User's Manual

ManualsBrandsFluke ManualsLaser Distance MetersFluke CV401 ClirVu

Concerned about arc-flash

and electric shock?

Want to comply with

NFPA 70E CSA Z462?

How can IR Windows help?

Infrared thermography has become a

well-established and proven method for

inspecting live electrical equipment. To

carry out tests, the thermographer usu-

ally works with live energized equipment

and requires a clear line of sight to the

target. Thermographers must therefore

be especially aware of the hazards, the

legislation and safety issues, and the

techniques and equipment best suited

to minimizing the risks when working in

these dangerous environments.

Introduction

Electrocution is the obvious danger faced by

anyone working on or near live electrical equip-

ment and it is clearly important to understand

shock hazards and wear appropriate protection.

However, most electrical accidents are not the

result of direct electric shocks. A particularly

hazardous type of shorting fault—an arc fault—

occurs when the insulation or air separation

between high voltage conductors is compro-

mised. Under these conditions, a plasma arc—an

“arc flash”—may form between the conductors,

unleashing a potentially explosive release of

thermal energy.

An arc flash can result in considerable

damage to equipment and serious injuries to

nearby personnel. A study carried out by the US

Department of Labor found that, during a 7-year

period, 2576 US workers died and over 32,000

suffered injuries from electrical shock and burn

injuries. 77 % of recorded electrical injuries

were due to arc flash incidents. According to

statistics compiled by CapSchell Inc (Chicago),

every day, in the US alone, there are 5-10 ten

arc flash incidents, some fatal.

NFPA 70E is the leading internationally recog-

nized safety standard for electrical safety in the

workplace. The Canadian Standards Association

has developed its own set of standards based

on NFPA 70E: CSA Z462.

These standards define a set of safe require-

ments for personnel working on electrical

equipment. To comply with the standards,

employers must carry out a hazard risk assess-

ment and ensure that all employees working in

a potential arc-flash hazard zone use appropri-

ate equipment and wear the right protective

clothing. Although it is not the responsibil-

ity of the thermographer to put in place the

appropriate safety procedures, it is important

to recognize and understand their need, and to

ensure that the correct procedures, equipment

and protective clothing are used.

White Paper

Safety technology

Summary of content (12 pages)

PAGE 1
Concerned about arc-flash and electric shock? White Paper Safety technology Introduction Want to comply with NFPA 70E CSA Z462? How can IR Windows help? Infrared thermography has become a well-established and proven method for inspecting live electrical equipment. To carry out tests, the thermographer usually works with live energized equipment and requires a clear line of sight to the target.
PAGE 2
The installation of IR windows, panes or ports allows a thermographer to inspect live electrical equipment without the removal of protective covers and the exposure of equipment. An arc-resistant window, unlike a port or pane, provides additional protection for the thermographer in the event of an arc flash resulting from unexpected component failures or work on other parts of the system.
PAGE 3
The current flow is therefore “comparatively” low but the explosive effects are much more destructive and potentially lethal. Unlike a bolted fault, it is difficult to predict exactly how much energy will be released by an arc fault. In particular, it is difficult to predict the duration of an arc fault as this depends on many factors, feedback mechanisms and the response of the over current protection devices.
PAGE 4
Inevitably, a serious arc flash will damage or even destroy the affected equipment. This leads to extensive downtime and expensive replacement and repair. An incident may also represent a failure on the part of the employer to comply with industry guidelines and regulations. This could result in a fine, litigation fees, increased insurance costs, expensive legal actions and accident investigations.
PAGE 5
8. Determine incident energy. Calculate the incident energy resulting from an arc fault at the working distance. 9. Determine flash protection boundary. Use the same calculations to estimate a ‘safe’ distance from the source of the arc hazard beyond which PPE is not required. This paper describes the Flash Protection Boundary in more detail later. Shock hazard analysis As the name implies, the determination of the shock hazard is an analysis designed to reduce the risk of electrocution.
PAGE 6
An important point here is that the flash protection boundary and the rules governing access within it take precedence over the shock hazard boundaries. So, for example, if the flash protection boundary is greater than the limited approach boundary then no unqualified person can be permitted in the limited approach area and even qualified workers must wear appropriate arc-resistant PPE here.
PAGE 7
What is appropriate PPE? Clearly, the potential injurious effects of an arc flash can be reduced by using a fire flame resistant (FR) suit of a suitable calorie rating to reduce the indecent energy on the body to an extent that the burns suffered are not life threatening. Most garments are tested and rated for incident radiation at a distance of either 18 inches or 24 inches. This roughly corresponds with the position of the head and chest when working directly on equipment.
PAGE 8
It is good working practice to make labeling clear and accurate; too much information is as bad as too little. If a system has several access points and arc flash hazards, label it with the parameters for the greatest hazard. online and on load coupled with the fact that IR Cameras cannot “see” through panel covers, thermographers face severe safety hazards when attempting to scan electrical distribution equipment. Taking measurements with a cover removed is not a safe option.
PAGE 9
How can infrared windows help? An infrared window provides a solid barrier between the thermographer and the live conductors. By careful design, it is possible to not only to reduce the trigger effects of an arc but also provide the thermographer with a far safer working environment. Thermography windows are relatively new technology, so there is no specific standard that relates to construction and testing.
PAGE 10
Crystal windows With a crystal infrared window, the R + A + T = 1 effects are multiplied with respect to the camera by a factor of two. These additional signals can be simplified and compensated for by making some practical assumptions based on real life applications. The first point to understand when investigating transmission is that the apparent error in the camera will not always be a negative, i.e. the camera may read LOW or it may read HIGH depending upon contributing factors.
PAGE 11
These confusing effects are increased further when mesh is used on both sides of a polymer optic. The radiation from the target is not transmitted in a repeatable manner through the IR window; instead, the radiation is in part deflected back into the panel and in part transmitted through the first mesh, only to be absorbed by polymer and the remaining energy deflected again by the outer mesh.
PAGE 12
Conclusions An electrical thermographer must work closely with live energized equipment and be aware of the dangers of this environment. In addition to the obvious hazard of electrocution, workers must be particularly aware of the dangers of arc flash and arc blast events. Up to 77 % of all electrical injuries are caused by arc flash incidents. It is important to remember that NFPA 70E does not protect personnel against the effects of arc blast.