Abstract of Special Research Report (RR-18)

National Institute of Occupational Safety and Health, Japan

Studies of Explosive Characeristics of Hydrogen (1st Report) --Effect of High Pressure on the Flammability Limits of Hydrogen--

RR-18-1

Shozo YAGYU, Hidenori MATSUI, Toei MATSUDA and Hiroshi YASUMOTO

: In industries, hydrogen is often used at high pressures and a knowledge of flammability limits of hydrogen under high pressures is required for safe operations. The authors measured flammability limits of H₂ - Air, H₂ - O₂ and H₂ - O₂ - N₂ mixtures at pressures from atmospheric to 80 kg/cm² and examined the effect of high pressures on flammability limits of the mixtures.
    The mixtures were ignited in a stainless steel cylinder (7.5 cm in diameter and 50 cm in height) by passing a current through a Pt wire located at the bottom of the cylinder.
    Lower and upper limits of flammability for H₂ - Air and H2-O2 mixtures vary specifically with pressures. The lower limits for those mixtures increase from 4 to 5 % H₂ corresponding with pressure increase from atmospheric to about 30 kg/cm^2. They, however, decrease very slowly with the higher pressures, resulting in a little higher even at 80 kg/cm² than those at atmosphere. On the other hand, the upper limits for H₂ - Air mixtures decrease from 75 to 71% corresponding with pressure increase from atmospheric to about 10 kg/cm² and increase at the higher pressure, getting to 76% at 80 kg/cm^2. Similarly, the upper limits for H₂ - O₂ mixtures decrease from 95 to 94 % and again reach 95 % at 80 kg/cm^2. The lower and upper limits at 80 kg/cm² are nearly the same at atmospheric pressure.
    Flammability limits for the system H₂ - Air - N₂ at pressures of 20 kg/cm² and 50 kg/cm², presented on a triangular diagram, are narrower than those at atmosphere. Accordingly, the flammability limits for the system H₂ - O₂ - N₂ are estimated not to enlarge more with the pressure elevated to about 80 kg/cm² than those at atmosphere.

The Tensions in Wire-ropes of Ships' Derricks --on Union Purchase--

RR-18-2

Teizo HAKAMAZUKA and Soichi KUMEKAWA

: We measured the tensions of wire-ropes on union purchase in which a pair of derricks is used in combination on ship rigs.
    The measurements were followed by 7 typical layouts of derricks (Table 1), and the results are as the following.
  1) The tensions of wire-ropes when the cargo load runs from side to side horizontally. The datum are Table 2 - 19. About 5 times tension of cargo load was acting at maximum in the topping-lift wires of this derrick, and about 3 times in guys.
  2) The tensions of wire-ropes at lifting up the load. Table 20 is the result. The maximum dynamic loads in topping-lift-wires were approximately 1. 5 to 3 times of cargo load.
  3) The shock loads in wire-ropes at sudden stop when cargo is moving down (Table 21). The maximum ratios of shock load to static load were about 6 in cargo runners, about 2. 5 in topping-lift wires or center guy and about 4 in guys.
  4) The tensions in wire-ropes when cargo load is swinging in perpendicular or parallel direction to the ship center-line (Table 22). In this case, the max. load in wire-ropes was added approximately to the static load.
    Besides, for the purpose to find the most suitable fixed position of the guy, we calculated the tensions of guys when a unit horizontal force is acting on the boomhead. The datum are Fig.7-14. On these cases shown at b < 4 m on θ = 25°, b < 3.3 m on θ = 35°, b < 3 m on θ = 40° and b < 2.8 m on θ = 45°, the positions where the guy tension get the minimum value are in the forward side to goose-neck. And on another cases the positions of the goose-neck side are desirable.

The Effect of Vessel Size on Gas Phase Explosion Pressures in Closed Vessels --A Contribution for the Testing Methods of Flameproof Electrical Equipments--

RR-18-3

Heizaburo TURUMI and Toshihiro HAYASHI

: The effect of vessel size on explosion pressures has been investigated in closed cylindrical and spherical vessels. The vessels were relatively small and their capacities ranged from 30 cm³ to 2 litres. L/D, the ratio of vessel length to inner diameter for cylindrical vessels, were all 1.77.
    The flammable mixture used was that of hydrogen and air (30 and 50 vol.% hydrogen in air), because it had been intended to apply the results of investigation for the practical testing of Flameproof Electrical Equipments. Therefore, the initial pressures of the gas mixture were confined below 2 kg/cm² (gauge).
    The authors, first of all, derived from rather simple theoretical considerations that the explosion pressures had to be approximately proportional to the initial pressures for a certain vessel. The equation may be written as follows ;
           P _e = A ( P _i + 1 )
where : P _e = explosion pressure (a difference from a initial pressure P _i ).
        A = constant, which is equal to the explosion pressure when P _i = 0 (atmospheric) for a given vessel.
    And if the constant A is shown as a function of vessel size ( V ), the explosion pressure may be calculated for a given size ( V ) and initial pressure ( P _i ) from the following relation, other factors affecting the explosion pressure being constant or negligible.
        P _e = { g( V )} ( P _i + 1 )
    Experiments were carried out to ascertain whether practical explosion pressures measured showed good agreement with the above equation or not.
    The results showed that the agreement was fairly good, and the experimental explosion pressures were shown by the following equations ;
        P _e = (4.75 + 0.55 log V )( P _i + 1 ) for 30 vol. % mixtures, or
        P _e = ( 2.9 + 0.7 log V )( P _i + 1 ) for 50 vol. % mixtures.
    The results may be applied not only for the testing of Flameproof Electrical Equipments, but also to other fields concerning to gas phase explosions in relatively small size of vessels.

Study of the Human Operator-Plate Mill System --Development of the Hardware and Software--

RR-18-4

Masashi OKAWA, Takehiko NISHIMOTO, Masataka OSHIDA and Setsuo KAWAHARA

: The aim of this research is to develop a hardware and a software requiring- the evaluation, from the point of view of the man-machine system engineering, about the human operator-plate mill system (as man-machine system) performance.
    The concrete goals are indicated as follows.
  1) constructing the mathematical model of the human operator-plate mill system (HOPMS) characteristics,
  2) analyzing HOPMS operations,
  3) procedure for HOPMS training,
  4) evaluating HOPMS effectiveness
    The system analysis conducted in the preparation stage were as follows.
  1) drawing up the system flow chart (including the standard operational sequence analysis)
  2) analyzing the system criticality,
  3) analyzing the man-machine interface,
  4) analyzing the man-machine dynamics,
  5) setting the system training requirements,
    The hardware is consisted of the computing part (using MELCOM EA-7160, the simulation of the main motor dynamics, the elongation curve, the temperature of a steel plate and the total system control are performed.) and the mill control desk (functionally similar to the real desk) the relay box, the evaluation display panel (using A/D converter, evaluation data are displayed and/or printed out), the recording part (the physical volumes such as voltage, speed and etc., the operational volumes and evaluation functions are recorded) and the AVR. The software for the system evaluation was considered in terms of the operational efficiency and quality and misoperation.
    The tentative evaluation functions were derived.

Elimination of Static Electricity by Use of Electrically Conductive Fiber

RR-18-5

Yasuyuki TABATA

: With the widespread acceptance of synthetic fiber, which absorbs relatively little moisture even at high humidity, the problems and dangers of static electricity have been greatly increased. Especially, the discharge of static electricity can take the form of a spark, quite often an energetic spark.
    If the spark discharge should occur in an explosive atmosphere, disastrous consequences could follow.
    Safe methods for eliminating static electricity have been investigated in various fields ; utilization of the corona discharge is one of them.
    It has been recognized that the fine metallic wire eliminates static electricity of the charged body, Here, some characteristics of the Electrically Conductive Fiber (ECF), recently developed by Teijin Limited,, were investigated. The resistivity of the ECF is about 10² - 10³ ohm per centimeter as shown in Table 1. In early stages of this research, it has become apparent that the ECF has the elimination faculty of static electricity and that the elimination mechanism depends upon the corona discharge. In this paper, the discharge characteristics for the ECF, so-called "current-voltage characteristics" of the corona discharge, are experimentally scrutinized in various conditions. Fig.8, Fig.11 and Fig.14 etc. give the examples of the experimental results in various kinds of electrostatic field. It has been, definitely shown by these results that
  (1) Static electricity of the charged body is approximately eliminated until the corona starting : voltage of the ECF.
  (2) The ECF has the elimination faculty of static electricity in low humidity as well as in high.
  (3) The elimination faculty of static electricity of the high electric resistance ECF, with the resistance more than 10⁹ ohm per centimeter, is not different from that of the low electric resistance ECF.
    A program is underway to ascertain the function of the ECF in eliminating the static electricity of cloth.

JNIOSH