Abstract of Special Research Report (RR-2002)
National Institute of Occupational Safety and Health, Japan
Time-Frequency Analysis of Ultrasonic Echoes and its Application to Nondestructive Evaluation of Thermal Damage of Steel
RR-2002-1 |
Shiwei MA, Tetsuya SASAKI, Etsuji YOSHIHISA and Takashi HONDA |
: Recent trend to extend the original design life of pressure vessels and piping may increase the possibility of failure accident of these components caused by material degradation due to creep or creep-fatigue. Since sudden rupture of these components usually results in a serious industrial accident, such material damages must be detected using nondestructive evaluation technique to ensure the safety of workers at the industrial sites. Although there are a lot of different methods in nondestructive evaluation technique, ultrasonic pulse-echo technique is supposed to be one of the best methods to detect creep or creep-fatigue damage. In this method, reflected ultrasonic echoes by material internal defects and specimen interface often exhibit critical time and frequency information. However, it is difficult to determine creep or fatigue-creep damage using conventional signal processing technique. To conquer such a difficulty, the time-frequency analysis method is applied in this study. Because the time-frequency analysis method can provide an effective tool to represent a signal in a two-dimensional time and frequency plane, it is possible to obtain frequency dependent ultrasonic characteristics related to certain material properties in a time-frequency plane rather than only in a time domain or frequency, and these characteristics can be applied to identify internal defects or to assess creep damage of crucial structure material. |
Requirements of Prevention Equipment against Falling from Roof
RR-2002-2 |
Yasumichi HINO |
: Falling Accidents at the construction site of low rise houses have been recognized as the major cause of fatal accidents since the occupational safety and health law was instituted in 1972. There is a decreasing trend of the accidents in the last two or three years. It is thought that the reasons are due to "popular use of precedent scaffold installation method" and "decrease in the number of construction works". |
Fundamental Study on Wind Pressure Acting on Temporary Scaffolds
RR-2002-3 |
Yasumichi HINO, Katsutoshi OHDO, Songpol PHONGKUMSING, Eizo MARUTA and Makoto KANDA |
: The number of construction accidents has gradually decreased since the Occupational Safety and Health Law was instituted in 1972, and the number of fatal accidents has decreased 30 percent since 1972. However, approximately seven hundred fatal accidents still happen every year. And also, 10 percent of collapse accidents in serious accidents in which 3 or more workers were killed or injured are caused by wind. Especially, not only construction workers but also pedestrians were killed or injured by the collapses of temporary scaffolds due to wind. Therefore, the prevention methods for collapses of temporary scaffolds due to wind should be established. |
Stability of Counter forted-type Sheet Pile Retaining Wall --For Sandy Ground--
RR-2002-4 |
Yasuo TOYOSAWA, Noriyuki HORII, Satoshi TAMATE, Makoto ETOH, Mitsuo SATO, Mitsuru EGUCHI and Norio FUJITA |
: About 100 workers die in accidents during excavation at construction sites every year in Japan. There are many construction processes involved in the assembly of retaining walls such as installing wales, struts, braces etc, as well as dismantling such materials, and the complexity of these processes is one of the main causes of such accidents. |
Survey on Commuting Stress and Accidental Falls of Elderly Workers on the Way to and from Work --Building-Maintenance Industry--
RR-2002-5 |
Hisao NAGATA and Sunyoung LEE |
: In the building-maintenance industry where many elderly workers are employed, the ratio of accidents on the way to and from work is higher than other sectors, and accidents due to falling on the way to and from work often occur. Accordingly, we conducted a survey on workers in the building-maintenance industry who are 60 years old and over. In the building-maintenance industry, the labour force in particularly is ageing, and falling accidents on the way to and from work makes up a sizable proportion of the overall figure. |
The Dependence of Initial Pressure for the Autoignition Temperature of Flammable Liquid
RR-2002-6 |
Haruhiko ITAGAKI |
: Autoignition temperatures (AIT) of flammable liquids have been measured by many researchers. Especially, many data by the ASTM method have been reported. However, a fire sometimes happened at the chemical plant due to the autoignition of some flammable liquids though those were dealt with under the lower temperature than the data measured by the ASTM method. |
Study of Terms Connection in the Database for Explosion and Fire Accidents
RR-2002-7 |
Teruhito OTSUKA and Haruhiko ITAGAKI |
: According to the development of Internet, various search methods have been invented recently. Because of large number of web pages, page ranking system has been succeeded on Internet. But such method is not applicable for the database for explosion and fire accidents, because of lack of linkage system and paucity of same accident. |
Characteristics of a New Apparatus for Measuring Ignition Energy of Dust Clouds having a Dispersion Mechanism by Ultrasonic Vibration
RR-2002-8 |
Mizuki YAMAGUMA, Kwang-SEOK CHOI and Tsutomu KODAMA |
: This paper describes a novel apparatus for measuring the minimum electric spark ignition energies of combustible dust clouds. Instead of a transient suspended dust cloud by a blast of compressed air as in the conventional Hartmann tube apparatus, this one forms a curtain-like, constant downstream of dust in an explosion chamber by combining an ultrasonic vibrator, a sieve, and a specially designed dust hopper. While passing through the gap of two electrodes placed in the middle of an explosion chamber, sparks are given to the dust stream to determine its minimum ignition energy (MIE). The concentration of a dust cloud is widely controllable through the current to the vibrator. The apparatus is equipped with two pieces of coarse metal mesh functioning as flame arresters and are placed just below the sieve and over the base of the explosion chamber to protect the chamber and to enable the recycling of unburned dust. By comparing the MIE values of several samples of dust with those obtained by the conventional method, the new method was confirmed to give reliable data. |
Electromagnetic Disturbance of Large-Scale Crane due to Medium Broadcasting and Countermeasures
RR-2002-9 |
Hajime TOMITA |
: IWhen a large-scale crane, such as a tower crane or a rough-terrain crane, is used under the influence of a high electromagnetic field caused by a broadcast wave at medium frequency, the voltage induced in the hook can reach 1kV and causes the electric shock to workers. The current induced in the crane can cause the overload-preventive device to malfunction. However, the intensity of induced current in a large-scale crane is not well understood. |
Questionnaire Survey regarding Manual AC Arc Welding Operation
RR-2002-10 |
Tatsuo MOTOYAMA, Hajime TOMITA and Eiki YAMANO |
: Arc welding is a high-risk operation because it is very difficult to remove exposed live parts, such as the welding rod and the welding rod holder, from a manual AC arc-welding machine. The Voltage-Reducing Device for an AC arc-welding machine (VRD) is designed to prevent electric shock caused by the arc-welding operation. |
Study on Usage of Safety Belt and Scope of Airbag for Fall Protection
RR-2002-11 |
Kiyoshi FUKAYA |
: Two fall protection measures were studied. One is a fall arrest system by a safety belt, and another is an airbag system for fall protection which absorbs shock to a worker. |