ACCIDENT PREVENTION STRATEGIES FOR AND BY MANAGERS AND SUPERVISORS

MEANS OF ACCIDENT PREVENTION THAT CAN BE INITIATED BY MANAGERS

As a Manager, there are means and ways that can prevent accidents that you may initiate.

Means of preventing accidents

Strategies for preventing accidents take many forms. These include:

1. Prohibition: Some processes and practices may be so inherently dangerous that the only way to prevent accidents is by management placing a total prohibition on that activity. This may take the form of a prohibition on the use of a particular substance, such as an identified toxic substance, or of prohibiting people from carrying out unsafe practices, such as riding on the tines of a fork-lift truck, climbing over moving conveyors or working on roofs without crawlboards.

2. Substitution: The substitution of a less dangerous material or system of work will, in many cases, reduce accident potential. Typical examples are the introduction of remote control handling facilities for direct manual handling operations, the substitution of toluene, a much safer substance, for benzene, and the use of non-asbestos substitutes for boiler and pipe lagging.

3. Change of process: Design or process engineering can usually change a process to ensure better operator protection. Safety aspects of new systems should be considered in the early stages of projects.

4. Process control: This can be achieved through the isolation of a particular process, the use of ‘permit to work’ systems, mechanical or remote control handling systems, restriction of certain operations to highly trained and competent operators, and the introduction of dust and fume arrestment plant.

5. Safe systems of work: Formally designated safe systems of work, with high levels of training, supervision and control, are an important strategy in accident prevention (see below).

6. Personal protective equipment: This entails the provision of items such as safety boots, goggles, aprons, gloves, etc, but is limited in its application as a safety strategy

Safe systems of work

A safe system of work is defined as ‘the integration of men, machinery and materials in the correct environment to provide the safest possible working conditions in a particular working area’.

A safe system of work should incorporate the following features:

(a) a correct sequence of operations;

(b) a safe working area layout;

(c) a controlled environment in terms of temperature, lighting, ventilation, dust control, humidity control, sound pressure levels and radiation hazards; and

(d) clear specification of safe practices and procedures for the task in question.

Safe systems of work are generally designed through the technique of ‘job safety analysis’.

POWER SYSTEM PROTECTION COORDINATION AND SAFETY ENGINEERING

THE IMPORTANCE OF SYSTEM PROTECTION COORDINATION WITH REGARDS TO PERSONNEL SAFETY

How system protection coordination serve its safety purpose?



System protection coordination
When an electrical distribution system is designed and constructed, a fault-current coordination study should be conducted, and circuit protective devices should be sized and set according to the results of the study.

In time, however, the electrical system configurations are often changed due to the changing needs of the end users. If the coordination and capability of the electrical equipment are not reviewed at the time of the changes, faults could result in unnecessary tripping of a main breaker or, even worse, an explosion of equipment that was thought to be in good condition.

When system conditions change, the results that were obtained in the original fault-current coordination study may no longer apply to the current system. Unnecessary tripping, known as lack of selectivity, could be caused by poor coordination.

An equipment explosion could result from the interrupting capability of the circuit breaker being exceeded. Both indicate a clear need for an updated fault-current coordination study.

Utility systems delivering higher fault currents
The demand for electricity, particularly in the industrial and commercial environment, has been steadily increasing. Consequently, utility systems have grown much larger and have become capable of delivering much higher fault-currents at service points than in the past.

Therefore, protective devices that were properly applied at the time they were installed may have become inadequate after system changes, and the protective system may no longer be coordinated. When available fault current increases to the point at which it exceeds protective device interrupting and withstand ratings, violent failure is possible, regardless of how well the devices are maintained.

Protection in an electrical distribution system
System and equipment protective devices are a form of insurance. This insurance pays nothing as long as there is no fault or other emergency.

When a fault occurs, however, properly applied protective devices reduce the extent and duration of the interruption, thereby reducing the exposure to personal injury and property damage. If, however, the protective system does not match system needs, just as an insurance policy should keep up with inflation, it is no help at all. It is the responsibility of the system operator to ensure proper system protection and coordination.

Protective equipment set to sense and remove short circuits
In medium-voltage systems, the protective equipment for feeder conductors is often set to sense and remove short circuits, but not necessarily to provide overload protection of circuits. Device settings sometimes are purposely chosen low enough to sense and provide a degree of overload protection.

Operators should be aware of this so that a protective device that is set lower than necessary for coordination does not cause a false tripping action during system switching procedures. System protection coordination is an important consideration in switching systems with loop feeds and alternate sources.

To avoid false tripping action, operators should be aware of the settings and any probable temporary overloads or circulating currents during switching.

CIRCUIT PROTECTION CHECKLIST ESSENTIAL FOR ELECTRICAL SAFETY

THE IMPORTANCE OF HAVING A CIRCUIT PROTECTION CHECKLIST IN ELECTRICAL SAFETY

Before a system is designed or when unexpected events may occur, circuit designers should ask themselves the following questions:

What is the normal or average current expected?

What is the maximum continuous (three hours or more) current expected?

What inrush or temporary surge currents can be expected?

Are the overcurrent protective devices able to distinguish between expected inrush and surge currents and open under sustained overloads and fault conditions?

What kind of environmental extremes are possible? Dust, humidity, temperature extremes and other factors need to be considered.

What is the maximum available fault current the protective device may have to interrupt? Is the overcurrent protective device rated for the system voltage?

Will the overcurrent protective device provide the safest and most reliable protection for the specific equipment?

Under short-circuit conditions, will the overcurrent protective device minimize the possibility of a fire or explosion?

Does the overcurrent protective device meet all the applicable safety standards and installation requirements?

Answers to these questions and other criteria will help to determine the type of overcurrent protective device to use for optimum safety and reliability.

SELECTION OF LINEMAN ELECTRICAL PROTECTIVE EQUIPMENT BASIC INFORMATION AND TUTORIALS

How to select electrical protective equipment for lineman safety engineering?

The requirements for the hazard analysis and selection of protective clothing must first be defined.

Assess the workplace to determine if hazards are present, or are likely to be present, which require the use of personal protective equipment. If such hazards are determined, the employer should select and have each employee use, the type of personal productive equipment that will protect the affected employee from the hazards identified in the hazard assessment.

Train the employee to be knowledgeable with the following issues and scenarios:

• When personal productive equipment is necessary;
• What personal productive equipment is necessary;
• How to properly don, doff, adjust, and wear personal productive equipment;
• The limitations of the personal productive equipment;
and
• The proper care, maintenance, useful life, and disposal of personal productive equipment.

Include shock, arc, and blast assessments in the hazard analyses. Identify the selection, inspection, and use requirements for electrical personal productive equipment. Specify the type of clothing that is prohibited.

Utilize protective shields, protective barriers, or insulating materials to protect each employee from shock, burns, or other electrically related injuries while that employee is working near exposed energized parts which might be accidentally contacted or where dangerous electric heating or arcing might occur.

Protective clothing, including a complete multilayered flash suit with hood and face shield, may be required for the operation, insertion, or removal of a circuit breaker.

Calculate the incident energy (in cal/cm2) available at the work site in order to determine and the protective clothing required for the specific task. Additionally, determine a "Flash protection boundary" for all energized work.

At this boundary, exposed flesh must not receive a second-degree burn or worse. After determining the type, purchase the necessary protective
clothing and train employees on how to properly wear the gear.

POWER SYSTEM PROTECTION COORDINATION BASICS

When an electrical distribution system is designed and constructed, a fault-current coordination study should be conducted, and circuit protective devices should be sized and set according to the results of the study. In time, however, the electrical system configurations are often changed due to the changing needs of the end users.

If the coordination and capability of the electrical equipment are not reviewed at the time of the changes, faults could result in unnecessary tripping of a main breaker or, even worse, an explosion of equipment that was thought to be in good condition.

When system conditions change, the results that were obtained in the original fault-current coordination study may no longer apply to the current system. Unnecessary tripping, known as lack of selectivity, could be caused by poor coordination.

An equipment explosion could result from the interrupting capability of the circuit breaker being exceeded. Both indicate a clear need for an updated fault-current coordination study.

Utility systems delivering higher fault currents
The demand for electricity, particularly in the industrial and commercial environment, has been steadily increasing. Consequently, utility systems have grown much larger and have become capable of delivering much higher fault-currents at service points than in the past.

Therefore, protective devices that were properly applied at the time they were installed may have become inadequate after system changes, and the protective system may no longer be coordinated. When available fault current increases to the point at which it exceeds protective device interrupting and withstand ratings, violent failure is possible, regardless of how well the devices are maintained.

Protection in an electrical distribution system
System and equipment protective devices are a form of insurance. This insurance pays nothing as long as there is no fault or other emergency.

When a fault occurs, however, properly applied protective devices reduce the extent and duration of the interruption, thereby reducing the exposure to personal injury and property damage. If, however, the protective system does not match system needs, just as an insurance policy should keep up with inflation, it is no help at all.

It is the responsibility of the system operator to ensure proper system protection and coordination.

Protective equipment set to sense and remove short circuits
In medium-voltage systems, the protective equipment for feeder conductors is often set to sense and remove short circuits, but not necessarily to provide overload protection of circuits. Device settings sometimes are purposely chosen low enough to sense and provide a degree of overload protection.

Operators should be aware of this so that a protective device that is set lower than necessary for coordination does not cause a false tripping action during system switching procedures. System protection coordination is an important consideration in switching systems with loop feeds and alternate sources.

To avoid false tripping action, operators should be aware of the settings and any probable temporary overloads or circulating currents during switching.

TOP 10 HAZARDOUS TASKS IN ELECTRICAL WORKS

Typical hazardous tasks in electrical work

The following tasks are some examples of possible exposure to energized conductors:

a) Measuring, testing, and probing electrical system components;

b) Working near battery banks;

c) Opening electrical equipment enclosure doors or removing covers;

d) Inserting or pulling fuses;

e) Drilling, or otherwise penetrating, earth, walls, or ßoors;

f) Pulling conductors in raceways, cable trays, or enclosures;

g) Lifting leads or applying jumpers in control circuits;

h) Installing or removing temporary grounds;

i) Operating switches or circuit breakers;

j) Working inside electronic and communications equipment enclosures.

NEC FLAMMABLE CONDITIONS BASIC INFORMATION AND TUTORIALS

The National Electrical Code addresses hazardous conditions that create the potential for fires to occur. Environments that pose fire or combustion hazards are listed in Articles 500-510. Requirements covering specific types of facilities that pose additional hazards, such as bulk storage plants or motor fuel dispensing locations, are explained in Articles 511-516.

NEC Section (C)(2)(1) describes Class II, Division 2 locations classifications. These are listed as:

1. Locations where some combustible dust is normally in the air but where abnormal operations may increase the suspended dust to ignitable or explosive levels.

2. Locations where combustible dust accumulations are normally not concentrated enough to interfere with the operation of electrical equipment unless an “infrequent equipment malfunction” occurs that increases the level of dust suspended in the air.

3. Locations where combustible dust concentrations in or on electrical equipment may be sufficient to limit heat dissipation or that could be ignited by failure or abnormal operation of electrical equipment.

A variety of airborne environmental conditions that require classification are listed in Article 500. Class I covers locations specified in Sections [500.5(B)(1)] and [500.5 (B)(2)] where flammable gases or vapors are present, or could exist in the air in high enough quantities that they could produce explosive or ignitable mixtures. Section [500.5(B)(1) FPN 1] provides examples of locations usually included in Class I as the following:

1. Where volatile flammable liquids or liquefied flammable gases are transferred from one container to another.

2. Interiors of spray booths and areas in the vicinity of spraying and painting operations where volatile flammable solvents are used.

3. Locations containing open tanks or vats of volatile flammable liquids.

4. Drying rooms or compartments for the evaporation of flammable solvents.

5. Locations with fat and oil extraction equipment that uses volatile flammable solvents.

6. Portions of cleaning and dyeing plants where flammable liquids are used.

7. Gas generator rooms and other portions of gas manufacturing plants where flammable gas may escape.

8. Pump rooms for flammable gas or for volatile flammable liquids that are not adequately ventilated.

9. The interiors of refrigerators and freezers where flammable materials are stored in open or easily ruptured containers.

10. All other locations where ignitable concentrations of flammable vapors or gases are likely to occur in the course of normal operations.

SAFETY SWITCHES FOR ELECTRONIC EQUIPMENT BASIC INFORMATION

Fuses are typically installed in safety switches. Separately mounted fused safety switches are typically categorized as general-duty and heavy-duty types.

The general-duty type safety switch is rated at 240 V maximum and is typically used in residential and light commercial and industrial applications. The heavy-duty type safety switch is rated at 600 V maximum and is typically used in commercial and industrial applications.

Safety switches can typically be ordered with neutral assemblies and equipment grounding assemblies. There is currently no listing for safety switches that are to be used specifically with nonlinear loads.

It is recommended that the manufacturer be contacted to determine if oversized neutral assemblies can be installed in safety switches serving nonlinear electronic load equipment without voiding any listing requirements. In addition, the manufacturer should be contacted to determine if an isolated equipment grounding bus can be installed in the safety switch enclosure for those applications that require this grounding configuration.

Whenever fuses are utilized, there is a risk of a single-phasing condition if one fuse on a three phase system blows. Safety switches are generally not stored energy devices, and may not contain auxiliary functions such as undervoltage release or shunt trip attachments that help protect against a single-phasing condition.

This is an important consideration because some three phase electronic load equipment may be susceptible to damage if a single-phase condition persists. Other devices may need to be installed to provide proper single-phasing protection.

Blown fuse indicators
Recommended practice is to use blown fuse indicators for the quick and safe determination of the source of power outage affecting downstream electronic load equipment. Some safety switches and fused circuit breakers contain indicating devices located on the front enclosure that indicate a blown fuse condition. Some fuses contain an indicator light, providing visual indication that a fuse is blown.

Interrupting ratings
Interrupting ratings of new fuses or existing fuses should be evaluated to determine if proper interrupting ratings are applied. Interrupting ratings need to be reevaluated if there are any changes to the power system, such as installing K-factor transformers.

These transformers are typically specified or manufactured with a low impedance (%Z) resulting in a higher available short-circuit current on the secondary. This condition can be a problem especially where low interrupting capacity fuses, such as Class H fuses, are installed (Class H fuses have an interrupting rating of only 10 000 A).

BEST LOCATIONS FOR PANEL BOARDS AND SWITCH BOARDS OF ELECTRONIC EQUIPMENT BASIC TUTORIALS

Where should panel boards be located?

Switchboards and panelboards that support electronic load equipment and related loads should be properly designed and installed. Recommended practice is to use panelboards specifically listed for nonlinear loads if they serve electronic load equipment.

As a minimum, panelboards should be rated for power or lighting applications, and should not be a lighterduty type. Special attention should be given to the location and installation methods used when installing panelboards.

In addition, protective devices shall adequately protect system components, neutral buses should be sized to accommodate increased neutral currents due to harmonic currents from nonlinear electronic load equipment, and equipment ground buses should be sized to accommodate increased numbers of equipment grounding conductors due to the recommended practices of using insulated equipment grounding conductors and dedicated circuits for electronic load equipment.

Surge protective devices may also be installed external to, or internal to, the switchboards or panelboards.

Location
Panelboards that serve electronic load equipment should be placed as near to the electronic load equipment as practicable, and should be bonded to the same ground reference as the electronic load equipment.

Other panelboards located in the same area as the electronic load equipment that serve other loads such as lighting, heating, ventilation, air conditioning, and process cooling equipment should also be bonded to the same ground reference as the electronic load equipment.

Panelboards should be directly mounted to any building steel member in the immediate area of the installation. Isolation of a panelboard from the metallic building structure by an electrically insulating material, as an attempt to prevent flow of high frequency current through the panelboard, is not recommended practice.

The panelboard and metallic building structure, separated by a dielectric material, become capacitively coupled. The capacitive coupling presents a low impedance at high frequency defeating the original purpose.

NFPA 780-1997 requires effective grounding and bonding between objects such as structural building steel and a panelboard located within side-flash distance (approximately 1.8 m (6 ft), horizontally) of each other. Insulation materials, commonly used in an attempt to separate a panelboard from building steel, are rarely capable of withstanding lightningi nduced arcing conditions.

PROJECT RISK CONTROL - HIERARCHY OF RISK CONTROLS BASIC INFORMATION AND TUTORIALS

When assessing the adequacy of existing controls or introducing new controls, a hierarchy of risk controls should be considered. The Management of Health and Safety at Work Regulations 1999 Schedule 1 specifies the general principles of prevention which are set out in the European Council Directive.

These principles are:
1. avoiding risks
2. evaluating the risks which cannot be avoided
3. combating the risks at source
4. adapting the work to the individual, especially as regards the design of the workplace, the choice
of work equipment and the choice of working and production methods, with a view, in particular, to alleviating monotonous work and work at a predetermined work-rate and to reducing their effects on health
5. adapting to technical progress
6. replacing the dangerous by the non-dangerous or the less dangerous
7. developing a coherent overall prevention policy which covers technology, organization of work, working conditions, social relationships and the influence of factors relating to the working environment
8. giving collective protective measures priority over individual protective measures and
9. giving appropriate instruction to employees.

These principles are not exactly a hierarchy but must be considered alongside the usual hierarchy of risk control which is as follows:

S elimination
S substitution
S engineering controls (e.g. isolation, insulation and
ventilation)
S reduced or limited time exposure
S good housekeeping
S safe systems of work
S training and information
S personal protective equipment
S welfare
S monitoring and supervision
S reviews.

OVER CURRENT PROTECTIVE DEVICES FOR GENERATORS BASIC INFORMATION AND TUTORIALS

What are the basic overcurrent protection devices for generators?

As with other motors, NEC 445.11 requires a generator to have a nameplate giving the manufacturer’s name, the rated frequency, power factor, number of AC phases, the subtransient and transient impedances, the rating in kilowatts or kilovolt amperes, a rating for the normal volts and amps, rated revolutions per minute, insulation system class, any rated ambient temperature or temperature rise, and a time rating.

The size and type of OCPD will be based on this critical data. NEC 445.12 defines the basic overcurrent protection standards for various types of generators. A constant-voltage generator must be protected from overloads by either the generator’s inherent design or circuit breakers, fuses, or other forms of overcurrent protection that are considered suitable for the conditions of use.

This is true except for AC generator exciters.

Two-wire, DC generators are allowed to have overcurrent protection in only one conductor if the overcurrent device is triggered by the entire current that is generated other than the current in the shunt field. For this reason, the overcurrent device cannot open the shunt field.

If the two-wire generator operates at 65 V or less and is driven by an individual motor then the overcurrent device protection device needs to kick-in if the generator is delivering up to 150% of its full-load rated current.

When a two-wire DC generator is used in conjunction with balancer sets it accomplishes the neutral points for the three-wire system. This means it requires an overcurrent device that is sized to disconnect the three-wire system if an extreme unbalance occurs in the voltage or current.

For three-wire DC generators, regardless of whether they are compound or shunt wound, one overcurrent device must be installed in each armature lead, and must be connected so that it is activated by the entire current from the armature.

These overcurrent devices need to have either a double-pole, double-coil circuit breaker or a four-pole circuit breaker connected in both the main and equalizer leads, plus two more overcurrent devices, one in each armature lead.

The OCPD must be interlocked so that no single pole can be opened without simultaneously disconnecting both leads of the armature from the system.

The ampacity of the conductors that run from the generator terminals to the first distribution device that contains overcurrent protection cannot be less than 115% of the nameplate current rating for the generator per NEC 445.13.

All generators must be equipped with at least one disconnect that is lockable in the open position that will allow the generator and all of its associated protective devices and controls to be disconnected entirely from the circuits that are supplied by the generator.