NIST Tech Beat - August 30, 2007

The National Institute of Standards and Technology (NIST) conducted experiments this week in Sharon Hill, Pa., on the hazards of fires under residential floors, which can surprise firefighters by hastening structural collapse, and on technologies, such as thermal imagers and acoustic devices, that firefighters might use to assess the danger of collapse.

The test burns, carried out in cooperation with the Delaware County (Pa.) Emergency Services Training Center (ESTC), are part of a multi-year NIST project to investigate potential tools and techniques for predicting structural collapse. NIST previously conducted a series of structural collapse fire tests with the support of the U.S. Fire Administration (USFA), part of the Department of Homeland Security (DHS).

Approximately 20 percent of the deaths of fire fighters in structure fires over the past 10 years have been as a result of structural collapse. Predicting a potential collapse is one of the most challenging tasks facing an incident commander at a fire scene. Usually, the lack of information on the building construction, fire size, fire location, fire burn time, building condition, fuel load and other factors makes the task nearly impossible.

To gain a better understanding of the factors, NIST fire engineers built and burned multiple 16 x 16 foot, wood frame, two-story structures at ESTC. The test scenario simulated a situation in which a fire begins in the basement level, posing a risk to firefighters entering on the first floor. The experiment explored the effects of thermal exposure and weight loading on various building construction types and materials. An array of instruments recorded time and temperature data until the structure collapsed. Sensors also provided comparative data on the effect of different common floor coverings and structural design on the progress of the fire.

NIST fire engineers used three different types of thermal imaging (using barium-strontium-titanate, vanadium oxide and amorphous silicon detectors) to track the spread of the heat through the flooring materials. The researchers also collected data from a prototype acoustical device that is designed to detect structural movement in advance of a collapse. Subsequent analysis should reveal the technology’s capabilities to warn of impending structural collapse.

In addition to NIST, the National Fallen Firefighters Foundation (NFFF) and State Farm® are documenting the experiment, and will incorporate the results in a firefighter safety DVD to be released next year. NIST will publish its findings from the Delaware County fire experiments next year.

Factories have much to gain from wireless technology, such as robot control, RFID tag monitoring, and local-area network (LAN) communications. Wireless systems can cost less and offer more flexibility than cabled systems. But factories, such as auto production plants, are challenging environments for wireless systems, as verified by tests conducted recently by the National Institute of Standards and Technology (NIST). Heavy industrial plants can be highly reflective environments, scattering radio waves erratically, and interfering with or blocking wireless transmissions. Electromagnetic interference may hinder the auto industry and other manufacturing sectors in trying to take full advantage of wireless networking.

The NIST tests aim to quantify what has been, until now, a nebulous problem. In a partnership with the U.S. Council for Automotive Research (USCAR), NIST plans to develop a statistical representation of the radio propagation environment of a production floor as a basis for developing standards to pre-qualify wireless devices for factories. NIST researchers conducted the initial tests at an auto assembly plant in August 2006, and completed additional tests this month at an engine plant and a metal stamping plant.

The manufacturing plants that NIST tested were crowded with stationary and mobile metal structures, such as fabrication and testing machinery, platforms, fences, beams, conveyors, mobile forklifts, maintenance vehicles and automobiles in various stages of production. NIST monitored frequencies below 6 gigahertz (GHz) for 24-hour periods to understand the background ambient radio environment. This spectrum survey showed that interference from heavy equipment (“machine noise”) can impair signals for low-frequency applications such as those used to in some controllers on the production floor. A detailed analysis of a common wireless LAN frequency band (channels from 2.4 to 2.5 GHz) found heavy, constant traffic by data transmitting nodes, wireless scanners and industrial equipment. And signal-scattering tests showed the potential for high levels of “multipath” interference, where radio signals travel in multiple complicated paths from transmitter to receiver, arriving at slightly different times.

NIST researchers will use these data in studies aimed at pre-qualifying wireless devices for use in industrial environments. In the meantime, NIST researchers have identified a number of steps that can be taken to minimize radio interference on the factory floor, including use of licensed frequency bands where possible, and restrictions on use of personal electronics in high-traffic frequency bands such as 2.4 GHz. Other suggestions include installing absorbing material in key locations, use of wireless systems with high immunity to electromagnetic interference, use of equipment that emits little machine noise, and use of directional antennas to help mitigate multipath interference when transmitter and receiver are close together.

If you want to exploit the ability of single-walled carbon nanotubes (SWCNTs) to absorb, fluoresce and scatter light, take the advice of a sandlot quarterback and “go long.”

In the Aug. 29, 2007, issue of the Journal of the American Chemical Society,* researchers at the National Institute of Standards and Technology (NIST) show that length has a significant impact on enhancing the optical properties (absorption, near-infrared fluorescence and resonant Raman scattering) of these tiny cylinders made up of single-sheet rolls of carbon atoms. Normally, material properties like refractive index are constants, but, say the NIST researchers, at the nanoscale sometimes size matters in unusual ways. The ability to manipulate these optical properties may one day lead to the development of SWCNTs as microscopic optical sensors, biological probes and highly-specific drug-delivery systems.

To make the optical measurements possible, the researchers used size-exclusion chromatography to separate DNA-wrapped nanotubes based on their length (the DNA enables the SWCNTs to dissolve in water and facilitates their separation by chromatography). Borrowing tools from biology, the scientists consolidated many separation runs to generate different fractions—ranging in size from less than 50 nanometers to greater than 500 nanometers—in concentrations higher than previously reported for length-sorted SWCNTs. This allows SWCNTs of various lengths to be studied individually with higher accuracy and by more techniques.

The optical response of SWCNTs proved to be dependent on nanotube length for all three characteristics examined. The strength of the absorption changes in direct proportion to length for nanotubes approaching a micrometer in length. This relationship, in turn, affects other important optical properties of the nanotubes including near-infrared fluorescence and resonant Raman scattering. The researchers suggest that the length dependence may be a consequence of quantum mechanical phenomena, raising the possibility that at these length scales the usual notion of a constant material property may need to be rethought.

Although the longest nanotubes studied in the NIST experiment had the most intense optical responses, the researchers suggest that length dependence is not without bounds. Defects, kinks, impurities and tube deformations are all potential limiting factors.

* J.A. Fagan, J.R. Simpson, B.J. Bauer, S.H. De Paoli Lacerda, M.L. Becker, J. Chun, K.B. Migler, A.R. Hight Walker and E.K. Hobbie. Length-dependent optical effects in single-wall carbon nanotubes. Journal of the American Chemical Society 29 (34), pp. 10607 -10612, 2007.

The National Institute of Standards and Technology (NIST) recently released an improved version of its Personal Identity Verification (PIV) Data Generator, a downloadable Java application (http://csrc.nist.gov/piv-program/downloadable-piv-software.html) that can be used to create test data for evaluating PIV systems and cards.

The credit card-sized PIV card contains integrated circuit chips for storing electronic information, a personal identification number and protected biometric data—a printed photograph and two electronically stored fingerprints. Use of these cards by federal employees and contractors is mandated by October 2008 under the Homeland Security Presidential Directive 12 with the technical and operational requirements specified by Federal Information Processing Standard (FIPS) 201. FIPS 201 was developed by NIST in conjunction with other organizations and approved by Commerce Secretary Carlos Gutierrez in February 2005.

The latest version of the PIV Data Generator has been enhanced for dynamic data production and is designed for use with the PIV Data Model Tester (available from the same Web page). The test data objects produced by the PIV Data Generator conform to the FIPS 201 requirements as well as the guidelines set forth in three NIST publications, Interfaces for Personal Identity Verification (SP 800-73-1), Biometric Data Specification for Personal Identity Verification (SP 800-76-1) and Cryptographic Algorithms and Key Sizes for Personal Identity Verification (SP 800-78-1). FIPS 201, as well as the three special publications, may be obtained at http://csrc.nist.gov.

A separate utility within the same download as the Data Generator—the PIV Data Loader—can be used to place generated data onto blank PIV cards to create customized cards for testing the conformance to FIPS 201 and the interoperability of PIV security system components.

Konrad Lehnert, a physicist at JILA, is a finalist for the 2007 Service to America medals, presented annually by the non-profit, non-partisan Partnership for Public Service to celebrate excellence in the federal civil service. JILA is a joint institute of the National Institute of Standards and Technology (NIST) and the University of Colorado at Boulder.

Lehnert is among five finalists in the Call to Service category, which recognizes professional achievements that “reflect the important contributions that a new generation brings to public service.” Lehnert, who is just 36, has conducted groundbreaking research to use quantum mechanics to improve measurement science. Read about one of his research projects at “New JILA Apparatus Measures Fast Nanoscale Motions.”

Medal recipients, selected in a thorough vetting process that includes interviews of the finalists, will be announced next month and honored at an awards ceremony in Washington, D.C. Three other NIST physicists have previously won medals in the Service to America program, which began in 2002. Read more at www.servicetoamericamedals.org/SAM/finalists07/c2sm/.

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Editor: Michael Baum

Date created: August 30, 2007
Date updated: August 30, 2007
Contact: inquiries@nist.gov