time is increased and the possibility of electrocution may occur. Electrical Safety In the Workplace Ray A. Jones, PE 2001 Electrical Safety Planning at the Jobsite The requirements for electrical safety must be distributed and highlighted as part of the bid package. Contract is awarded and electrical safety requirements must be reviewed again. The Pre-Construction meeting is conducted with all subcontractor superintendents and GC Superintendent; the Project Safety Plan is reviewed. Finally, electrical safety requirements are rigorously enforced, no exceptions (a) Approval All electrical conductors and equipment shall be approved. UNDERWRITERS LABORATORIES LISTED ENCLOSED SWITCH Issue AK

3 403(b)(1) Examination. The employer shall ensure that electrical equipment is free from recognized hazards that are likely to cause death or serious physical harm to employees. Suitability for installation and use in conformity Mechanical strength and durability. Electrical insulation. Heating effects under conditions of use. Arcing effects. Classification by type, size, voltage, current capacity, specific use. Other factors which contribute to the practical safeguarding of employees using or likely to come in contact with the equipment (d)(1) Mounting. Electric equipment shall be firmly secured to the surface on which it is mounted. Wooden plugs driven into holes in masonry, concrete, plaster, or similar materials shall not be used (e) Splices Conductors shall be spliced or joined with splicing devices designed for the use or by brazing, welding, or soldering with a fusible metal or alloy. Soldered splices shall first be so spliced or joined as to be mechanically and electrically secure without solder and then soldered. All splices and joints and the free ends of conductors shall be covered with an insulation equivalent to that of the conductors or with an insulating device designed for the purpose. 3

4 (h) Identification of disconnecting means and circuits. Each service, feeder, and branch circuit, at its disconnecting means or overcurrent device, shall be legibly marked to indicate its purpose, unless located and arranged so the purpose is evident. These markings shall be of sufficient durability to withstand the environment involved. BEFORE IT IS ENERGIZED! MARKINGS (i)(2) Guarding of live parts. (i)(2)(i) Except as required or permitted elsewhere in this subpart, live parts of electric equipment operating at 50 volts or more shall be guarded against accidental contact by cabinets or other forms of enclosures, or by any of the following means: 4

5 (a)(2) Reverse Polarity Neutral Reversed Hot (e)(1)(iv) Location in or on premises. Overcurrent devices shall be readily accessible. Overcurrent devices shall not be located where they could create an employee safety hazard by being exposed to physical damage or located in the vicinity of easily ignitable material (b)(1)(ii) Ground-fault circuit interrupters. All 120-volt, single-phase 15- and 20-ampere receptacle outlets on construction sites, which are not a part of the permanent wiring of the building or structure and which are in use by employees, shall have approved ground-fault circuit interrupters for personnel protection. * The NEC has included the 30 ampere receptacle outlet & receptacles other than 125 volts. (240 volt single phase) Common Name Pig Tail 5

6 (f)(6) Grounding path. The path to ground from circuits, equipment, and enclosures shall be permanent and continuous. Grounding Grounding creates a low- resistance path from a tool to the earth to disperse unwanted current. When a short or lightning occurs, energy flows to the ground, protecting you from electrical shock, injury and death (a)(2)(ii) General requirements for temporary wiring - (C)Receptacles for uses other than temporary lighting shall not be installed on branch circuits which supply temporary lighting. Receptacles shall not be connected to the same ungrounded conductor of multiwire circuits which supply temporary lighting. WHY??? 6

7 Temporary Lighting All lamps for general illumination shall be protected from accidental contact or breakage. Temporary lights shall not be suspended by their electric cords unless cords and lights are designed for this means of suspension. Flexible cords and cables shall be protected from damage. Sharp corners and projections shall be avoided. Flexible cords and cables may pass through doorways or other pinch points, if protection is provided to avoid damage (a)(2)(ii)(J) Extension cord sets used with portable electric tools and appliances shall be of three-wire type and shall be designed for hard or extra-hard usage. Flexible cords used with temporary and portable lights shall be designed for hard or extra-hard usage. NOTE: The National Electrical Code, ANSI/NFPA 70, in Article 400, Table 400-4, lists various types of flexible cords, some of which are noted as being designed for hard or extra-hard usage. Examples of these types of flexible cords include hard service cord (types S, ST, SO, STO) and junior hard service cord (types SJ, SJO, SJT, SJTO). 7

8 (b)Cabinets, boxes, and fittings. (b)(1) Conductors entering boxes, cabinets, or fittings. Conductors entering boxes, cabinets, or fittings shall be protected from abrasion, and openings through which conductors enter shall be effectively closed. Unused openings in cabinets, boxes, and fittings shall also be effectively closed. Hazard - Overhead Power Lines Usually not insulated Examples of equipment that can contact power lines: Crane Ladder Scaffold Backhoe Scissors lift Raised dump truck bed Aluminum paint roller Control - Overhead Power Lines Stay at least 12 feet away (OSHA is 10 Feet) Post warning signs Assume that t lines are energized Use wood or fiberglass ladders, not metal Power line workers need special training & PPE 8

9 Underground Utilities Must be located within 24 hours before works begins. (Recommend: Take a photograph of area after locates are completed.) Flags get moved, have Utility location painted on the ground. Employees must be notified of the utilities they may come in contact with. Portable Generators The frame of the portable generator need not be grounded if: the generator supplies only cord and plug connected equipment. The non-current carrying metal parts of equipment and the equipment grounding conductor terminals of the receptacles are bonded to the generator frame. GFCI is required if >5kV or if generator provides 220V as well as 110V. LOTO - Potential Killer if Ignored (b) Equipment and circuits. Equipment or circuits that are deenergized shall be rendered inoperative and shall have tags attached at all points where such equipment or circuits can be energized. However --- National Electrical Code states --- Locks and Tags! 9

10 Proper Lockout/Tagout TESTERS Verification of Electrical Lockout includes use of non-contact voltage and current testers. If contact testing is required (open panel testing) during lockout procedures, the electrician is required to wear appropriate electrically insulated gloves and instrument leads shall be inspected to ensure insulation is intact. RECOGNITION OF ELECTRICAL HAZARDS EXERCISE 10

11 Yes, This was energized! Can not use romex cable as a flexible cord! 11

12 Access to Electrical Panels 12

13 What could cause a fire? 13

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15 Copper Theft Very dangerous hazard. 15

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17 THE END 17