

The SmartHat, designed by a Duke University engineer, would send an alarm to a construction worker who gets too close to heavy equipment. Photo Courtesy: Duke University
a Duke electrical and computer engineering researcher and SmartHat’s designer. “Most accidents and injuries occur because machine operators either don’t see workers or workers are faced away from the equipment.”
The SmartHat technology piggybacks on existing wireless networks at construction sites that monitor vehicle locations. Each piece of heavy machinery carries a wireless transmitter that broadcasts its location.
A silicon microprocessor, attached with Velcro to the crown of the SmartHat prototype, captures these free-floating radio-frequency waves with antennas. If the microprocessor determines the wearer is too close to equipment, it emits a high-pitched alarm that speeds up as man and machine move closer together.
“The beeping is an annoying sound that workers can hear through the noise of the work site,” Reynolds said. “If we mount the microprocessor in the hard hat, we create an echo chamber to amplify the warnings.”
However, the microprocessor’s ultimate location must be chosen carefully, said Jochen Teizer, a civil and environmental engineer at the Georgia Institute of Technology. OSHA requires that nothing compromise a hard hat’s ability to protect the wearer’s head during an accident.
“Including the SmartHat technology can’t create any danger to the wearer, such as creating a pinch point that could cause injury,” Teizer said. “For the technology to be feasible, you need to integrate it inside the hard hat. Integrating it into the plastic would be the final solution.”
Microprocessors should also have an extensive range, he said, to alert workers to fast-moving machinery.
By W. Jon Wallace, CSP, MBA
The National Fire Protection Association (NFPA) issued the revised 2009 edition of NFPA 70E®: Standard for Electrical Safety in the Workplace with an effective date of September 5, 2008. The 2009 edition of NFPA 70E® contains numerous revisions. Listed below is a summary of the major changes:
Contractor Relationships: Article 110.5 requires host employers inform contractors of known hazards covered by NFPA 70E® related to the contract employer’s work. The contract employer shall ensure that each of his/her employees is instructed in the hazards provided by the employer.
Training Requirements – Emergency Procedures: Article 110.6 requires employees exposed to shock hazards that are not reduced to a safe level by applicable electrical installation requirements be trained in approved methods of resuscitation, including cardiopulmonary resuscitation (CPR). The training shall be certified annually by the employer.
Electrical Safety Program Audit: Article 110.7 requires the written electrical safety program be audited on a frequency established by the employer.
Arc Flash Hazard Analysis: Article 130.3 requires the arc flash hazard analysis be updated whenever a major modification or renovation takes place. In addition, the analysis shall be reviewed periodically, not to exceed five years.
Arc Flash Protection Boundary: The criteria for the 4 feet arc flash protection boundary for voltage levels between 50 and 600 volts has been modified based on upstream protection device clearing time of maximum 2 cycles (0.033 seconds) and available bolted fault current of 50 kA or any combination not exceeding 100 kA cycles.
Equipment Labeling: Article 130.3 (C) states equipment shall be field marked with a label containing the available incident energy or required level of PPE.
Selection of Personal Protective Equipment: Article 130.7 contains several revisions with respect to arc flash PPE requirements. For example: Table 130.7 (C)(9) has been expanded to include additional job tasks such as performing infrared thermography as well as other non-contact inspections outside the restricted approach boundary. Additional categories of equipment, such as arc-resistant switchgear, have been added to the revised table. Table 130.7 (C)(10) has been revised and placed an a more user-friendly format.
Annex Revisions: The following annexes have been significantly revised – Annex F (Hazard/Risk Evaluation Procedure); Annex H (Simplified, Two-Category, Flame-Resistant [FR] Clothing System).
Please remember this article is intended as an overview and not a comprehensive summary of changes to the 2009 edition of NFPA 70E®.
آييننامه سيستم اتصال به زمين (ارتينگ)
فصل اول ـ تعاريف
اين فصل به تعريف اصطلاح ها و كلمههاي بكار رفته در آئيننامه ميپردازد.
1ـ زمين (ارت)1:
رسانندگي جرم زمين را در صورتي كه پتانسيل الكتريكي در هر نقطه از زمين به صورت قراردادي برابر صفر در نظر گرفته شود، زمين (ارت) مينامند.
2ـ سيستم اتصال به زمين (ارتينگ)2:
يك يا چند الكترود همراه با سيمهاي ارت را كه قابليت اتصال به ترمينال اصلي داشته باشند، سيستم اتصال به زمين (ارتينگ) مينامند.
3ـ الكترود ارت (زمين)3:
رسانا يا گروهي از رساناهاي متصل به هم است كه اتصال الكتريكي به زمين را فراهم ميكنند.
4ـ مقاومت الكترود ارت4:
مقاومت بين ترمينال اصلي زمين و كره زمين است.
5 ـ امپدانس حلقه اتصال به زمين5 :
امپدانس حلقه جريان اتصالي زمين است كه شروع و پايان آن نقطه اتصالي است و با ZS نشان داده ميشود.
ـ حلقه اتصالي زمين در سيستمهاي مختلف به شرح ذيل است:
الف ـ سيستمهاي TN
نقطه شروع (محل اتصالي)، از بدنه دستگاه به ترتيب به سيم ارت، شينه ارت، شينه نول، نقطه ترانس، سيمپيچ ترانس، سيم فاز اتصالي و نقطه اتصال به بدنه.
ب ـ سيستمهاي TT و IT
نقطه شروع (محل اتصالي)، سيم اتصال به زمين، الكترود زمين، زمين، الكترود سيستم، شينه نول، نقطه صفر ترانس، سيم فاز اتصالي و نقطه اتصالي.
6 ـ اتصالي:
حالتي از مدار است كه جريان در مسيري غيرعادي يا بدون اينكه پيشبيني شده باشد يا در نظر گرفته شود، جاري ميشود. اين جريان امكان دارد از نقص در عايقبندي يا از بستهاي به كار رفته بر روي عايق رساناها ناشي شود.
7 ـ جريان اتصال به زمين (جريان اتصال كوتاه)6 :
اضافه جرياني است كه در نتيجه بروز اتصالي با امپدانسي قابل چشمپوشي بين هاديهاي با پتانسيلهاي مختلف در شرايط عادي كار برقرار شود.
8 ـ جريان نشتي زمين7 :
جريان جاري به زمين يا رساناهاي ديگري را كه مدار الكتريكي آنها به زمين راه دارد، جريان نشتي زمين مينامند. در صورت استفاده از خازن در مدارها، امكان دارد جريان مذكور داراي مقدار جزء خازني هم باشد.
9ـ سيم اتصال به زمين (سيم ارت)8 :
سيم حفاظتي را گويند كه ترمينال اصلي ارت تأسيسات را به الكترود ارت يا ساير قسمتهاي اتصال به زمين وصل ميكند.
بقيه آيين نامه را در لينك ذيل ملاحظه فرماييد :
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