Going the extra mile for safety
Consolidated Edison, in conjunction with the Utility Workers Union of America (Local 1-2), recently concluded more than three years of rigorous testing of flame-resistant (FR) protective apparel at the independent test laboratories of KEMA, located in Chalfont, Pa. With a shared goal of providing maximum protection for employees, the two organizations intended to identify clothing that was safer and more comfortable than what Con Ed was using.
"Safety is our foremost concern," says Local 1-2 President Manny Hellen.
Unprecedented testingSeveral characteristics of the test series are noteworthy and unprecedented:
- It is the largest and most comprehensive FR clothing arc testing ever conducted by an end-user;
- Arc blasts were generated on real-world equipment and at common system energies; and
- Major emphasis was placed on underground, or "arc-in-a-box," testing.
This work assumes even greater importance in light of the NFPA 70E Standard, which requires all employees working around energized electrical equipment, not just utility personnel, to wear flame-resistant protective apparel. The KEMA test results identified flame-resistant protective apparel1 (1 Indura(R) and Indura(R) Ultra Soft(R) protective clothing was identified as providing superior safety and protection against arc and fire) that provides superior safety and protection against arc and fire, along with a higher level of comfort, than the clothing previously issued to employees.
"There's a common but dangerous misperception that heavy cotton won't burn," says Local 1-2 Shop Steward Ed Smith. "In fact, it ignited easily, burned vigorously and consumed the clothing quickly. If you work around electricity, you need to be in FR clothing."
Real-world conditionsCon Ed and UWUA recognized that existing test facilities and data were not completely adequate for this testing, because standard testing is conducted in open air while a major portion of Con Ed operations are underground. When generated in an enclosed space (referred to as "arc-in-a-box"), electric arcs act differently than uncontained blasts.
The two organizations, thus, went to the KEMA lab, which was able to simulate real-world test conditions on various types of equipment. A cement enclosure was constructed to the same interior dimensions as a typical manhole, and equipment used in daily operations was installed inside. Cables, joints and other gear were real-world items, and the work was executed by Con Ed employees following standard work practices.
The splicing was done inside the simulated manhole, with the splices intentionally shorted to create an arc flash. The short was created by drilling a hole in the splice and inserting a copper nail with binding wire. The wire was run to a ground, then hooked to a high-tension lead from a KEMA generator. The cables were then faulted in the enclosure using test circuit parameters equal to actual field conditions.
Wired-up mannequinsInstrumented test mannequins were placed in the manhole to simulate work crews. The mannequins were dressed in appropriately sized garments of various fabrics from several manufacturers to evaluate their resistance to heat and pressure waves.
The mannequins were instrumented with sensors called thermocouples, which measure temperature rise, and thus can be used to predict the location and severity of any resultant body burn injury. Thermocouples were also placed outside the mannequin's clothing to measure the incident energy of the arc, which allowed for a direct quantification of the energy blocked by the clothing.
All processes leading up to the arc, and control of the arc itself, were conducted and supervised by KEMA Power Test personnel. The lead to the shorted splice was then energized at 25,000 amps at 7.6kv, and a large explosion resulted. Multiple camera ports allowed for direct, real-time monitoring of the clothing, and an infrared camera captured arc intensity and direction, as well as any post-exposure fire.
Multiple testsTesting was eventually expanded to include overhead work, utilizing instrumented mannequins in a bucket truck. Overhead testing was conducted at 10,000 amps at 7.6kv. Testing repeatedly demonstrated that the clothing which fared well in underground testing also performed well in overhead operations.
Hundreds of exposures were conducted over several years to fully characterize the performance differences among FR fabrics and garment styles.