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Фотовспышка All Things: факты, стандарты и защитные перчатки

Время: 2020-03-09 Хиты : 1

Фотовспышка All Things: факты, стандарты и защитные перчатки

Arc flash it sounds serious, and with over 30,000 incidents and 400 fatalities per year*, it"s deadly serious. An arc flash occurs when there is a sudden release of electrical energy through the air caused by a fault in an electrical circuit. This leads to a rapid rise in temperature and pressure between electrical conductors, usually causing an explosion known as an arc blast.

A typical arc flash incident can be inconsequential, but those that produce severe arc blasts can be extremely dangerous and damaging to surrounding life and property. Such explosions typically occur without any warning - leading to electrical equipment being destroyed entirely, along with severe injury (or even death) to anyone within several feet of the blast.

Wearing the proper PPE and knowing what you"re up against is a must-have when on the job, especially when you"re working around environments that have the potential for arc flash and blasts. To help you out, we"ve put together a concise explanation of everything you need to know about arc flash.

Just How Much Power is in an Arc Flash?

Вот"s a quick look. The massive energy released in an arc flash fault gives off bright, intense light and thermal radiation with temperatures that can reach or exceed 35,000° Fahrenheit (F) or 19,400° Celsius (C) at the arc terminals. To fully understand that kind of power, look at the following comparisons:

Hot summer day: 100° F (38° C)

Surface of the Sun: 10,000° F (5,540° C)

Arc at arc terminals: 35,540° F (19,700° C)

High-voltage arcs can result in an arc blast that instantly heats metal conductors and surrounding objects to vaporizing temperatures, blasting super-heated shrapnel, pressure waves, and expanding plasma outward with extraordinary force.

Sound intense? It is.

The radiant effects of this can be seen on the often ablated and eroded adjacent walls and equipment as well as on personnel in its path. Blasts can knock workers off their feet, resulting in broken bones or lead to electrocution, as well as cause severe burns, ruptured eardrums, collapsed lungs, and even death.

Though both occur from the same arc fault, it is important to note that an arc flash is different from an arc blast.

What OSHA Says about Arc Flash

In the United States, the Occupational Safety and Health Administration (OSHA) requires employers to protect employees from electrical hazards, including arc flash, by requiring workers to have head-to-toe protection, including safety helmets, face shields, flame-resistant protection, and hand and ear protection.

To help meet the performance requirements of the OSHA standards for electrical safety, employers also look to NFPA 70E, which is a comprehensive standard that contains detailed information on how to protect workers from arc flashes. Though not an OSHA requirement, NFPA 70E outlines how to comply with OSHA"s electrical safety requirements. This symbiotic relationship between NFPA 70E and OSHA electrical safety standards helps to increase safety in the workplace.

Types of Arc Flash-Rated Gloves

Gloves are a crucial piece of PPE for electrical workers and need to consist of high dielectric and physical strength with flexibility and durability to mitigate the impact of an arc flash. There are two main categories of gloves that protect against arc flash:

Rubber insulating: Made of rubber, these gloves are the traditional way to work around arc flash hazards and can be bulky. According to NFPA 70E and CSA Z472 standards, all types of work with shock exposures of greater than 50 volts (V) require the use of rubber insulating gloves.

Non-rubber gloves: Made of either leather or coated material, these gloves are inherently flame-resistant (FR) (like aramid, leather, wool, glass, and coated nylon) or treated (as with Pyrovatix, Proban, or Indura). These gloves combine the required dielectric properties of an electrical protective glove with flexibility, strength, and durability.

To choose the best glove for a job, you need to understand the different arc flash ratings. These ratings are based on Hazard Risk Category (HRC) standards and the Arc Thermal Protective Value (ATPV). HRC is the safety standard that shows the minimum amount of PPE protection a worker needs based upon the potential exposure to a hazard, ranging from 0 to 4, with 4 being the highest risk. ATPV is the incident energy needed to cause a second-degree burn; this value is provided in calories per centimeter squared (cal/cm²).

ASTM F1506 is the standard that determines the HRC of a glove, and ASTM F2675 is the standard that determines ATPV. NFPA 70E mentions the ASTM F2675 for arc flash testing of gloves and OSHA 1910.269 requires arc-rated gloves for exposures greater than 14 cal/cm².