18

EXPLOSION-PROOF COAL-CUTTING EQUIPMENT.

The manufacturer shall be permitted to attach to the motor frame a plate
inscribed as follows:

The size, material, and design of both caution and approval plates sh:
with the approval of the bureau,

‘The caution and statement of approval may be combined upon a sing
a suggested form for which is shown below:

PERMISSIBLE EXPLOSION-PROOF MOTOR (OR
EQUIPMENT).

Approval No. ——.

Issued to the ——————_——Company.

PERMISSIBLE EXPLOSION-PROOF COAL-CUTTING
EQUIPMENT.

Approval No.
Issued to the-—————Company.
CAUTION

The permissibility of this equipment depends on the
absence of any openings in the casings other than those
provided with protective devices by ihe manufacturer.

Cover plates should be screwed on tight aud the casings
frequently inspected for improper openings.

all meet

le plate,


EQUIPMENTS APPROVED AND DESCRIPTION OF TESTS. 33

When this investigation was well under way request was made for
the aproval of a 500-volt unit of the same type. The company was
not required to submit a complete 500-volt outfit but only a 500-volt
rheostat.

DESCRIPTION OF 23—-C DIRECT CURRENT EQUIPMENT.

The equipments covered by this investigation are designated as
Type 23-C short-wall mining machines. Approval No. 101 was as-
signed to the 210-volt unit and approval No. 101A to the 500-volt unit.

The electrical parts considered in granting the approvals were
the motor, the controller, the rheostat, the cable-reel and truck, in-
cluding fuse and switch, and the wiring. Plate VII, A, gives an
assembled view of the machine and Plate VII, 2B, a similar view of
the cable-reel and its truck. Drawing lists 101 and 101A, kept on
file by the bureau, give the essential details of construction upon
which approvals 101 and 101A, respectively, were based.

MOTOR.

The motor, Plate VIII, is a direct-current, multipolar, compound-
wound machine, designed to deliver 35 horsepower for one hour with-
out exceeding a rise of temperature of 75° C. on the windings on
100° C. on the commutator. The flanged cover @ that fits over the
commutator pit has two observation windows, 8, protected with
covers kept closed by springs.

CONTROLLER AND STARTING RHEOSTAT.

Plate VIII also shows the general location of the controller com-
partment. This compartment is closed with a flanged cover. ¢,
shown removed. The same plate presents a view of the rheostat com-
partment with the cover removed and a 210-volt rheostat, d, in-
stalled.

CABLE REEL AND TRUCK WITH FUSE AND SWTTCTI,

Plate VII, B, shows a two-wheeled truck upon which are mounted
the cable recl and an explosion-proof compartment containing a fuse
and a switch.

FUSE AND swrrert.

Plate IX shows details of the explosion-proof compartment, which
contains a fuse, a two-pole switch and connections to the cable reel.
The fuse @ is mounted in a holder which fits into the end of the cover,
6, of the explosion-proof compartment. The design is such that the
fuse must first be disconnected from the circuit before it can be
removed from the explosion-proof compartment. When assembled


EQUIPMENTS APPROVED AND DESCRIPTION OF TESTS. 31

the motor running. The effect of raising the covers of the explosion-
proof compartments ;; inch was also tried.

Tests were made to show the explosion-proof qualities of the cas-
ings that protect. the slip-ring contacts in the cable reel. These tests
were made in 8.6 and 7 per cent gas, with and without coal dust.

The cable-reel disconnecting plug, by which connection between
the machine and cable reel is made, was tested both in 8.6 per cent
gas and in air for explosion-proof qualities. Tests of this plug were
also made to determine whether the casing of the plug would become
charged and cause an electric shock.

The 250-volt fuse was tested in air by throwing it directly across a
250-volt, 200-kw., d. c. generator, in series with a small resistance
approximately equivalent to a double circuit of No. 4/0 wire 530
feet long.

EXPLOSION PRESSURES OBTAINED.

The maximum indicated pressures for the machine as first received
were as follows:
In the motor compartment__.

In the controller compartment.
In the slip-ring compartment of the cab

7.0 pounds per square inch
26.0 pounds per square inch
el.

35.0 pounds per square inch

With the design of machine as finally approved, the average maxi-
num pressures were:

In the motor compartment...-.-------—~ 42.0 pounds per square inch
In the controler compartment... 40.6 pounds per square inch

There was no change made in the design of the slip-ring compart-
ment of the cable-reel, therefore the maximum pressure remains the
same as above.

CHANGES IN DESIGN.

As a result of tests and inspection at the testing station, the ma-
chine as first approved included changes in design as follows:

1. A refillable fuse, explosion-proof and interlocked with the
controller, replaced the fuse in a separate oil-filled box.

2. Unbottomed bolt holes were eliminated.

3. Specially designed, insulated studs replaced soft rubber bush-
ings that were submitted for the protection of cables where they
entered explosion-proof casings.

4, Insulated strain clamps were used.

5. The communicating passage between the motor and starting-
box was enlarged.

Experience with approved machines in service brought about the
following additional changes in design:

187837°—20——3


36 EXPLOSION-PROOF COAL-CUTTING EQUIPMENT.

The construction of the cable reel in its final design was essentially
the same as the one first submitted, hence no further tests were
made.

CHANGES IN DESIGN,

The following important changes in design brought about through
inspections and tests were made:

1. Bell-mouthed bushings replaced flexible armor for cable intakes.

2. Insulated strain clamps for cables were provided.

3. The fuse box on the motor was eliminated.

4, Another opening between controller and motor compartments
was provided.

5. The outlet from the cable-reel protective device was shrouded
to prevent the entrance of dust and dirt.

INVESTIGATION OF 500-VOLT EQUIPMENT.

From an examination of the drawings submitted for the two equip-
ments the engineers in charge of the tests decided that it would only
be necessary to determine what effect would be produced upon the
pressures with the 500-volt rheostat installed as compared to the
pressures with a 210-volt rheostat. The 500-volt rheostat was in-
stalled in the 210-volt machine and tests were made with 8.6 per
cent gas, no coal dust, and with the motor running. Pressure read-
ings, taken in the rheostat compartment, were found to be slightly
less with the higher voltage rheostat than with the lower one. All
changes made as a result of the inspection and test of the 210-volt
equipment have been incorporated in the 500-volt equipment.

The approval of the 500-volt unit was based chiefly upon the
tests of the 210-volt unit.

SUMMARY,

Approvals No. 101 and 101A were both granted May 20, 1916.
When constructed in conformity with the machine tested and ap-
proved, the 23-C equipments are considered safe units and are
recommended for use in gaseous mines.

JEFFREY DIRECT-CURRENT COAL-CUTTING EQUIPMENTS, AP-
PROVALS NO. 102 AND 102A.

The Jeffrey Manufacturing Co., of Columbus, Ohio, made
application under Schedule 2 for the test and approval of a 250-volt
and a 500-volt equipment and submitted a 250-volt outfit for in-
spection and test. The investigation of the 250-volt equipment was
held to apply to the higher voltage machine because the mechanical
construction for either voltage was practically identical. The com-
pany was not required to submit a complete 500-volt unit. A 500-
volt rheostat, however, was shipped for inspection.


12 EXPLOSION-PROOF COAL-CUTTING EQUIPMENT.

The design and maintenance of safe protective devices is the clief
problem of apparatus of this class.

GENERAL RULES FOR CONSTRUCTION,

Apparatus for mine service should be especially strong and durable.
This insures that under the severe use to which it will be subjected
parts will not be distorted; that the mass will be rigid enough to
permit the construction of carefully designed, machined joints; and
that the casing will be strong enough mechanically to withstand any
pressure that might be developed by internal explosions.

All joints between sections of compartments or between covers and
compartments should be flanged joints. The surfaces of such flanges
should have at all points a minimum metal-to-metal contact at least
1 inch wide.

The joints of totally inclosed apparatus or of apparatus having one
or more totally inclosed compartments, require special consideration,
as the pressure developed in such apparatus during an explosion is
necessarily higher than in apparatus provided with relief openin;
Such joints must be held together with a sufficient number of bo
or studs properly spaced and strong enough to maintain a uniform
bearing. A small opening along the flange when such joints are prop-
erly designed does not necessarily make the apparatus dangerous, as,
owing to the smallness of the opening, the flames are cooled both by
contact with the flanges and by expansion as they pass to the sur-
rounding atmosphere.

CONSTRUCTION OF PROTECTIVE DEVICES.
WIRE GAUZE PROTECTION.

The earliest protective device known is wire gauze, used by Sir
Humphrey Davy and his contemporaries on the miners’ flame safely
lamp. From its long use on such lamps this type of protection is
well known, The gauze gives excellent protection for the small
volume of gas found in an ordinary flame lamp. especially if the
Jamp is provided with a shield that prevents direct impact of moving
currents of fire damp on the gauze.

Motors and other apparatus usually have much more unoccupied
space, and therefore require many layers of gauze of considerable
area. Owing to the lack of mechanical strength, ganze of this area
must have reinforcement in order that the device can withstand ex-
plosion pressures. The layers of gauze are nsually separated by
metal grids or punchings that serve as spacers and supports for the
gauze. When these grids are tightly bolted or riveted together the
gauze is held in place rigidly. The grids or punchings, also, abstract
heat from the flames.





*NOILO3dSNI YOJ N3dO SLNAWLYYdWOD YSTIONLNOD ONY HOLOW ‘SNIHOVW LNSYUNO-LOBYIG ase AawsSar

AX BLvid of NILaTING 83NIW 40 nvaune



40 EXPLOSION-PROOF COAL-CUTTING EQUIPMENT.

SUMMARY.

Approvals No. 102 and No. 102A were issued November 2, 1917.
When constructed in conformity with the machine tested and ap-
proved, the 28A equipments are considered safe units and are recom-
mended for use in gaseous mines.

JEFFREY DIRECT-CURRENT COAL-CUTTING EQUIPMENTS, AP-
PROVALS NO. 103 AND 103A.

The Jeffrey Manufacturing Co., of Columbus, Ohio, also ap-
plied under Schedule 2 for the test and approval of a second type of
direct-current equipment in two voltages, and submitted a machine
equipped with a 250-volt motor for inspection and test. Because
the 500-volt equipment was practically the same in mechanical
construction as the lower voltage equipment, one set of inspections
and tests was held to be sufficient for both voltages.

DESCRIPTION OF 35B DIRECT-CURRENT EQUIPMENTS,

The equipments covered by this investigation are known as Type
353, short-wall mining machines. The 250-volt direct-current equip-
ment was assigned approval No. 103 and the 500-volt equipment ap-
proval No. 103.4.

The motor, the controller, the rheostat, the cable reel, and truck
with fuse and switch, and the wiring were the electrical parts con-
sidered in granting the above approvals. The one design of con-
troller, resistances, and cable reel, fuse, and switch is used for either
the 28A or 35B machines. Plate XIV, A, shows an assembled view
of the machine proper, and Plate X, B, the cable-reel truck with reel,
fuse, and switch.

Drawing lists 103 and 103A kept on file with the bureau give tho
essential details of construction upon which approvals 103 and 103A,
respectively, were based.

MOTOR.

The 35B equipment is operated by a compound-wound multi-
polar motor designed to deliver 35 horsepower for one hour, with-
out exceeding a temperature rise of 75° C. The removable cast-steel
cover a (Pl. XV) gives ready access to the commutator and brush
holders.

CONTROLLER ANP STARTING RHEOSTAT.

Plate XV also gives a dissembled view of the type of controller
that is common to the 28A and 35B machines. The controller drum is
operated by the handwheel 6, the reversing switch by the handle ¢.

In the 35B machines the rheostat is placed in a compartment
which is embodied in the main frame. Plate XIV, B, shows the


BUREAU OF MINES BULLETIN 78 PLATE XVII

A. SULLIVAN CE-7 ALTERNATING-CURRENT MACHINE, MOTOR REMOVED;
REAR HEAD IN THE BACKGROUND AND CONTROLLER COMPARTMENT
OPEN FOR INSPECTION.

B, SULLIVAN CE-7 ALTERNATING-CURRENT MACHINE; SWITCH AND FUSE
COMPARTMENT OPEN FOR INSPECTION.




BUREAU OF MINES BULLETIN 78 PLATE XIII

A. JEFFREY 28A AND 35B DIRECT-CURRENT CABLE REEL AND SWITCH; COM-
PARTMENT FOR SWITCH WITH FUSE OPEN FOR INSPECTION.

B, JEFFREY 28A AND 358 DIRECT-CURRENT CABLE REEL AND SWITCH;
TERMINAL COMPARTMENT OPEN FOR INSPECTION.


22 EXPLOSION-PROOF COAL-CUTTING EQUIPMENT.

Plate I, A shows the chamber closed and the operator at one obser-
vation window about to witness a test; at his right is the firing
switch to which are connected flexible leads, a; & is the ignition line
from the spark coil. There are four of these observation windows
equally spaced around the cylinder. Plate I, B shows a closer view
of these windows and the shrouded hood for protecting the operator
from flames issuing from the top of the chamber. Canvas curtains
that fit over the hoods may be used to darken the interior and to en-
able the observer to see better the results of the explosion.. In this
view the cover or top of the chamber is shown raised in position for
airing out the chamber and also to permit the operator to enter and
to make necessary connections, changes, or inspection. When the gas
within the inclosure is exploded the pressure is released through the
oiled-paper heads a, Plate I, B. These heads are held in position by
iron rings, b, with rounded edges that fit closely in grooves. When
the gallery is not in use the heads are protected from the weather by
sheet-iron covers, The rim ¢ of the top sits in the channel d, when
the chamber is closed for test, and a gas-tight joint is obtained by
filling the channel with either grease or water.

FAN AND CIRCULATING SYSTEM,

Figure 1, a diagram of the testing apparatus, shows clearly the
arrangement of piping, valves, ete., of the circulating system, also
shown in part in Plate II, A. By means of this apparatus a uniform
mixture of gas and air may be obtained in the chamber as well as in
the motor or other apparatus under test. The mixture is discharged
into the bottom of the chamber at two diametrically opposite points.
These discharge points or outlets are about six inches from tho
cylindrical wall and are so formed as to give the mixture a rotary
motion, thus effectively mixing the gallery atmosphere with the en-
tering gas. The main suction line from the fan enters the chamber
floor near its center. By proper manipulation of valves an auxiliary
suction line is used when filling the machine to be tested with tho
explosive mixture,

SWITCHBOARD.

On the switchboard shown in Plate TI, 2 are mounted the con-
troller a, for operating the crane-hoist motor, and the switch mechan-
ism 6 that times the ignition with the release of the indicator drum
and the switch for operating the circulating fan and other circuits
connected with the testing gallery.

Below the switchboard are shown the chains ¢ that are used to
open and close valves in the piping conncetions of the apparatus
under éest, thus permitting the operator to fill one or more compart-
ments of the apparatus with the gaseous mixture,


34 EXPLOSION-PROOF COAL-CUTTING EQUIPMENT.

the circuit is closed through the fuse by turning the holder until
the blades, d, engage with the clips, e.

The casting, 7, serves both as a protecting cover for insulated studs
which complete the circuit through the casing of the compartment,
and also as the hell-mouthed bushing for the cable where it connects
with the insulated studs.

The switch is in the lower part of the compartment and is operated
by the handle, ¢.

SAFETY FEATURNS.

The 23-C machine is provided with the gauze and grid type of pro-
tective device. The machine itself has two protective elements (PI.
VIII, ¢) installed in the end plate of the motor compartment. Fig-

ure 8 is a diagram of the path the

= [- burned gases must traverse when

== = discharged from this compartment.

= The outlet from the protective de-

vices is on the under side of the

casting where it can not easily be-
come clogged with dust.

The explosion-proof compart-
ment on the cable-reel truck has a
protective device (Pl. IX, g) of
the same type as the ones used in
the machine. The discharge from
this device is also downward.

The protective devices each con-

Geeta oe G eapleslon oroat met of sist of 24 layers of 32 mesh brass

" me gauze made of No. 22 (B. & S.
gage) wire, These are supported and spaced by means of 25 grids
or punchings from No. 16 (U.S. gage) sheet steel.

All joints between the covers and the various compartments have
broad flanges, which are well secured with studs or bolts with bot-
tomed holes.

The inclosure of the switch and fuse in an explosion-proof com-
partment on the cable-ree! truck eliminates the danger of external
ignition of fire damp by sparks or flashes that are common when the
circuit is opened. The fuse plug can not be withdrawn from the ex-
plosion-proof compartinent unless it is first turned 90°. This turning
disconnects the fuse from the circuit and at the same time insures a
broad flange between the casing and the head of the fuse plug when
the circuit is opened.

The wiring between the motor, the controller, and the rheostat
compartments is within the machine proper and thus. is well pro-



PUBLICATIONS ON COAL MINING. 53

Tecrnica, Paper 20. Training with mine-rescne breathing apparatus, by
J.W. Paul. 1912. 16 pp. 5 cents,

TecHNicaL Paper 39. The inflammable gases in mine air, by G. A. Burrell and
F. M, Seibert. 1913, 24 pp., 2 figs. 5 cents.

TecuNicaL Paver 47. Portable electric mine lamps, by IL H. Clark, 1913. 8
pp. 5 cents.

‘TrounicaL Paper 56, Notes on the prevention of gas and dust explosions in
coal mines, by G. S. Rice, 1913. 24 pp. 5 cents.

‘TecrNica. Paper 67. Mine signboards, by Edwin Higgins and Edward Steidle,
1918. 15 pp. 1 pl, 4 figs, 5 cents.

‘TsenNicaL Pares 77. Report of the Committee ov Resuscitation from Mine
Gases, by W. H. Cannon, G. W. Crile, Joseph Erlanger, Yandell Henderson, and
S. J. Meltzer, 1914, 85 pp, 4 figs. 5 cents,

TecHNreaL Paver 101. Permissible explosion-proof electric motors for mines;
conditions and requirements for test and approval, by H. TZ. Clark, 1915. 14
pp., 2 pls., 1 fig. 5 cents,

Miners’ Cracurar 15. Rules for mine rescue and first-aid field contests, by
J. W. Paul. 1913. 12 pp. 5 cents.

O°


CONTENTS.

Equipments approved and description of tests—Continued.
Goodman direct-current coal-cutting equipments—Continued.
Investigation of 500-volt equipment.
Summary -.-___-
Jeffrey direct-current coal-

‘os. 102 and

tting equipments, approve

Controller and starting rheostat_.

Cable reel and truck with fuse and switch.

Safety features

Investigation of 250-volt “equipment.

Preliminary inspection and recommendations_.

Nature of tests.

Explosion pressures obtained_

Changes in design__.

Investigation of 500-volt equipment.

Summary -

Jeflrey direet-curvent coal-cutting equipment:
and 103A. =.

Description of

Motor __.

Controller and starting rheostat——-.

Cable reel and truck with fuse and sw

Safety features.

Investigation of 251 -

Preliminary inspection and recommendation

Nature of tests.

Explosion pre:

Changes in d

Investigation of

Summary ~.

Sullivan alternating-current coal-cutting equipments,

104 and 104A___.

Description of CE-7 alternating-current equipments.

Motor -~----------~-----.

Controller and fuse compartnients.

Cable reel__.

Safety features.

Investigation of 440-volt equipment__

Preliminary inspection and recommendation:

Nature of tests.

Explosion pressures obtained.

Changes in design.

Investigation of 220-volt equipment.

Summary —_.

Résumé ---.

Publication on coal mining

approvals

-B direct-current equipmen:

ures obtained...
esign____.
O-volt equipment_



BUREAU OF MINES BULLETIN 78 PLATE V

A, SULLIVAN CE-7 DIRECT-CURRENT CABLE REEL.

B, SULLIVAN CE-7 DIRECT-CURRENT CABLE REEL, PARTLY DISMANTLED FOR
INSPECTION,



SCHEDULES ISSUED FOR TESTING EXPLOSION-PROOF EQUIPMENT. 19

NOTIFICATION OF MANUFACTURER,

soon as the bureau’s engineers are satisfied that a motor is permissible for
use in places where gas may occasionally be present in explosive proportions,
the manufacturer shall be notified to that effect.

AS soon as a manufacturer receives formal notification that his motor has
passed the tests prescribed by the bureau, he shall be free to advertise such
motor as permissible and may attach approval plates to such motors.

DRAWINGS OF APPROVED MOTORS TO BE FILED,

As the safety of an explosion-proof motor depends largely on {ts construction,
the approval of a motor must identify the details of construction, on which the
approval is based. This {dentification will be accomplished by reference to a
list of drawings and photographs that describe in detail such parts as directly
or indirectly affect the safety of the motor or any of its accessories. Each list
of drawings will be given a number to facilitate reference, A copy of each
drawing will be filed with the Bureau of Mines,

SCOPE OF APPROVAL,

The bureau's approval of any motor shall be construed as applying to all
motors of that specific type, class, form, and rating, made by the same manufac-
turer, that have the same construction in the details directly or Indirectly af-
fecting the safety of the motor, but to no other motors.

Manufacturers shall, before claiming the bureau's approval for any modifica-
ton of an approved motor, submit to the bureau drawings that shall show the
extent and nature of such modifications, in order that the bureau may decide
whether test of the remodeled motor will be necessary for approval, Bach
approval of a permissible motor will be given a serial number,

WITHDRAWAL OF APPROVAL.

The bureau reserves the right to rescind for cause, at any time, any approval
granted under the conditions herein set forth,

TESTS OF STORAGE-BATTERY LOCOMOTIVES.

Storage-battery locomotives may be submitted for test under this schedule,
Their construction shall comply with the spirit of the general specifications for
motors,

The motors, controllers, and resistances of storage-battery locomotives shail
he explosion proof, and all interconnecting wiring shall be run in metallic con-
duit. The battery cells shall be installed in a locked inclosure which shall be
protected in a manner consistent with the spirit of the specifications for the
remainder of the equipment.

FEES FOR TESTING EXPLOSION-PROOF MOTOR!
AND LOCOMOTIV

COAL-CUTTING EQUIPMENTS,

‘The following fees to. he charged on and after the date of approval of this
schedule have been established and approved by the Secretary of the Interior:

ITEM 1, COMPLETE TESTS.

For an official investigation consisting of. 50 tests of an explosion-proof
motor or coal-entting equipment, to determine its pernnissibllity for use
in gaseous mines_ - $175



GAS AND EQUIPMENT USED. 25
DRAWINGS.

In those investigations connected with small apparatus, such as
flame or electric lamps, the bureau retains a sample of the lamp
tested as a permanent record, so that a comparison can be made at
any future time to determine whether the manufactured product has
changed. For coal-cutting equipment this practice evidently is not
feasible. In order, however, that the bureau. shall have a concise
record of the equipment tested, very complete drawings showing the
details of construction, materials used, and in every way identifying
the equipment approved are required. These drawings together
with photographs of the equipment make up a “ drawing list” kept
on permanent file with the bureau.

That modifications of the design will be necessary from time to
time is recognized, and the schedule takes care of such contingencies
by requiring the manufacturer to submit drawings that show the
extent and nature of such changes, in order that the bureau may
decide whether or not further tests are necessary.

As the approval covers only apparatus built in accordance with
the drawing list, which is revised to take in all authorized extensions,
of approval, any modifications made in the construction of approved
apparatus without the bureau’s knowledge renders the approval void.

In applying any schedule to the testing of commercial equipment,
points will come up that are not entirely covered by the schedule.
An endeayor is made to handle such points to the satisfaction of the
parties interested. The intent of a schedule is to direct investiga-
tions and give fundamental rules for testing and approving equip-
ment. The details for individual cases should be worked out with the
object of the approval system in mind, namely, the development of
equipment that will safeguard the life of the miner.

INSPECTION AND MAINTENANCE OF APPROVED EQUIPMENT.

-The burean’s tests cover only the examination and test of one equip-
ment. Neither funds nor men are available for establishing systematic
factory inspection of approved equipment. Therefore, the reliability
of approved equipment must rest to a considerable extent with. the
manufacturer, who is responsible for placing the permissible stamp
on each individual equipment. Some manufacturers, recognizing this
responsibility, have established special regulations that require a
rigid certified inspection of each approved equipment at the factory.
Such regulations promote safety and hence are highly commendable.

The bureau’s approval is based on satisfactory operation under
service conditions. As a result of field investigations additional
modifications have been recommended, and these recommendations



SCHEDULES ISSUED FOR TESTING EXPLOSION-PROOF EQUIPMENT. 21

GAS AND EQUIPMENT USED.
GAS.

Natural gas composed * approximately of 82 per cent methane, 16.4
per cent ethane, 1.5 per cent nitrogen, and a trace of carbon dioxide
was used in all tests. The term “gas” used in describing tests refers
to this natural gas.

The most explosive mixture? of such gas and air is in the propor-
tion of 8.6 to 91.4. Such a mixture also burns most rapidly and gives
off the greatest amount of heat.

TESTING EQUIPMENT.

This investigation was conducted chiefly with apparatus described
in detail in the report of the preliminary investigation. As tho
principles governing the tests were the same for both the old and new
equipments, the old equipment will not again be described. The
bureau, jointly with the Jeffrey Manufacturing Co., designed a new
testing outfit, which was built and installed as a gift to the bureau
by the manufacturers of explosion-proof apparatus.

The complete testing gallery consists of the following parts: 1, An
explosion chamber in which tests are made; 2, a fan-and piping s;
tem for mixing and circulating the explosive mixture in the explosion
chamber and in the equipment under test ; 3, a switchboard on which
is mounted the electrical controlling apparatus and wiring for direct-
ing the action of the gallery; 4, a crane surmounting the gallery
equipped with a 3-ton electric hoist ; 5, other miscellaneous apparatus,
including a gas meter for measuring the gas admitted, a pressure in-
dicator that can be attached to the casing of the apparatus to record
the pressure developed therein by the explosion, and spark plugs that
can be mounted in the apparatus to initiate explosions at desired
points.

EXPLOSION CHAMBER.

The explosion chamber consists of a cylindrica] steel tank with an
internal diameter of 10 fect and a height of 44 feet. The cylinder sits
in the recess of an iron channel ring embedded in a concrete base.
The joint between the bottom of the cylinder and the channel iron is
made gas-tight by a water seal.

«Hall, Clarence, Snelling, W. 0., and Howell, & P.. Investigations of explosives used
in coal mines, with a chapter on the natural gas used at Pittsburgh, by G. A. Burzedl,
and an introduction by C. E. Munroe, Bull, 13, Bureau of Mines, 1912, p. 66.
YMTall, Clarence, Snelling, W. O., and Howell, 8. T, Work cited, p. 77.
*Clark, H. H., Iuvestigation of exploston-proof motors, Ibull, 46, Bureau of Mines,
1912, 44 pp.



BUREAU OF MINES BULLETIN 78 PLATE VI

=

A, SULLIVAN CE-7 DIRECRT-CURRENT MACHINE, FRONT HEAD WITH ONE
ELEMENT OF PROTECTIVE DEVICE REMOVED.

B. SULLIVAN CE-7 DIRECT-CURRENT MACHINE, REAR HEAD WITH ONE.
ELEMENT OF PROTECTIVE DEVICE REMOVED.



16 EXPLOSION-PROOF COAL-CUTTING EQUIPMENT.

exterior of the motor casing, but must also possess sufficient mechanical
strength to insure against the accidental destruction of their prospective quali-
ties, If there are moving parts in connection with euch devices, these parts
should be so designed that there can be no interference with their movement.

All leads entering explosion-proof casings should pass through the casing in
the form of properly protected Insulated studs of approved design, The use
of rubber bushings will not be approved because the bushings may become dis-
placed and thus destroy the explosion-proof quality of the casing,

CONTROLTANG APPLTANCES.

Starting rheostats and other necessary equipment that may cause an igni-
tion of gas must be protected as adequately as the motor itself, The ca of
starting rheostats must be explosion proof. The resistances and contacts of
the starting rheostats used with portable motors of not more than 50-horse-
power capacity should be inclosed in the same box, unless inclosed in separate
boxes connected by approved piping through which all leads are carried,

The casing of the starting rheostat should be mouuted on the motor casi:
if possible, and the intercommunicating openings for the passage of leads
should be made large in order to prevent the rise of pr
tends the propagation of an explosion through a sms
partment to another.

Tf it is not possible to mount the starting rheostat on the motor frame, all
leads connecting the starter with the motor should be carried in rigid metallic
conduit.

Unless means for opening the cireuit both automatically and by hand are pro-
vided in a separate explosion-proof casing, they should be incorporated in the
design of the starting rheostat. If the starting switch is mounted on the frame
of the motor, provision should be made for entirely disconnecting the electric
circuit from the starting switch,

I hole from one com-

MOTOR CASTNG.

All joints in the casing of a motor or of any of its accessories must he metal-
to-metal joints with faces not less than 1 inch wide, and if the pressure de-
veloped in the motor easing by explosions exceeds 50 pounds per square inch
the faces must be not less than 1} inches wide, All bolt holes in casings must
be bottomed or so arranged that the accidental omission of a bolt will not give
an opening through the casing. All openings in the motor casing other than
those provided with protective devices by the manufacturers must be tightly
closed. It is desirable that such openings be as few as possible. There should
be uo exposed terminals or contacts outside the motor casing. If there are
glass-covered openings in the casing of a motor, the glass should be of ample
thickness and should be protected by strong metal covers that close automati-
cally unless held open by hand. Armature bearings must be so designed that
under no circumstances can an explosion be propagated from the interlor of the
motor casing around the armature shaft or through the oil wells,

CARLE RE

AND TRATTING CARLE.

If there are any sliding or rnbhing contacts in conection with the cable
reel, such con! should be provided with explosion-proof protection, and any
plug connections should be constructed so that they will be explosion proot.
At the point where the trailing cable enters or joins the frame of portable



44 EXPLOSION-PROOF COAL-CUTTING EQUIPMENT.

vided with two sets of contacts, one for the starting and one for the
running position. The controller wires d pass to the fuse compart-
ment on the opposite side of the machine through a narrow passage
so proportioned that the wires fit snugly and prevent an explosion
from propagating from one compartment to the other.

Plate XVII, B, gives a view of the reverse side of the machine and
shows the fuse compartment open for inspection. The current leaves
the reel by the cable-reel disconnecting plugs @ and by the hand cable
6 which enters the machine through the bell-mouthed bushing «
The current then passes through the three-phase switch d to the fuses
located on the same cover. One fuse ¢ is shown removed from the
cover. These fuses are interlocked with the switch so that they can
not be removed or inserted unless the switch is open. The cables f
run from the fuse terminals to the controller.

CABLE REEL.

The cable reel is essentially the same as for the d. c. machines pre-
viously described, except that it is built for a three-phase instead of
a two-wire circuit. Plate XVIII, B, shows one end of the three-
phase reel dismantled. This view gives clear details of the slip-ring
compartment. The trailing cable is connected to the movable con-
tacts a, which make contact with the stationary rings b. The cir-
cuit to the machine is completed by the cable reel disconnecting
the plugs ¢ and the hand cable d. The details of the disconnecting
plug have already been described for the d. c. equipment.

SAFETY FEATURES,

Plate XVI, B, shows the front head of the a.c. machine with both
clements of the protective device removed. The rear head has two
identical elements. The construction of the protective elements is
the same as for the d. c. machine, and the paths which the burned
gases must traverse when discharged through the devices to the
atmosphere is essentially the same as shown in figure 2 for the d. ¢.
machine,

The design of the disconnecting plugs for the reel is common for
a.c. and d. c, equipments and therefore should afford the same- pro-
tection, The three-phase switch is so interlocked with the fuses that
they can neither be withdrawn nor inserted unless the switch is open.

The fuse compartment in the a. c. outfits corresponds to the rheo-
stat compartment of the d. c, units. The fuse and controller com-
partments are practically isolated from each other and from tho
motor compartment in order to prevent the heaping ‘of pressure
caused by the propagation of the explosion from one compartment
to another,


8 EXPLOSION-PROOF COAL-CUTTING EQUIPMENT.

CONDITIONS NECESSARY FOR EXPLOSION.

The basic conditions that bring about a mine explosion having its
ignition from an electrical source are as follows: The presence of
fire damp in the immediate vicinity of the apparatus, the penetra-
tion by diffusion or otherwise of the fire damp into the apparatus,
and the ignition of the fire damp by an electric spark, flash, or other
means.

FACTORS BEARING ON SAFETY,

The hazard introduced with the use of a piece of electrical appara-
tus in a gaseous mine, and the possible results of an explosion within
that apparatus, depend upon the following factors: Lack of protec-
tion, weak mechanical construetion, incorrect ideas of what con-
stitutes adequate protection, the amount and arrangement of the
internal unoccupied space, the compression of the gas within the
machine, and the percentage of gas and the amount and distribution
of coal dust.

SPREAD OF EXPLOSIONS FROM UNPROTECTED APPARATUS,

If the explosion is caused by unprotected apparatus the mixture
surrounding the equipment. can reasonably be expected to ignite.
Such an outside explosion in an anthracite mine would proceed as
far as the gaseous mixture extended, and in a bituminous mine, due
to the explosibility of coal dust, it would probably continue through-
out the mine. In either event life and property may be lost.

SPREAD OF EXPLOSIONS FROM DAMAGED APPARATUS,

If the explosion takes place within apparatus of weak mechanical
construction, walls will be distorted or destroyed, bolts will be
sheared, seams and joints will be opened, and the explosion will
spread to the outside with the disastrous results t mentioned.
Much inadequate apparatus is used in mines, because many manu-
facturers do not realize the necessity of providing durable, rugged
equipment for all kinds of mine work. For safety devices good
mechanical construction is all the more necessary, The walls of such
apparatus must be strong enough to withstand internal-explosion
pressures so that no path will be made whereby the flames may eseape
throngh openings and ignite possible explosive mixtures outside.

SPREAD OF FEXPIOSIONS THROUGH! OPENINGS IN APPARATUS,

When overlooked or accidental openings, such as free space around
the wires where they enter the casing, a path throngh oil wells, or
a path caused by the omission of « bolt or cap-screw from an un-
bottomed hole, an internal explosion may possibly be propagated


EQUIPMENTS APPROVED AND DESCRIPTION OF TESTS. 29

and the connection within the extension 2 on the slip-ring housing e.
The blow-out coil is mounted within the shrouding cylinder (, which
has a bell-mouthed cable entrance, ec.

SAFETY FEATURES.

Plate VI, 4, shows the commutator end or front head with one
element of the double protective device removed from the head.
Plate VI, 2, shows a similar view of the gear end or rear head. Each
element is made up of 35 sheet steel punchings or plates 0.0187 inch
thick, which are separated by spacers of the same thickness, The
general construction of the plate type of protective device can be
seen by reference to Plate VI, A. The plates « are riveted between
the rings 6. The openings ¢ project downward as shown in figure 2
and prevent excessive clogging by coal dust. Figure 2 also shows the
paths that the burned gases must traverse when discharged through
the protective devices to the atmosphere.

All joints between compartments or between covers and compart-
ments have wide flanges secured by studs or bolts with bottomed
holes which preclude the possibility of a hole through the explosion-
proof casing due to the accidental omission of a bolt.

The fuse in the controller compartment is so arranged that it can
not be removed or replaced under load. The cable-ree] disconnecting
plug was developed as the result of experience with several unsatis-
factory designs. In its final form it proved, under extremely severe
tests, to be explosion-proof when the circuit was opened under load.

The wiring between the motor, the controller, and the rheostat
compartments is well protected as it is run within the machine. The
trailing cable is protected by bell-mouthed bushings where it enters
the main frame and the cable-reel plugs.

INVESTIGATION OF 250-VOLT EQUIPMENT,

A 250-volt equipment, comprising a motor, controller, rheostat, and
cable reel, was submitted for investigation.

PRELIMINARY INSPECTION AND RECOMMENDATIONS.

The preliminary inspection of the Sullivan d. c. equipment
revealed a number of unsatisfactory features.

Recommendations were made for changes in design of the fuse box,
the entrance of trailing cable to the machine, the method of securing
the starting-box cover, and the cable-reel parts.

NATURE OF TESTS.

The motor was tested in 8.6 per cent gas and in 7 per cent gas,
both with and without coal dust. Most of the tests were made with


PUBLICATIONS ON COAL MINING.

A limited supply of the following publications of the Bureau of
Mines has been printed and is available for free distribution until
the edition is exhausted. Requests for all publications can not be
granted, and to insure equitable distribution applicants are requested
to limit their selection to publications that may be of especial interest
to them. Requests for publications should be addressed to the
Director, Bureau of Mines.

The Bureau of Mines issues a list showing all its publications avail-
able for free distribution as well as those obtainable only from the
Superintendent of Documents, Government Printing Office, on pay-
ment of the price of printing. Interested persons should apply to
the Director, Bureau of Mines, for a copy of the latest list.

PUBLICATIONS AVAILABLE FOR FREE DISTRIBUTION.

Rutretin 17. A primer on explosives for coal miners, by C. E. Monroe and
Clarence Hall. 1911, 61 pp.. 10 pls. 12 figs.

SULLETIN 20. The explosibility of coal dust, by G. 8. Rice, with chapters by
J.C, W. Frazer, Axel Larsen, Frank Haas, and Carl Scholz. 1911. 204 pp.,
14 pls., 28 figs.

BULLETIN 42, The sampling and examination of mine gases and natural gas,
by G, A. Burrell and F. M. Seibert. 1918. 116 pp. 2 pls. 28 figs, 20 cents,

Burren 45. Sand available for filling mine workings in the Northern
Anthracite Coal Basin of Pennsylvania, by N. H. Darton, 1912, 38 pp.
8 pls, 5 figs.

Buuerin 46, An investigation of explosion-proof mine motors, by H. H.
Clark, 1912. 44 pp. 6 pls., 14 figs.

Bouerin 48, The selection of explosives used in engineering and mining
operations, by Clarence Hall and §. P. Howell. 1914. 50 pp.. 3 pls.. 7 1

Betrerm 50. A laboratory study of the Inflammability of coal dust, by
J.C. W. Frazer, B. J. Hoffman, and L, A. Scholl, jr. 1918. 60 pp., 95 figs.

B-LLETIN 52. Ignition of mine gases by the filaments of incandescent electric
lamps, by H. IL Clark and L. G. Tsley. 1918. 31 pp., 6 pls, 2 figs.

Burterm 56. First series of coul-dust explosion tests in the experimental
mine, by G. 8. Rice, L. M. Jones, J. K, Clement, and W. L. Egy. 1913. 115 pp,
12 pls. 28 figs.

Burietin 57, Safety and efficiency in mine tunneling, by D. W. Brunton and
J. A. Davis. 1914, 271 pp., 6 pls., 45 figs,

Burserty 60. Hydraulic mine filling, its use in the Pennsylvania anthracite
fields, a preliminary report, by Charles Enzian. 1913. 17 pp., 3 pls., 12 figs.

Buttery 62, National mine reseue and first aid conference, Pittsburgh, l’a.,
September 23-26, 1912, by HL. M. Wilson, 1913. 74 pp.

4a


PUBLICATIONS ON COAL MINING. 51

TECHNICAL Paver 103. Organizing and conducting safety work in mines, by
H. M. Wilson and J. R. Plemin; 1917. 57 pp., 35 figs.

TecHNican Paper 108. Shot firing in coal mines by electricity controled from
the outside, by H. H. Chirk, N, V. Breth, and CG, M. Means, 1915. 36 pp.

Teewnrear Taree 112. The explosibility of acetylene, by Go A. Burrell and
G. G. Oberfell, 1915. 15 pp.

TECHNICAL Paper 119. The limits of infammability of mixtures of methane
and uir, by G. A. Burrell aud G, G. Oberfell, 10915. 30 pp., 4 figs.

Tecrnicar, Paver 121. Effects of temperature and pressure on the explosi:
bility of methane-air mixtures, by G. A. Burrell and I. W. Robertson. 1916.
14 pp., 3 figs.

TECHNICAL Papen 122. Effects of oxygen deficiency on small animals and on
men, by G. A. Burrell and G. G. Oberfell, 1915. 12 pp.

TecuNican Paver 132. Underground latrines for mines, hy J. H. White. 1916.
28 pp., 2 pls., 7 figs.

TecHNtcaL Paper 134, Explosibility of gases from mine fires, by G. A. Bur-
rell and G. G. Oberfell. 1916. 31 pp., 1 fig.

TecuNtcar Parer 188. Suggested safety rules for installing and using elec-
trical equipment in bituminous coal mines, by H. H. Clark and ©. M. Means.
1917. 36 pp.

Tecuxicat, Paver 169. Permissible explosives tested prior to January 1.
1917, by S. P. Howell. 1917. 19 pp.

*TecuNicar, Paper 174, Suggestions for the safe operation of gasoline engines
in mines, by R. H. Kudlich and Edwin Higgins. 1917. 19 pp., 3 figs.

‘TECHNICAL Pareg 226. Men who received Bureau of Mines certificates of
mine rescue training, compiled by D. J. Parker. 1919. 72 pp.

Minexs’ CixcuLas 4, The use and care of mine reseue breathing apparatus,
by J. W. Paul. 1911. 24 pp., 5 figs. 5 cents,

Miners’ Circunsr 5. Electrical accidents in mines, their causes and preven-
tion, by H. H. Clark, W. D. Roberts, L. C. Isley, and H. F, Randolph, 1911. 10
pp., 3 pls.

Miners’ Circutak 7. Use and misuse of explosives in coal mining, by J. J.
Rutledge, with a preface by J. A. Holmes, 1913, 52 pp., 8 figs.

Miners’ Crrcurar 9. Accidents from falls of roof and coal, hy G. S. Rice.
1912. 16 pp.

Miners’ Craceiar 10. Mine fires and how to fight them, by J. W. Paul. 1912.
14 pp.

Muvexs’ Crectnar 11. Accidents from mine cars and locomotives, by TL. M.
Jones. 1902. 16 pp.

Mrers’ Crcunar 12. Use and eare of miners’ safety lamps, by J. W. Paul.
1913. 16 pp. 4 figs.

Mrxges’ Crrcutar 18. Safety in tunneling, by. D. W. Brunton and J. A. Davi
1913. 19 pp.

Miners’ Crrovnar 14, Gases found in coal mines, by GA. Burrell and F. M.
‘ibert. 1918. 23 pp.

Miners? Crecutaz 16. Hints on coal-mine ventilation, by J. J. Rutledge.
1914. 22 pp.

Miners’ Ctrcurar 18. Notes on miners’ carbide lamps, by
11 pp.

Miers’ Crrcunar 21, What a miner can do (o prevent explosions of gas
of coal dust, by G. S. Rice. 1915. 24 pp.

Mrngss’ Circular Dangerous and safe practices in bitumiuous coal
mines, by Edward Steidle. 1919, 110 pp., 181 figs,

TW. Paul 1915,

and



52 EXPLOSION-PROOF COAL-CUTTING EQUIPMENT.

Miners’ Crecutar 23. Elementary first aid for the miner, by W. A. Lynott
and D. Harrington, 1916. 24 pp., 19 figs.

Rescue and recovery operations in mines after fires and explosions, by J. W.
Paul and W. M. Wolflin. 1916. 109 pp.

Advanced first-aid instructions for miners, a report on standardization, by a
committee of surgeons: G. H. Halberstadt, A. F. Knoefel, W. A. Lynott, W. S.
Rountree and M. J. Shields. 1917. 142 pp., 65 figs.

PUBLICATIONS THAT MAY BE OBTAINED ONLY THROUGH THE SUPERIN-
TENDENT OF DOCUMENTS.

BuLetin 10, The use of permissible explosives, by J. Rutledge and Clar-
ence Hall, 1912. 84 pp., 5 pls,, 4 figs. 10 cents.

Butteriw 25. Mining conditions under the city of Scranton, Pa., report and
maps, by William Griffith and E. T. Conner, with a preface by J, A. Holmes
and a chapter by N. H. Darton. 1912. 89 pp., 29 pls. 50 cents.

Butrettn 26. Notes on explosive mine gases and dusts, with especial refer-
ence to explosions in the Monongah, Darr, and Naomi coal mines, by R. T.
Chamberlin, 1912. 67 pp., 1 fig. 10 cents.

Burietx 44, First national mine-saféty demonstration, Pittsburgh, Pa.,
October 30 and 31, 1911, by H. M. Wilson and A. H. Fay, with a chapter on
the explosion at the experimental mine, by C. Rice, 1912. 75 pp., 8 pls.
4 figs. 15 cents.

Beuitettw 61. Abstracts of current decisions on mines and wining, October,
1912, to March, 1913, by J. W. Thompson. 1913. 82 pp. 10 cents.

Butzettn 72. Occurrence of explosive gases in coal mines, by N
1915. 248 pp. 7 pls., 38 figs. 35 cents.

Buiretin 79. Abstracts of current decisions on mines and mining, March to
December, 1913, by J. W. Thompson. 1914. 140 pp. 20 cents.

Butrettn 82. International conference of mine experiment stations, Pitts-
burgh, Pa., September 14-21, 1912, compiled by G. S. Rice. 1914. 99 pp. 15
cents.

Buttery 83. The humidity of mine air, with especial reference to coal mines
in Ulinois, by R. Y. Williams, 1914. 69 pp., 2 pls., 7 figs. 10 cents.

Butietin 94. United States mining statutes annotated, by J. W. Thompson.
1915. 1772 pp. In two parts, not sold separately. Cloth, $2.50 per set;
paper, $2.

FLevIN 1138. Abstracts of current decisions on mines and mining, May to
ember, 1915, by J. W. Thompson. 1916. 72 pp. 10 cents.

Burserin 143. Abstracts of current decisions on mines and mining, May to
August, 1916, by J. W. Thompson. 1916. 72 pp. 10 cents.

Buwretin 147. Abstracts of current decisions on mines and mining, Septem
ber to December, 1916, by J. W. Thompson. 1917. 84 pp. 10 cents.

BuLierin 152. Abstracts of current decisions on mines and mining, January
to April, 1917, by J. W. Thompson. 1917, 79 pp. 10 cents.

BULLETIN 159. Abstracts of current decisions on mines and mining, May to
August, 1917, by J. W. Thompson. 1917. 111 pp. 15 cents.

TrcHNIcaL Paper 18. Gas analysis as an aid in fighting mine fires, by G. 4.
Burrell and F, M, Seibert. 1912. 16 pp. 1 fig. 5 cents.

TacANTCAL Pape 14. Apparatus for gas-analysis Iaboratories at coal mines,
by G. A. Burrell and F. M. Scibert. 1918. 24 pp., 7 figs. 5 cents.

‘Tecwntcar. Paper 24. Mine fires, a preliminary study, by G. S
Bl pp., 1 tig. 5 cents.

H. Barton.

Rice, 1912.


28 EXPLOSION-PROOF COAL-CUTTING EQUIPMENT.
DESCRIPTION OF CE-7 DIRECT-CURRENT EQUIPMENTS,

The equipments covered by this investigation are designated as
Type CE-7 continuous-cutting chain machines designed for room-
and-pillar work, Approval No. 100 was assigned to the 250-volt d. c.
equipment and 100A to the 500-volt unit of the same type.

The electrical parts considered in granting the approvals were the
motor, the rheostat, the controller and fuse, the cable reel, and the
wiring. Plate ITI, A, shows the assembled machine and Plate V, 4,
shows the assembled cable reel.

Drawing lists 100 and 100A, kept on file with the bureau, give the
essential details of construction upon which approvals 100 and 100A,
respectively, were based.

woror,

The motor used with these equipments is a direct-current, multi-
polar, compound-wound machine designed to deliver 80 horsepower
for one hour without exceeding a temperature rise of 75° C. Access
to the brush holders and commutator is provided by a flanged cover
directly over them.

CONTROLLER AND STARTING REHOSTAT.

Plate III, 2, shows the back of the controller « removed from the
eompartinent 4, This controller is fastened to the flanged cover ¢,
which is securely bolted to the main casting by means of the studs d.
The fuse plug e is inserted in the cover ¢ and is so interlocked with
the controller that the controller handle must be in the extreme
“off” position before a fuse can be removed or replaced. The con-
troller is equipped with magnetic blow-out coils.

The bell-mouthed bushing / serves as the entrance of the cable to
the machine.

Plate IV shows the machine in a reversed position, with the
rheostat cover removed. As the rheostat @ is installed within the
main casting it is well protected from mechanicel injury. The cables
connect with the motor throngh the passage ¢ in the rear head.

CABLE REI

The cable recl is mounted on an extension of the power car or truck
that is used for transferring the machine proper from place to place.
In Plate V, A, are shown the cable reel and disconnecting plugs by
means of which connection is made between the machine and cable
reel. One of these plugs is shown in service position in Plate V, B,
the other is seen partly dismantled. A brass sleeve, @, contains a
magnetic blow-out coil, which prevents an ave from being drawa
into the atmosphere when contact is broken between the brass sleeve



APPROVED EXPLOSION-PROOF COAL-CUTTING EQUIPMENT.
By L. C, Insney and E. J. Guer.

INTRODUCTION.

Electrical apparatus because of its flexibility and its adaptability
to all classes of service has become essential to the mining industry.
Hence the problem of providing electrical equipment that is safe for
use in explosive mixtures of methane and air is of prime importance
in coal mining. Investigators and experiment stations early recog-
nized this fact and much work has been done in the investigation and
the development of electrical apparatus for use in atmospheres con-
taining fire damp. The term “fire damp” as applied throughout
this bulletin means an explosive mixture of methane and air.

Direct-current motors and alternating-current motors of the slip-
ying type when running usually give off electric ares or flashes that
will ignite fire damp. Other motors that have no moving electric
contacts may become dangerous through accident, deterioration, or
neglect. Auxiliary apparatus such as fuses, switches, rheostats, and
controllers may arc, flash, or become heated to such a degree that fire
damp can be ignited. Such equipment is still more dangerous when
worn or out of repair.

In the United States the development of apparatus for use in
gaseous mines has been associated largely with coal-cutting equip-
ment run by electricity. This is undoubtedly due to the use of
such equipment at the face of the mine workings, where the chance
of igniting fire damp is necessarily greatest. One American manu-
facturer built a coal-cutting equipment of the totally inclosed type
for use in fire damp atmospheres in 1903. Another built similar
equipment with special protective devices in 1906, for export.

During the years 1910 and 1911, the Bureau of Mines at its Pitts-
burgh experiment station conducted a preliminary investigation of
the safety of such protection as was then in use or under considera-
tion. Five motors were submitted for this investigation, each having
somewhat different metliods of protection. The results of this in-
vestigation were published in Bulletin No. 46.

Clark, II. Ii, Investigation of exploson-proof motors, Bull, 46, Burcau of Mines,
1912, 44 pp.

5


ILLUSTRATIONS.

Prats i. A, Explosion-proof motor testing gallery closed for tests;
B, Gallery open for airing.

IL, A, Circulating fan with motor and parts of piping system;

B, Switchboard and control appliances. -
, Sullivan CE~7 direct-current machine; B, Sullivan CE-7
direct-current machine, motor removed and controller com-
partment open for inspection__.
IV, Sullivan CE-7 direct-current machine, rear lead removed to
the right and rheostat compartment open for inspection.
A, Sullivan CE-7 divect-current cable reel; B, Sullivan CE~
direct-current cable reel. partly disinantted for inspection_
A, Sullivan CE-7 direct-current machine, front head with one
element of protective device removed; B. Sullivan CE-7 di-
current machine, rear head with one element of protec-
tive device removed

VIL. 4, Goodman 23-C direct-c
direct-current cable reel and truck. - -

VIL. Goodman 23-C direst-current machine, open for inspection of
rheostat, controller, armature, and protective devices.

IX. Goodman 23-C direct-current cable recl aud truck, explosion
proof compartment open to show underside of protective de-

vice grid und details of switea and fuse.

X. A, Jeffrey 28-A direct-current machine; 8, Jeffrey cable reel
and switch for 28-A and 35-B direct-current machine:

rent machine; B, Goodman, 23-C

XI. Jeffrey 2S-A direct-current machine. Details of construction__
NIL. Jeffrey 28-A direct-curremt inachine, Further details of con-

struction
XIIL A, Jeffrey 28-A and 35-B direct-current cable reel and switch.
Compartment for switch and fuse open for inspection; B,
Jeffrey 28-A and 35-B divect-current cable reel and switeh;
terminal compartment open for iuspection_.
Jeffrey 85-B direct-curreut machine; B, Jeflrey 35-1 direct-
current machine; rheostat compartment open for inspection.
XV. Jeffrey 85-B direct-current machine, motor and controller com-
partments open for inspection -
A, Sullivan CE-7 aiternating-current machine; B, Sullivan
CE-7 alternating-current machine; front head with both
clewents of protective device removed...
XVIL 4, Sullivan CE-7 akernating-current machine. motor removed;
rear head in the background and controlier compartment open
for inspection. B, Sullivan CE-7 alternating-current inachine;
switch and fuse compartment open for inspection_
XVII 4, Sullivan CR-7 alternating-carreut machine; B, Sullivan
CE-7 alternatingcurrent cable reel dismantled to show
interior of slip-ring compartment and details of disconnect-
ing plag_
Fieurs 1. Elevation of testing apparatus
2, Paths of burned gases discharged through protective dev

of Sullivan CL-7 explosion-proof motors___
8. Path of burned gases discharged through pr
of Goodman 28-C explosion-proof wotor_

NIV. ¢

Page,
22

23

23

29

30

43

44
23

30

a4


SCHEDULES ISSUED FOR TESTING EXPLOSION-PROOF EQUIPMENT. 17

electric equipment, there shall be provided means for minimizing abrasion and
preventing short bends from occurring in the cable. There shall also be pro-
vided an insulated clamp of approved design for securely fastening the cable
and taking all mechanical strains that may be put on it.

CHARACTER OF TESTS TO WHICH MOTORS WILL BE SUBJECTED.

In testing a motor to establish its permissibil the motor casing will be
filed and surrounded with the most explosive misture of Pittsburgh natural
gas and air, The motor will then be operated at its rated speed and the mix-
ture within the casing ignited by a spark plug, by a spark from the motor
brushes, or by any other means that simulates the conditions of actual practice.

Similar tests may also be made with greater and with less amounts of gas
in the explosive mixture and with coal dust sifted into the motor casiig or
into the protective devices.
s will also be made to determine the point of ignition that gives the

reatest pressure, and tests will be made by igniting from such 2 point. Not
less than 50 tests of all kinds will be made, and more than that number may
be made if, in the opinion of the bureaw’s engineers, more tests are necessary
to prove the permissibility of the motor. In order that a motor shall pass
these tests, it shall in none of them cause an ignition of the gas surrounding
the motor or discharge flames from any part of the motor casiug. Neither
shall the motor develop dangerous afterburning® or excessive pressure in the
casing of the motor or its starting rheostat.

Even after having passed the tests just described, motors or equipments
will not be regarded as permissible if used under any of the conditions out-
lined below:

If used without the caution plate mentioned hereafier.

If used with openings in the motor casings other than those openings pro-
vided with protective devices by the manufacturer. This condition refers to
all openings but espectally to removable covers.

If the motor or equipnient when in operation is not complete with all of the
parts considered in the approval of the motor or equipment.

CAUTION AND APPROVAL PLATES

As part of the protection of a permissible motor, the manufacturer shall
be required to attach to the motor frame a metal plate inscribed us follows:

SAUTION.

‘The permissibility of this motor depends on the absence
of any openings in the casing other than those provided
with protective devices by the manufucturer.

Cover plates should be screwed on tight and the casings
frequently inspected for improper openings.

©The term “afterburning ” us used in this schedule is applied to the combustion, Im-
mediately after an explosion within an explosion-proof casing, of a gaseous mixture that
was not within the casing at the time of the explosion, but was drawn in subsequently
while the produets of the explosion were cooliug,



THEORY OF FIRE DAMP PROTECTION. 7

of abnormal quantities of gas, enough methane accumulates in a
given place to make the atmosphere of that place explosive.

EXPLOSIVE LIMITS OF FIRE DAMP,

The lower explosive limit of methane“ is reached when the pro-
portion is about 5.5 per cent of methane mixed with 94.5 per cent of
air. The upper explosive limit is about 14.5 per cent of methane to
85.5 per cent of air. Below or above this explosive range the methane
is only partly burned when the mixture is ignited.

Percentages of methane under 5.5 per cent, when mixed with large
volumes of coal dust in suspension, make a mine atmosphere more
dangerous than when it contains coal dust alone.

IGNITION TEMPERATURE OF METHANE,

Methane is ignited at about 650° C.2 This gas does not ignite
as readily as hydrogen and several other gases, but must be heated
to ignition temperature for an appreciable time before it ignites.
Therefore, flames of somewhat higher temperature than that at
which methane ignites may momentarily pass into this gas without
catising an ignition. However, the temperature resulting from sparks,
flashes, incandescent filaments, or other electric activity usually so
far exceeds the ignition temperature of methane (650° C.) that when
fire damp is present an explosion is almost sure to result.

PRESENCE OF FIRE DAMP IN ELECTRICAL APPARATUS.

Fire damp is likely to enter the interior of electrical apparatus that
has openings of sufficient size to permit diffusion of the methane with
the air, his diffusion will take place readily if the apparatus is
allowed to remain in a room filled with fire damp for several hours,
Apparatus of the totally-inclosed type is much less liable to be a
source of danger through diffusion of methane than apparatus of the
former type. Diffusion, however, is not the only way in which fire
damp enters the interior of apparatus. The metallic parts of elec-
trical apparatus are subject to variations of temperature during
periods of rest and operation, Consequently the atmosphere within
expands and contracts, creating an unbalanced pressure with the
atmosphere outside. This difference of pressure tends to become
equalized by the transfer of gases in and out of the casing. Thus fire
damp may be drawn into the interior of an electric motor, or other
electric equipment, through very small openings.

«Burrell, G. A. and Oberfell, G, G., The limits of inflammability of mixtures of
methane and air, Tech, Paper 119, Bureau of Mines, 1915, p. 30, Burrell, G. A, and
Gauger, A. W., Limits of complete inflammability of mixtures of mine gases and of in-
dnstrial gases with air, Tech, Paper 150, Bureau of Mines, 1917, p. 1

° Dixon, IT. B, and Coward, Th, F., ‘The ignition temperatare of gases, Chem. News,
Murch 19, 1909, vol. 99, p. 139.



23

GAS AND EQUIPMENT USED.

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Bulletin 78
DEPARTMENT OF THE INTERIOR
FRANKLIN K. LANE, Secretary
BUREAU OF MINES
VAN. H. MANNING, Drrzcror

APPROVED EXPLOSION-PROOF
COAL-CUTTING EQUIPMENT

BY

L. C. ILSLEY anp E, J, GLEIM

WASHINGTON
GOVERNMENT PRINTING OFFICE
1920


"NOILONYLSNOD JO STIVL3G 'ANIHOVI LNSYYND-LOaNIG vs~ ATussar

IX aLvid 82 NILaTINE S2NIW 40 nvauna


10 EXPLOSION-PROOF COAL-CUTTING EQUIPMENT.

slight compression of the interior mixture by centrifugal force, the
pressure produced by the explosion will usually be greater than that
obtained when the motor is stationary. Sometimes the external
gases are drawn into the motor interior immediately after an ex-
plosion and continue to burn. This action is usually termed “ after-
burning.” If afterburning is prolonged it will seriously damage the
insulation,

When the explosive mixture is composed of methane and air only,
reasonably consistent results, so far as flame and explosive pressure
are concerned, may be obtained, provided care is used to ignite from
a given point a definite mixture that is uniformly distributed
thronghout the interior of the apparatus. The pressure at any given
point within the apparatus. will depend on where the explosion was
initiated, and, to a certain degree, on proximity to relief openings.
At different points the pressure is greater or | depending on the
distance the flame has traversed before reaching that point and on
the arrangement of the internal unoccupied space.

Tf the explosive mixture in the inclosure contains between 8 and 9
per cent of methane, the explosion will be most violent, but not neces-
sarily most liable to cause an exterior explosion,? as experiments have
demonstrated that a lower percentage of gas will cause flames to pass
more easily through holes or gauze-type protective devices.

EFFECT OF COAL DUST IN TIE APPARATUS.

Coal dust may be present in the gaseous mixture as a dust cloud,
the density of which is a variable quantity and difficult. to measure
or duplicate under commercial testing conditions. Or the dust may
be in the form of a deposit, various amounts of which may be stirred
up by the force of the explosion. Some of these coal particles are
distilled, some are decomposed and enter into the combustion, some
are driven out through the openings in an incandescent state. Tests
made by the Bureau of Mines have not definitely shown that the
presence of coal dust within the apparatus increases the danger of
explosion, In some tests the pressure was increased. Undoubtedly
the decomposition of the constituents of coal abstracts heat from the
gas flames and cools them. If a dust cloud of just the proper density
were present, it might conceivably increase the combustion and con-
sequently the pressure.

In certain designs of protective devices the coal dust partly blocks
the exhaust openings and increases the pressure. When incandescent.

von Beyling, —, Versuche 2wecks Erprobung der Schlagwettersicherhelt besonders
geschillzter elektrischer Motoren und Apparate sowle aur Ermittlong geelgneter Schiitz-
yorrichtungen fnr solche Retrietsmittel. Ausgefiiurt auf der berggewerkschaftlichen
Versuehstrecke in Gelsenkirchen, 1908, 89 pp.


THEORY OF FIRE DAMP PROTECTION, 9

through these accidental openings to the outside atmosphere with the
disastrous effects already mentioned.

An explosion within electric apparatus may also be propagated
through intentional openings, such as relief openings and small open-
ings between flange joints, if such openings are not properly designed
so as to cool the escaping flames below the ignition temperature of
fire damp.

EFFECT OF INTERNAL SPACING ON INTERNAL PRESSURE,

Not only is the strengthening of the walls and relief openings of
the apparatus necessary, but particular attention should also be given
to the arrangement of the internal unoccupied space. If the explo-
sion begins at one end of a long passage, a pressure wave will precede
ihe flame wave. As this wave advances the rapidity of combustion
of the gases increases with the increase in pressure and further in-
creases the compression of unburned gases ahead, so that when the
flame wave reaches the other end of the passage the explosive mixture
there is under so much pressure that when it is ignited ordinary
casings will not be strong enough to withstand the resulting pressure.

The same is true if two or more compartments are connected. espe-
cially when the opening between the compartments is such as to create
a considerable pressure wave in advance of the flame propagation.
Therefore, long drawn-out paths should be avoided as they affect the
safety of the walls and as the violence of the flame propagation may
be such as to force the flames through the protective devices or the
flange joints.

EXPLOSION PRESSURES OF MIXTURES OF GAS AND AIR,

The physics department of the Bureau of Mines investigated the
effect of compression when explosive mixtures of natural gas and
air are ignited,

A mixture containing about 8 per cent of natural gas (of the com-
position given on page $2) under atmospheric pressure in a small steel
chamber gave a maximum pressure of 74 pounds to the square inch as
measured by a Crosby gas engine indicator.

A mixture having the same percentage of gas, but under 10 to 12
pounds above atmospheric pressure, gave a maximum pressure of
about 135 pounds to the square inch,

Although the above results are based.on special conditions, and
slight changes in temperature, size or shape of the chamber would
cause considerable difference in pressures, yet with other conditions
constant, a slight: increase in pressure plainly has a marked effect on
the violence of the explosion.

Suppose the explosion takes place in a compartment where parts,
such as the armature of the motor, are in rotation, then, because of the



EQUIPMENTS APPROVED AND DESCRIPTION OF TESTS. 43

tigation in order to bring it to the final approved form. Approval
No. 108A was based, in the main, upon the investigation of the
250-volt equipment.

SUMMARY.

Approvals No. 103 and No. 103A were issued November 2, 1917.
When constructed in conformity with the machine tested and ap-
proved, the 35B equipments are considered safe units and are rec-
ommended for use in gaseous mines.

SULLIVAN ALTERNATING-CURRENT COAL-CUTTING EQUIPMENTS,
APPROVALS NO, 104 AND 104A.

The Sullivan Machinery Co., of Claremont, N. H., also made ap-
plication under Schedule 2 for the test and approval of a 220-volt
and a 440-volt a. c. equipment and submitted a machine built for
440-volt service for inspection and test.

The investigation of the 440-volt equipment was held to apply to
the lower voltage outfit, since the mechanical construction for the two
voltages was practically identical.

DESCRIPTION OF CE-7 ALTERNATING CURRENT EQUIPMENTS.

The equipments covered by this investigation are designated as
Type CE-7 continuous cutting chain machines designed for room and
pillar work. . Approval No. 104 was assigned to the 220-volt a. c.
equipment and approval No. 104A to the 440-volt outfit.

The electrical features considered in this investigation were the
motor, the controller, the fuse, the switch, the cable reel, and the wir-
ing. Plate XVI, A, gives an assembled view of the machine proper
and Plate XVITI, A, an assembled view of the cable reel.

Drawing lists 104 and 104A, kept on file with the bureau, give the
essential details of construction upon which approvals 104 and 104A,
respectively, were based.

Moror.

The motor is a squirrel-cage. 3-phase, 60-cycle induction motor de-
signed to deliver 30 horsepower for 1 hour without exceeding a
temperature rise of 75° C. The winding of the stator is arranged so

that the motor can be started at about half voltage and then thrown
to full voltage for operation without rheostat control.

CONTROLLER AND FUSE COMPARTMENTS.

Plate XVIT, A, shows the machine with motor removed, rear head
in background, and controller compartment open for inspection. The
controller @ is fastened to the flanged cover 4, which in turn is held
securely to the main casting by the studs «. The controller is pro-




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EQUIPMENTS APPROVED AND DESCRIPTION OF TESTS. 37

DESCRIPTION OF 28A DIRECT-CURRENT EQUIPMENTS.

The equipments covered by this investigation are designated as
Type 28A machines for short-wall mining. Approval No, 102 covers
the machine which is equipped with a 250-volt motor and No. 1024
covers the same type of.machine having a 500-volt motor.

The electrical features considered in granting the above approvals
were: The motor, the controller, the rheostat, the cable reel and
truck with fuse and switch, and the wiring. Plate X, A, shows the
machine completely assembled and Plate X ,B, shows an assembled
view of the cable reel and truck.

Drawing lists 102 and 102A kept on file with the bureau give
the essential details of construction upon which approvals 102 and
102A, respectively, were based.

MOTOR

The 28A machine uses a direct-current, compound-wound, multi-
polar motor (Pl. XI, and Pl. XII), designed to give 35 horsepower
for one hour without exceeding a temperature rise of 75° C. The
cast-steel cover a (Pl. XI) is directly over the commutator when the
machine is assembled and is easily removed for examination. of
brushes and commutator.

CONTROLIER AND STARTING RHKOSTAT.

The controller is located in a two-part flanged casing bolted to
the casting of the main frame. Plate XII shows one part, a,
of the casing at the right. The arc barriers, 6, that separate the
contact fingers, are taken out to permit examination of the controller
drum, connections, and contacts.

The rheostat is in a separate compartment, ¢, Plate XII, and
connection between motor and rheostat are made through the pas-
sage, d. Plate XI shows the two types of resistance used in 281
machines. The compartment cover 6 has been taken off to show a
500-volt rheostat, c, bolted in place. A 250-volt rheostat, d, rests upon
the top of the compartment. The part ¢ protects the insulated studs
which connect the power supply to the interior of the machine. This
part also has a bell-mouthed bushing to prevent undue abrasion of the
cable.

CABLE REEL AND TRUCK WITH FUSE AND SWITCH,

A part of the cable-reel truck is shown in Plate X, B. On it are

mounted the reel and an explosion-proof fuse and switch compart-
ment.

The details of the explosion-proof compartment jnclosing a single-
pole switch and a fuse are shown in Plate XIII, 4. The switch


BUREAU OF MINES BULLETIN 78 PLATE IIL

A, SULLIVAN CE-7 DIRECT-CURRENT MACHINE.

B. SULLIVAN CE-7 DIRECT-CURRENT MACHINE, MOTOR REMOVED AND CON-
TROLLER OPEN FOR INSPECTION,



48 EXPLOSION-PROOF COAL-CUTTING EQUIPMENT.

select, there would seem to be no reason why the operator who wants
to safeguard his men can not find a unit that meets his requirements.

The cooperative spirit shown by the various manufacturers whose
machines are herein described has been greatly appreciated, and the
continuation of such relations between the bureau and those who sub-
init explosion-proof apparatus can but tend to render coal mining
safer.

Because both the “ open” and permissible or explosion-proof types
of coal-cutting machines are on the market the distinction between
them may not always be evident from the designation given them by
the manufacturer. Permissible equipments, however, can always be
distinguished by the Department of the Interior, Bureau of Mines,
approval plate, which the manufacturer is required to attach to each
approved outfit.


6 EXPLOSION-PROOF COAL-CUTTING EQUIPMENT.

Although none of the motors tested met all the conditions for
safety, the investigation was of value in laying the foundation for
future tests and development. Based on the experience gained a
schedule of tests was published by the bureau that stated the fees
and requirements for the test of motors designed for use in gaseous
mines and also stated that the bureau would give its seal of approval
to such motors as met the requirements.

The first part of the present bulletin deals with the general theory
of protection from fire damp, gives the bureau's schedule, and shows
its application to the testing of commercial apparatus. The second
part covers a detailed description of the apparatus that has been
tested and approved under this schedule, together with a résumé of
the tests on which the approvals were based.

ACKNOWLEDGMENTS.

Acknowledgment is made of the helpful cooperation that has been
given by the manufacturers of the various equipments investigated.
Acknowledgment of the gift of a new testing gallery is made to the
following manufacturers of mining equipment: Jeffrey Manufactur-
ing Co., Columbus, Ohio; Goodman Manufacturing Co., Chicago,
Ill.; Morgan-Gardner Electric Co., Chicago, Ill.; Sullivan Machin-
ery Co., Claremont, N. TI.; and Westinghouse Electric & Manufac-
turing Co., East Pittsburgh, Pa. This gallery (see detailed deserip-
tion undex Testing Equipment, p. 21) was built and installed by the
Jeffrey Manufacturing Co. The storage battery used in connection
with the outfit was donated by the Edison Storage Battery Co., of
Orange, N. J.

The investigation herein reported was begun under the direction
of H. HF. Clark, assisted by R. W. Crocker and O, I. Gaines, and was
continued by the authors.

THEORY OF FIRE DAMP PROTECTION.
OCCURRENCE OF METHANE.‘

Ordinarily, the only gas that occurs in coal nines in sufficient quan-
tities to cause an explosion is methane, CII, This gas is so preva-
Jent throughout the coal-mining regions of the United States that
mechanical ventilation is generally necessary to prevent the accumu-
lation of dangerous percentages of methane in the mine air. Effort.
is made to dilute the mine atmosphere with fresh air so that the
methane content docs not exceed one-half of 1 per cent in return air
currents. Frequently, because of improper systems of ventilation or
accidental interruption of proper systems, or becanse of the release

Darton
Mines, 1915,

N., Oveurrence of explosive
. 248.

ip coal pines, Lull, 12, Bureun of



20 EXPLOSION-PROOF COAL-CUTTING EQUIPMENT.

ITEM 2, EXTRA TESTS INVOLVING NO PREPARATION,

It is estimated that 50 tests should be sufficient to determine the permis-
sibility of the average motor or equipment offered, but the design may
be such as to require more than this number of tests to determine the
point at issue. Tor additional tests that involve no special preparation
(for each 5 tests or fraction thereof) -—--.

ITEM 8, SPECIAL ‘TESTS INVOLVING PREPARATION OF EQUIPMENT.

ecial tests involving preparation of equipment during the course of the in-
ion will be made at the request of the manufacturer and will be charged
cordance with the work involved. A deposit of $100 will be required
to cover special tests, but the entire amount will be refunded if no special
tests are made,

ITEM 4. TESTS OF STORAGE-BATTERY LOCOMOTIVES.

‘The expense of testing storage-battery locomotives in the present state of
the art can not be determined exactly and such tests will be charged for in
accordance with the work involved. A deposit of $200 will be required for
such locomotive tests. If the expense of testing is less than $200, the balance
will be refunded,

The fees specified above may be increased to cover the cost of testing an
unusually complicated type of equipment, and are also subject to change on
the recofmendation of the Director of the Bureau of Mines and the approval
of the Secretary of the Inte

SYNOPSIS OF PROCEDURE TO BE FOLLOWED IN MAKING APPLICATTO:
TESTS, SUBMITTING MATERIAL, CONDUCTING TESTS, AND NOTIFYIN
PLICANT OF RESULTS.

FOR
AP-

1. Application for tests should be addressed to the Director of the Bureau
of Mines, Washington, D. C. This application should be accompanied by check
or draft made payable to the Secretary of the Interior, and by a complete rat-
ing of the motors to be tested, and a set of the drawings described under the
foregoing heading, “Drawings of Approved Motors to be Filed.” Duplicate
copies of the application and drawings should be sent tu the electrical eugineer,
Bureau of Mines, Pittsburgh, Pa.

2, As soon as the application hay been reviewed by the bureau's engineers
the applicant will be notified of the date of tests.

3. After the applicant has received this notitication, ho should send the ma-
terial required to the electrical engineer, Bureau of Mines, Pittsburgh, Pa. The
material should be delivered not less (han one week in advance of the date set
for the beginning of the tests.

4, The tests will be begun on the date set and coutinued vutil the motor has
been approved, rejected, or withdrawn,

5, After the bureau's engineers have considered the results of the tes!
formal report of the approval or disapproval of the motor will be made to the
applicant in writing by the Director of the Bureau of Mines. No verbal re-
port will be maue, and the details of the tests must be regarded as confidential
by all present,

Vas. 1. Mayntno,
Director.
Approved Noy. 2, 1915.
Bo Swer
Assistant Secretary.



BUREAU OF MINES BULLETIN 78 PLATE XVI

A. SULLIVAN CE-7 ALTERNATING-CURRENT MACHINE.

B, SULLIVAN CE-7 ALTERNATING-CURRENT MACHINE, FRONT HEAD WITH BOTH
PROTECTIVE ELEMENTS REMOVED.



46 EXPLOSION-PROOF COAL-CUTTING EQUIPMENT.

EXPLOSION PRESSURES OBTAINED.

With the machine in the form first submitted the maximum indi-
cated pressures for the different compartments were as follows:

Mazimum pressures in machine as submitted.

In the motor compartment__-
In the controller compartment
In the fuse compartment _
In the cable-reel slip-ring compartmen

45.0 pounds per square inch.
104.8 pounds per square inch.
51.4 pounds per square inch.
48.3 pounds per square inch,

With the machine in its final form the maximum indicated
pressures were:

Maximum pressures in machine in final form.

In the nfotor compartment__
In the controller compartment. 46.5 pounds per square inch.
In the fuse compartment. 30.3 pounds per square inch.
In the cable-reel slip-ring compartment___48.3 pounds per square inch,

18.0 pounds per square Inch,

CHANGES IN DESIGN.

The chief modifications made as a result of the inspection and
tests were:

1. Fuses in the machine were made interlocking with a 3-pole
switch that must be opened in order that a fuse can be either re-
placed or taken out.

2, Unbottomed holes were eliminated in explosion-proof casings.

3. The fuse and the controller compartments were isolated from
each other and from the motor compartment.

Practical field experience with the CE-7 d. c. equipments, approvals
No. 100 and 100A, brought about the following changes in the design
of the a. ¢. machine:

1. Bell-mouthed bushings replaced cable armors of flexible tubing.

2. The discharge ports from protective devices were placed at
the sides of the machine instead of at the top.

3. The explosion-proof disconnecting plugs developed for the d. c.
cable reel were used on the a. c. cable reel.

INVESTIGATION OF THE 220-VOLT EQUIPMENT,

From a study of the drawings submitted covering the construc-
tion of the 220-volt and the 440-volt outfits the inspections and tests
of the 440-volt equipment was considered applicable to the 220-volt
equipment also, and the latter was not tested. All changes made as
a result of the inspection and test of the 440-volt equipment have
been incorporated in the 220-volt equipment. In the main, the ap-
proval of the 220-volt unit was based upon the investigation of the
440-volt outfit.


BUREAU OF MINES BULLETIN 78 PLATE VIL

A, GOODMAN 23-C DIRECT-CURRENT MACHINE.

B, GOODMAN 23-C DIRECT-CURRENT CABLE REEL AND TRUCK.


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BUREAU OF MINES BULLETIN 78 PLATE XIV

A, JEFFREY 35B DIRECT-CURRENT MACHINE.

B. JEFFREY 358 DIRECT-CURRENT MACHINE, RHEOSTAT COMPARTMENT OPEN
FOR INSPECTION.


26 EXPLOSION-PROOF COAL-CUTTING EQUIPMENT.

were promptly taken under consideration and acted on by manufac-
turers. Such a spirit of cooperation between the bureau and the
manufacturer to make approval apparatus safer can not but favor-
ably impress the mine operator and the miner.

Not only is the manufacturer expected to do his part, but the
purchaser of approved equipment should have an equal interest in its
proper maintenance. Both the user and the manufacturer have
claimed occasionally that such apparatus would not be kept clean or
would not be properly assembled after inspection. Such statements
show a wrong attitude toward safety equipment. The miners’ safety
lamp is cleaned and carefully assembled by a trusted employee. The
safety catches on a shaft cage are kept in working order. If this is
true, then the employee who has the maintenance of approved coal-
cutting equipment could be so trained that he will see in it a safety
apparatus, one in which to take pride, to inspect, to assemble
properly, and to keep at all times in a safe condition. The operator
should share with the bureau and the manufacturer the responsi-
bility for continuing the safety of approved equipment.

EQUIPMENTS APPROVED AND DESCRIPTION OF TESTS.

APPROVALS GRANTED UNDER SCHEDULES 2 AND 2A.

The coal-cutting equipments and accessories which have been tested
and approved under schedules 2 and 2A are as follows:

APPROVED EQUIMENTS.

Approval No. 100, Sullivan’ CE-7 d. ¢, machine with 250-volt motor.
Approval No. 100A, Sullivan CE-7 d. ¢, machine with 500-volt motor.
Approval No, 101, Goodman 23-€ d. c. machine with 210-volt motor,
Approval No. 101A, Goodman 28-C 4. ¢, machine with 500-voit motor.
Approval No, 102, Jeffrey 28A d. ¢. machine with 250-volt motor.
Approval No. 102A, Jeffrey 28A 4. ¢ machine with 500-volt motor.
Approyal No, 108, Jeffrey 35B d. e. machine with 250-volt motor.
Approval No, 108A, Jeffrey 35B d. ¢, machine with 500-volt motor.
Approval No. 104, Sullivan CE-7 a. ¢, machine with 220-volt motor.
Approval No, 1044, Sullivan CE-7 a. ¢, machine with 440-volt motor,

TEST PROCEDURE.

All apparatus submitted for approval under schedule 2A is first
given a preliminary inspection to detect faults of design or construc-
tion not consistent with the schedule of requirements. After this
the apparatus is tested in gas for safety from ignition of fire damp.
The cycle of operation made for a given test is as follows:

1. The equipment is placed in the testing gallery and is piped to
the gas-circulating system so that any or all compartments can be |
filled with a mixture of gas and air.


42 EXPLOSION-PROOF COAL-CUTTING EQUIPMENT.

mendations as to modifications in design, however. were withheld
until the tests were completed.

NATURE OF TESTS.

The machine with its motor, resistance and controller compart-
ments was tested in 8.6 per cent of gas. The effect of closing off and
of opening passages between compartments was studied.

The tests of the cable reel are reported under the investigation of
the 28A machine.

EXPLOSION PRESSURES OBTAINED.

The totally inclosed machine in the form first submitted gave the
following maximum, indicated pressures:

Maximum pressures in machine as submitted.

In the motor compartment ____.
In the controller compartment_.
In the resistance compartment.

- 60.0 pounds per square inch,
_ over 100.0 pounds per square inch.
~- No pressures taken.

The maximum indicated pressures for the form finally approved
were as follows:

Maximum pressures in machine as approved.

In the motor compartment. _. 62.5 pounds per square iztch.
In the controller compartment 5.4 pounds per square inch,
In the resistance compartment .4 pounds per square ineh,

In the fuse compartment........-..---- 19.8 pounds per square inch.

@

CHANGES IN DESIGN.

The changes in design found necessary from inspections and tests
are as follows:

1. Flanges were widened.

2, The resistance compartment was completely isolated from the
motor compartment, and the leads run through specially constructed
stuffing boxes packed with asbestos rope.

3. The opening between the motor and the controller compartments
was increased.

INVESTIGATION OF 500-VOLT EQUIPMENT.

From a careful study of drawings the 500-volt equipment was
seen to be mechanically the same as the lower voltage equipment and
because of this similarity one set of inspections and tests was consid-
ered sufficient for both voltages.

The 500-volt equipment has incorporated in it all the mod
that were made in the 250-volt equipment in the course of the inves-



RESUME. 47

SUMMARY,

Approvals No. 104 and No. 104A were issued January 16, 1919.
When constructed in conformity with the machine tested and ap-
proved, the CE-7, a. c. equipments are considered safe units and
are recommended for use in gaseous mines.

RESUME.

In being accorded a place in the bureau’s permissible list, the fore-
going equipments all met the requirements of Schedule 2A:

1. In construction, they are considered rugged enough to stand
reasonably severe service. The casings have adequate strength to
withstand any internal explosion of fire damp.

2. In those machines having protective devices, these devices have
proven under test to be capable of preventing the passage of flames
from the interior to the exterior of casings. The design of these de-
vices and their location within the casings afford protection against
mechanical injury while in place, and minimize the accumulation of
coal dust in openings.

3. Where flanged joints are used in explosion-proof casings these
joints have been made wide enough to satisfy the test requirements
with respect to the maximum indicated pressures during the ex-
plosion tests.

4. The construction of the machines was shown by test to prevent
the development of dangerous afterburning.

The bureau recommends al] approved equipments for use in mines
where fire damp may accumulate.

The demand for such apparatus will depend mainly on the atti-
tude that the mine owner or person in position to purchase mine
equipment has toward safety apparatus. The more the doctrine of
“safety first ” is practised the greater will be the demand for reason-
ably safe equipment.

Also, as the operator or responsible official comes more and more
to recognize the need of such apparatus and to see in it a safety
device he wil] fee] a greater interest in it and will assist the bureau
and the manufacturer in keeping it in a safe condition.

During the war there was a tendency, under the stress of the
demand for more and still more coal, to disregard safety and the de-
mand for unapproved apparatus was noticeable. When conditions
again become normal the bureau looks forward to new and greater
interest in safety methods and in safety apparatus.

The bureau has other applications on file and expects that several
more coal-cutting equipments will be added to the present list. within
the next two years. With the list already approved from which to

187337°—20-—_4


2 CONTENTS.

Schedules issued for testing explosion-proof equipment—Continued.
Procedure for establishing a list, ete.—Continued.
Fees for testing explosion-proof motors, coal-cutting equip-
ments, and locomotives.
Complete tests-.
Extra tests involving no preparation.
Special tests involving preparation of equipment.
Tests of storage-battery locomotives.
Synopsis of procedure to be followed in making | ‘applic ation for
submitting material, conducting tests, and notifying ap-
plicant of results.
Gas and equipment used.

Fan and circulating
Switchboard

Crane_.
Application of Schedule 2A to the testing of commercial equipment_
Assistance rendered by the manufacturer______-
Factors causing delay.
Drawings_.
Inspection and maintenance of approved equipment.
Equipments approved and description of tests__
Approvals granted under Schedules 2 and 2
Approved equipments

Test procedure —
Sullivan direct-current ¢
and 100A. _
Description of CH-7 direct-current equipments

Motor.

Controller and starting rheostat.

Cable reel__—.

Safety features_
Investigation of 250-volt equipment.
Preliminary inspection and recommendations.

Nature of tests.

Explosion pressures obtained.

Changes in design.
Investigation of the 500- olt equipment.
Summary -..
Goodman direct-current coal-cutting equipmen
and 1014.
Description of 28-C direct-eurrent equipment

-cutting equipments, approvals Nos. 100

Controller and starting rheostat.
Cable reel and truek with fas
and switch.
Safety
Investigation of 210-volt equipmen
Preliminary inspection and recommendations
Nature of te
Explosion pressures ob
Changes in design...

Page.

19
19
20
20
20

n
8

RRR

wy
Sea

29
29

35


BUREAU OF MINES BULLETIN 78 PLATE X

A, JEFFREY 28A DIRECT-CURRENT MACHINE.

B, JEFFREY CABLE REEL AND SWITCH FOR 28A AND 358 DIRECT-CURRENT
MACHINES.


EQUIPMENTS APPROVED AND DESCRIPTION OF TESTS. 35

tected. The trailing cables are protected at the entrances to the ma-
chines and cable reels by bell-mouthed bushings and insulated strain
clam)

INVESTIGATION OF 210-VOLT EQUIPMENT.

A 210-volt equipment comprising a motor, controller, rheostat,
and a cable reel mounted on its truck was submitted for the investi-
gation,

PRELIMINARY INSPECTION AND RECOMMENDATIONS.

The following recommendations were made after the preliminary
inspection: That the fuse box or the motor frame and the flexible
metallic tubing on the trailing cables be eliminated; that the protec-
tive devices be shrouded, and that greater care be taken to insure
no unbottomed holes in explosion-proof casings.

NATURE OV TESTS.

The tests of this machine were made with the moter running, and
7 and 8.6 per cent of gas were used both with and without coal dust.
The switch compartment of the cable reel was subjected to the same
tests as the compartments of the machine.

A special series of tests was made to determine the effect of stop-
ping off the exhaust ports of the protective devices and also the effect
of raising the cover of the commutator pit slightly.

The cable-reel switch was opened and closed under full-load cur-
rent to determine whether flashing over or dangerous burning of the
contacts would occur.

EXPLOSION PRESSURES OBTAINED.

The maximum indicated pressures for the machine as first sub-
mitted were as follows:

Maximum pressures for machine as submitted.

In the motor compartment_.
In the controller compartment.
In the resistance compartment__
In the cable-reel switch compartment_

_. 86.8 pounds per square inch.
_. 87.5 pounds per square inch,
‘Tests not made.

5.0 pounds per square inch.

The pressures ran about
closed.

After the machine was altered to conform to the final designs the
maximum indicated pressures were:

per cent higher with the exhaust ports

Mavimum. pressures after changes.

In the motor compartment__ _. 76,7 pounds per square inch.
In the controller compartment. 75.0 pounds per square inch.
In the resistance compartment___ .;-- 108.3 pounds per square inch.



50 EXPLOSION-PROOF COAL-CUTTING EQUIPMENT,

Buiter 68. Electric switches for use in gaseous mines, by H. H. Clark and
R. W. Crocker, 1913. 40 pp. 6 pls.

Briaerin 74, Gasoline mine locomotives in relation to safety and health, by
0. P, Hood and R, H, Kudlich, with a chapter on methods of analyzing exhaust
gases, by G. A. Burrell, 1915, 84 pp., 3 pls., 27 figs.

Betterix 90. Abstracts of current decisions on mines and mining, December,
1913. to September, 1914, by J. W, Thompson, 1915. 176 pp.

Buvrermy 93. Miners’ nystagmus, by F. L, Hoffman. 1916. 67 pp.

Buu.ermy 99. Mine-ventilation stoppings, with especial reference to coal
mines in Hlinois, by R. Y. Williams. 1915. 30 pp., 4 pls., 4 figs.

Buiierry 101, Abstracts of current decisions on mines and mining, October,
1914, to April, 1915, by J. W. Thompson, 1915, 138 pp.

Buuerin 102. The inflammability of Ulinois coal dusts, by J. K. Clement
and L, A. Scholl, jr, 1916. 74 pp., 5 pls, 22 figs.

Butierin 105, Black damp in mines, by G. A. Burrell, I. W. Robertson, and
G. G. Oberfell, 1916. 92 pp.

Buiern 118. Abstracts of current decisions on mines and mining, October
to December, 1915, by J. W. Thompson, 1916. 74 pp.

Bur.erin 126, Abstracts of current decisions on mines and mining, January
to April, 1916, by J. W. Thompson, 1916. 90 pp.

Buierin 131, Approved electric lamps for miners, by H. TH. Clark. 1917.
59 pp., 17 pls. 7 figs.

Buiierin 137, The use of permissible explosives in the coal mines of Mli-
nois, by J. R. Flemming and J. W. Koster. 1917. 110 pp., 8 pls., 17 figs.

TecHNIcaT PapER 2. ‘The escape of gas from coal, by H. C. Porter and ¥. K.
Ovitz. 1911. 14 pp. 1 fig.

Tecuntcas, Paver 11, The use of mice and birds for detecting carbon mon-
oxide after mine fires and explosions, by G. A. Burrell. 1912. 15 pp.

Trecnnicav Paver 17. The effect of stemming on the efficiency of explosives,
by W. ©, Snelling and Clarence Hall. 1912. 20 pp., 11 figs. 5 cents.

"rR pen 19. The factor of safety in mine electric installations, by
HT. Clark, 1912. 14 pp.

Trerica. Parer 21, The prevention of miue explosions, report and recom-
mendations, by Victor Watteyne, Carl Meissner, and Arthur Desborough. 1912.
42 pp.

Tecrrnicat Paper 23. Ignition of mine gas by miniature electric lamps with
sten filaments, by H. H. Clark. 1912. 5 pp.

‘Tecrntcat Varre 28. Ignition of mine gas by standard incandescent lamps,
by H. Td. Clark. 1912, 6 pp.

‘TecHNIcAL Laver 43. The effect of inert gases on inflammable gaseous mix-
tures, by J. K. Clement, 1918. 24 pp., J pl. 8 figs.

Tecnnical. Paver 44. Safety electric switches for mines, by H, H. Clark.
1913, 8 pp.

TeckNicat Papre 62. Relative effects of carbon monoxide on smal avimals,
by G. A. Burrell, F. M. Seibert, and J. W. Robertson. 1914. 23 pp.

‘Tecuuicat Papre 75. Permissible electric lamps for miners, by H. H. Clark.
1914. 21 pp. 8 figs.

TecHNicaL Parex $2, Oxygeu mine rescue apparatus and physiological effects
on users, by Yandell Henderson and J. W. Paul. 1917. 102 pp. 5 pls, 6 figs.

Tecuxicar Parse 84, Methods of preventing and limiting explosions in coal
mines, by G. 8. Rice and 1. M, Jones. 1015. 50 pp., J4 pls, 5 figs.

‘Teernican Paree 100. Permissible explosives tested prior to March 1, 1915,
by 8. P. Howell, 1915. 16 pp.

to



THEORY OF FIRE DAMP PROTECTION. 13

In this type of protective device so many layers of gauze are neces-
sary to insure good protection that the ventilation of the apparatus
is greatly reduced and the pressure developed approaches the condi-
tion of a totally inclosed equipment. Protective devices of the wire
gauze type should be well shrouded to keep out dust.

PLATE PROTECTION.

As has already been stated wide flanges abstract heat from flames
passing through flanged joints. Plate protection does the same on a
larger scale. A large number of thin plates are separated by other
plates or spacers, and are rigidly riveted or bolted together. They
require more space than heat abstractors of the gauze type, but they
permit better ventilation. Because this type has comparatively large
openings through which the pressure is relieved, the internal explo-
sion pressure developed is correspondingly lower. This type should
also be well shrouded in order to keep out dust.

GENERAL REQUIRE

The preceding types were used in the apparatus submitted for ap-
proval, however, other designs also have been used. The aim in all
designs is to bring the hot flames in contact with as large an area of
metal as possible.

Protective devices in order to be practical must have mechanical
strength, durability, uniformity, and simplicity of parts, and protec-
tion from dust and inechanical injuz

Mechanical strength is needed to insure a permanent and definite
relation of parts in spite of severe mine service or strains resulting
from internal explosions.

The elements making up the device should be durable and not
affected by heat or moisture.

A certain simplicity and uniformity of construction should be used
in order that the devices shall haye an identical assembly for all
equipments, and that mistakes shall not be made in assembling or in
reassembling after inspection. The flame safety lamp is a good ex-
ample of this for, although not “fool proof,” it is so constructed that
a mistake in assembly is inexcusable.

Such devices should always be protected from the accumulation of
coal dust by making the ports on the side or bottom of the apparatus
instead of on the top, aad the interior construction, as far as possible,
should be designed to prevent the collection of coal dust. The pro-
tective devices should also be well protected from mechanical injury,



EQUIPMENTS APPROVED AND DESCRIPTION OF TESTS. 41

theostats for both voltages. The cover a of the resistance compart-
ment is removed to show the 250-volt rheostat & in position. The
theostat ¢ at the right replaces the 250-volt rheostat when the ma-
chine is built for 500-volt service. The casting d protects the insu-
lated studs e, by which power is supplied to the machine through
the resistance compartment. The insulated clamp f relieves the
studs of strain. A bell-mouthed bushing forms a part of the
casting d.
CABLE REEL AND TRUCK WITH FUSE AND SWITCH,

These parts have already been described for the 28A machine and
are shown in Plates X, B, and XIII, A and B.

SAFETY FEATURES.

The 35B machine uses the totally inclosed form of construction
with broad flanges. The flange joints are held together securely with
ample bolts and studs, which have bottomed holes. The flanges and
casings are properly proportioned for the maximum internal explo-
sion pressures that may develop.

The wiring between the motor, the controller, and the rheostat is
inclosed in the casings and is well protected from mechanical injury.
Where the cable enters the machine a bell-mouthed bushing mini-
mizes abrasion. The wiring between the cable reel and the fuse box
is run in flexible, metallic tubing for protection.

The terminal plugs on the machine cable are interlocked with the
switch in the explosion-proof compartment in order to prevent arcs
and flashes from being drawn into the atmosphere when the plugs
are removed. The switch must first be opened and the cover of the
compartment moved to the right before the plugs can be withdrawn.
The switch can not be closed unless the cover is in its proper position.

INVESTIGATION OF 250-VOLT EQUIPMENT.

The Jeffrey Manufacturing Co. originally submitted its 85B ma-
chine with the plate type of protective devices. An investigation,
including inspection and several series of tests, had been made of the
machine in this form, when its return to the factory for modification
became necessary.

While at the factory the use of protective devices was abandoned,
and the machine was rebuilt in the totally inclosed form and resub-
mitted for test and approval. One cable-reel truck with reel, fuse,
and switch was submitted for the investigation of both the 28A and
35B equipments.

PRELIMINARY INSPECTION AND BECOMMENDATIONS.

The initial inspection of the totally inclosed form of 38B ma-
chine showed several unsatisfactory details of construction. Recom-


BUREAU OF MINES BULLETIN 78 PLATE XVIII

A. SULLIVAN CE-7 ALTERNATING-CURRENT CABLE REEL.

B, SULLIVAN CE-7 ALTERNATING-CURRENT CABLE REEL DISMANTLED TO SHOW
INTERIOR OF SLIP-RING COMPARTMENT AND DETAILS OF DISCONNECTING
PLUG.


SCHEDULES ISSUED FOR TESTING EXPLOSION-PROOF EQUIPMENT. 15

1. The tests will be made at the experiment station of the Bureau of Mines
at Pittsburgh, Pa.

2. Applications for tests shall be addressed to the Director, Bureau of Mines,
Washington, D. ©., and shall be accompanied by a certified check or draft
made payable to the Secretary of the Interior to cover the fees, and by the
information specified below :

(a) The complete rating of the motor in accordance with the 1914 stand-
ardization rules of the American Institute of Electrical Engineers.

(4) Dimension drawings that show clearly—

The size and general appearance of the motor casing.

The size and details of the protective devices and their relative arrange-
nent on the motor casing.

The relative arrangement of the parts within the motor casing.

The same information in regard to the starting rhcostat and controlling
appliances as is requesed for the motor.

y other drawings necessary to identify or explain any feature that Is to
be considered in the approval of the motor or its accessories,

A copy of the description and a duplicate set of the drawings shall be sent
to the clectrical engineer, Bureau of Mines, Pittsburgh, P

3. As s ble after the receipt of application for test the manu-
facturer will be notified of the date on which his motor will be tested.

4, The manufacturer is to deliver to the Bureau of Mines, Pittsburgh, Pa.,

one week prior to the date set for the test, the motor that he desires tested,
completely prepared for test in every particular. If requested to do so, the
manufacturer shall provide a man to assist in mounting the moter and connect-
ing it for test; and the manufacturer, if he so desires, may have a representative
present throughout all the tests.
. No one is to be present at the time these tests are made except the
necessary Government officers at the experiment station, their istants, the
representative of the manufacturer of the motor under test, and such other
persons as may be mutually agreed upon by the manufacturer and the repre-
sentatives of the bureau.

6. No tests leading to an approval will be made of any motor unless
in the completed form in which it is to be put on the market,

7. The tests will be made in the order of the receipt of application for them,
provided that the necessary equipment is submitted at the proper time.

8. The details of the results of the tests shall be regarded as contidential by
all present at the tests and shall not be made public in any way prior to the
formal approval of the motor by the Bureau of Mines.

it is

REQUIREMEN’

FOR APPROVAL OF MOTORS,

The qualifications that an explosion-proof equipment must have to pass suc-
cessfully the inspection and tests required by the bureau are stuted below:

CONSTRUCLION.

‘The construction of permissible explosion-proof motors and their accessories
must be especially durable, ‘This requirement will be applied consistently to
all the details of the machine, as well as to its principal parts, in order that
there may be assurance that, under the severe conditions imposed by mining
service, the explosion-proof qualities of the equipment wil! remain unimpaired.

The protective devices used with permissible explosion-proof motors must not
only be capable of preventing the passage of flames from the interior to ihe

137337°—20 2



CONTENTS.

Introduction ~
Acknowledgments —.
Theory of fire damp protection.
Oceurrence of methane.
Explosive limits of fire damp.
gnition temperature of methane.
Presence of fire damp in electrical apparatus.
Conditions necessary for explosion.
Factors bearing on safety...

Spread of explosions through openings in apparatu:
Effect of internal spacing on internal pressure
Explosion pressures of mixtures of gus and air
Effect of coal dust in the apparatus_.
Construction of equipinent-.
Gas-tight apparatu:
Yotally inclosed apparatus
Partly inclosed apparatu
General rules for construction.
Construction of protective devic
Wire gauze protection_
Plate protection
General requirements.
Schedules issued for testing explosiou-proof equipment.
Procedure for establishing a list of permissible explosiou-proot elec-
tric motors...
General statement. -
Definition of “explosion proof
Definition of “ permissible”.
Conditions under which motors will be tested.
Requirements for approval of motors.
Construction 22 2
Gontrolling applinnces
Motor casing.
Cable reel and trailing cable.
Character of tests to which motors will be sub
Caution and approval plates.
Notification of manufacture
Drawings of approved motors to be fled
Scope of approval... ...-.----
Withdrawal of approval. —....
Tests of storage-battery locomoti

19


32 EXPLOSION-PROOF COAL-CUTTING EQUIPMENT.

1. A bell-mouthed bushing replaced the flexible metallic tubing
submitted for the protection of the trailing cable from abrasion
where it entered the machine and the cable reel.

2. The openings at the top of the machine for the discharge from
the protective devices became packed with dust. The manufacturer
yedesigned the machine so that the discharge was downward and at
the side of the machine, thereby overcoming this defect.

8. The cable-reel disconnecting plugs were found to be inadequate
in service, and after successive trials a design was evolved that
proved satisfactory under severe tests.

The above changes were recommended by the bureau and were
promptly made by the Sullivan Machinery Co. The approvals of
the d. c. machines were extended to cover these different modifica-
tions. Plates III, A and B, IV, V, A and B, and VI, A and B, show
assembled and detailed views of the latest design of equipments in
which are incorporated all of the improvements just mentioned.

INVESTIGATION OF THE 500-VOLT EQUIPMENT,

From a careful study of the machine construction it was deter-
mined that a repetition of tests already made with the motor, con-
troller, and rheostat of the 250-volt equipment was unnecessary with
the same parts of a 500-volt equipment. Separate tests, however,
were made of the cable-reel disconnecting plugs and fuses designed
for 500-volt service.

In the main the approval of the 500-volt unit was based upon the
tests of the 250-volt equipment. All improvements and modifica-
tions made as the result of the laboratory and ficld investigations of
the 250-volt equipment have been incorporated in the 500-volt
machine.

SUMMARY.

Approval No. 100, granted September 30, 1914, and approval No.
100A, granted October 20, 1914, were extended to eover changes in
the cable entrance to the machine and a modification of protective
devices on October 5, 1915, and to cover improvements in the cable-
reel disconnecting plugs on March 10, 1916. When constructed in
conformity with the machine tested and approved, the CE-7 d, c.
equipments are considered safe units and are recommended for use in
gaseous mines.

GOODMAN DIRECT-CURRENT COAL-CUTTING EQUIPMENTS, AP-
PROVALS NO. 101 AND 1014.

The Goodman Manufacturing Co.. of Chicago, TL, made appli-
cation under Schedule 2 for the lest and approval of a 210-volt
equipment and submitted a 210-volt outfit for inspection an‘ test.


24 EXPLOSION-PROOF COAL-CUTTING EQUIPMENT.

CRANE,

Plate I, A, shows the gallery superstructure and the hoist used in
connection with the testing gallery. The 3-ton hoist ¢ raises and
lowers the cover, or transfers apparatus in or out of the chamber,
and when necessary lifts the cylinder from the concrete base. The
ropes ¢ are attached to the hoist and are used to pull it in either
direction along the I-beam d.

After cach test the cover is raised to air out the chamber and to
permit the operator to enter it. As the entire top of the chamber
can be lifted, the gas can be removed quickly and there is little delay
between tests.

APPLICATION OF SCHEDULE 2A T0 THE TESTING OF COMMERCIAL
EQUIPMENT.

ASSISTANCE RENDERED BY THE MANUFACTURER.

The manufacturer who submits equipment for test is required to
furnish one man familiar with the equipment to assist with the in-
vestigation. This man may or may not represent the manufacturer
as a witness at the tests. His chief service to the bureau is to assist
in setting up the equipment for test and in making any changes
necessary in the progress of the investigation. The manufacturer
is expected to prepare the equipment for test in so far as concerns
drilling holes and tapping holes for the circulating pipes, pressure
gage, and spark-plug connections. This work is laid out by the
bureau’s engineers and then done either at the bureau’s machine
shop or at some nearby plant by the company submitting the ap-
paratus.

FACTORS CAUSING DELAY.

In the bureau’s tests of commercial equipment there are several
causes of delay that have considerably increased the expense to the
several submitters. By noting the following deficiencies future ap-
plicants may avoid similar troubles. Almost all equipments sub-
mitted have had holes through the casing walls instead of bottomed
holes or some other means of preventing an accidental opening by
the omission of a bolt, although this is contrary to the schedule re-
quirement. In many equipments the flange making up the flange
joint is not effective either because of higher internal pressures
than were expected or of insufficient contact of the metal at certain
points where the castings do not align properly or where material
is insufficient. Excessive pressure in the final compartment of the
series, caused by the propagation of explosions from one compart-
ment to another, has made changes in design necessary and has
seriously delayed the tests.



The Bureau of Mines, in carrying out one of the provisions of Its organic
act—to dissenfinate information concerning investigations made—prints a
limited free edition of each of its publications,

When this edition is exhausted, copies may be obtained at cost price only
through the Superintendent of Documents, Government Printing Office, Wash-
ington, D. ©.

‘The Superintendent of Documents is not an official of the Bureau of Mines,
His is an entirely separate office and he should be addressed :

rrment Printing Office,
Washington, D. C.

The general law under which publications are distributed prohibits the giv-
ing of more than one copy of a publication to one perse’ The price of this
publi cents.

Persons desiring for lecture purposes the use, free of charge, of lantern slides
of the illustrations in this publication. should make request to the Director of
the Bureau of Mines, Washington, D. C.

First cdition. February, 1920,


38 EXPLOSION-PROOF COAL-CUTTING EQUIPMENT.

blade @ is operated by the handle 8, The fuse is further inclosed
within a rectangular chamber, g, built up of noncombustible material.
The machine may be entirely disconnected from the circuit by pull-
ing the cable terminal plugs, ¢, from the openings, @, but only after
the switch has been opened and the flanged cover, ¢, has been let
down. The wiring between the cable reel and the fuse and switch
compartment is carried in flexible, metallic tubing, 7.

In Plate XIII, B, the fuse and switch compartment is closed and
the separate compartment containing terminal connections is open.

SAFETY FEATURES.

All compartments, including the fuse and switch compartment, are
totally inclosed and depend on broad flanges for explosion-proof pro-
tection. The flanges have been designed to withstand the maximum
internal explosion pressure developed and are well secured with ample
studs and bolts that have bottomed holes.

The wiring between the motor, the controller, and the rheostat is
within the machine and is therefore well protected from mechanical
injury. The cable is protected by a bell-mouthed bushing where it
enters the main frame and by an insulated strain clamp where it con-
nects with the studs through the explosion-proof casing. Flexible
metallic tubing is used to protect the wiring between the cable reel
and fuse box.

The terminal plugs of the machine cable can not be withdrawn
under load and therefore can not produce dangerous arcs or flashes.
They are so interlocked with the switch that the latter must be opened
in order to release the cover, which then has to be moved to the right
before the plugs are free to be pulled out.

INVESTIGATION OF 250-VOLT EQUIPMENT.

A 250-volt equipment, which included the motor, the controller,
the rheostat, and a cable reel with fuse and switch, was submitted
for the investigation.

PRELIMINARY INSPECTION AND RECOMMENDATIONS.

The preliminary inspection disclosed certain deficiencies that
needed to be remedied, namely—

1, Several bolt holes in explosion-proof casings were not bot-
tomed.

2. An insulated cable clamp was not provided with the machine.

3. Unsuitable material was used for covers of explosion-proof
compartments.

+. Several modifications in the fuse box were necessary.

Recommendation was made that the company consider the ad-
visability of the above changes.


EXPLOSION-PROOF COAL-CUTTING EQUIPMENT.

30

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EQUIPMENTS APPROVED AND DESCRIPTION OF TESTS. 27

2, Arrangements are made for the installation of spark plugs at
different points in order that the point of ignition shall be under
the operator’s control.

3, Provision is also made to connect a pressure indicator at
different points in order to obtain a record of the pressure developed
by the explosion in the compartment under observation.

4, In tests to determine the effect of the presence of coal dust in the
atmosphere, the dust is sifted into the openings or into the compart-
ments proper.

5. When the spark plug and pressure indicator have been con-
nected at the desired points, the testing gallery is closed, and an
explosive mixture of gas and air is made by adding the proper
quantity of gas and thoroughly mixing it with the air.

6, The explosive mixture is then drawn into the compartment or
compartments under test.

7. Observers are stationed at the observation windows of the
gallery.

8. The mixture within the compartment is ignited by means of
the spark plug, and this ignition is automatically timed with the
release of the indicator drum to give a satisfactory pressure diagram.

9. Observations are recorded.

10, The gallery is opened and the gas mixture removed by the
circulating system.

11. The operator enters the gallery, makes his inspection, removes
the indicator card and prepares the motor for the next test.

The percentages of gas generally used in the tests are 8.6 and 7.0,
both with and without coal dust.

During these tests the gas mixture surrounding the apparatus
must not ignite, flames must not pass through the flange joints, bear-
ings or protective devices, and prolonged afterburning or excessive
pressure must not develop in any of the compartments.

SULLIVAN DIRECT-CURRENT COAL-CUTTING FQUIPMENTS, AP-
PROVALS NO. 100 AND 100A.

The Sullivan Machinery Co. of Claremont, N. H., made ap-
plication under Schedule 2 for the test and approval of a 250-volt
equipment and submitted a machine equipped with a 250-volt motor
for inspection and test. Later a request was made for the approval
of a 500-volt equipment. - The company was not required to submit
a complete 500-volt unit, but only 500-volt fuses and cable-reel dis-
connecting plugs, as the mechanical construction for the two voltages
was so nearly identical that the investigation of the 250-volt equip-
ment could be held to apply to the higher voltage machine in all
other respects,


THEORY OF FIRE DAMP PROTECTION. il

particles are forced out into the surrounding atmosphere, they cool
almost instantly and are above the ignition temperature of methane
for so short a time that they probably can not ignite fire damp and
thus cause an explosion.

CONSTRUCTION OF EQUIPMENT.

The chief problem confronting the manufacturer of apparatus
suited for fire damp atmospheres is that of extracting heat from
possible explosion flames and of cooling them below the ignition
temperature of methane (650° C.) as they pass through the openings.
Cooling may be the result of contact of the flames with metallic
joints or openings through which they pass or by sudden expansion
of the gases from a comparatively high pressure within to the atmos-
pheric pressure without, or by both. In fact, while one or the other
of the above conditions may predominate, some cooling and some
expansion will always take place, as the escaping flames. must come
in contact with the sides of the openings and the internal pressure
exceeds atmospheric pressure.

Apparatus of this kind can be classified as follows: Class 1, gas-
tight apparatus; class 2, totally inclosed apparati class 3, partly
inclosed apparatus,

GAS-TIGHT APPARATUS,

Class 1 includes apparatus made with absolutely gas-tight com-
partments. Such apparatus is not practical for mine service, beca
of the difliculty of inspection and of making renewals. Moreover,
the ordinary materials used in packing joints would deteriorate in a
mine, Therefore, this class of equipment has been used but little.

TOTALLY-INCLOSED APPARATUS.

Class 2 includes apparatus that has no openings, except flange
joints, the openings of which can be closed tight enough to prevent
explosions within the apparatus from spreading to the surrounding
atmosphere. Obviously, a given size of motor, when used in a
totally-inclosed machine, must be rated somewhat lower than when
used in one that is ventilated. Apparatus of this class has, however,
the advantages of simplicity of design, slight deterioration, and free-
dom from excessive dust troubles.

PARTLY-INCLOSED APPARATUS,

Class 3 includes apparatus with openings that afford a certain
amount of ventilation—openings in which are placed heat-abstract-
ing devices, in this paper called “protective devices.” The flange
joints are of the same characteristics as those of the second .class,


EQUIPMENTS APPROVED AND DESCRIPTION OF TESTS. 45

The usual precautions have been taken in supplying for all joints
between compartments, or for covers of compartments, wide flanges
secured with studs or bolts with bottomed holes.

The wiring between the motor, the controller, and the fuse com-
partments is well protected, as it is run within the machine. The
trailing cable is protected from undue abrasion where it enters the
fuse compartment and the cable-reel disconnecting plugs by bell-
mouthed bushings. Insulated clamps relieve the cable connections of
strain in the fuse compartment and in the cable-reel plugs.

INVESTIGATION OF 440-VOLT EQUIPMENT.

The equipment submitted for the investigation consisted of a
three-phase, 440-volt motor with controller, fuses, and cable reel.

The machine in its first form failed to pass the tests, and an in-
vestigation was made to determine the design best adapted to meet
the conditions of the schedule. In the redesigned form that was
approved the motor has a double-element protective device of the
plate type in both front and rear heads, and the fuse and controller
compartments are isolated from each other and from the motor com-
partment. The cable reel was also redesigned.

PRELIMINARY INSPECTION AND RECOMMENDATIONS,

The preliminary inspection of the original machine showed that
the fuses could be withdrawn under load. A recommendation was
made that the fuses be locked in some manner to prevent this.

Later in the investigation recommendations were made that the
flexible-cable armors should be discarded and bell-mouthed bushings
substituted, that the cable-ree] disconnecting plugs should be made
explosion-proof, and that the location of openings into protective
devices should be changed so as to minimize the possibilities of
dust entering the devices and machine.

NATURE OF TESTS,

The tests on the machine in the form finally submitted were made
with 7 and 8.6 percentages oi gas with and without coal dust. The
motor was running in nearly all tests. The investigation of the
magnetic blow-out type of cable-reel disconnecting plugs furnished
with the d. c, machine, approvals 100 and 100A, was held to apply
for the three-phase reel, since the plugs were identical in design and
since they were formerly tested for 500 volts, whereas only 440 volts
would be used on the a. c. reels,


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EQUIPMENTS APPROVED AND DESCRIPTION OF TESTS. 39

NATURE OF TESTS.

In the tests upon the machine proper the motor was running and
7 and 8.6 percentages of gas were used. The fuse and switch com-
partments attached to the reel truck were tested with 8.6 per cent gas.

EXPLOSION PRESSURES OBTATNED.
The maximum indicated pressures for the tests were as follows:

Maximum indicated pressures,

In the motor compartment_...
In the controller compartment .
In the resistance compartment.
In the fuse compartment__

_ 73.8 pounds per square inch.
_. 66, 6 pounds per square inch.
_ 83, 8 pounds per squire inch.
_ 19.3 pounds per square inch.

As the changes made in the design had no bearing on explosion pres-
sures developed, the original pressures stand as representative of the
equipment approved.

CHANGES IN DESIGN.

As a result of recommendations and tests made by the bureau
certain minor changes in design were made, namely—

1. Covers of explosion-proof chambers were made of cast steel in-
stead of boiler plate.

2. Castings were modified to eliminate unbottomed holes in explo-
sion-proof casings.

3. Flanges were made wider.

4, An insulated strain clamp was provided to relieve the strain on
the hand cable connecting the reel and the machine.

5. The arrangement of the insulating barriers in the fuse box was
changed to make the fuse more accessible for renewals and to inclose
the fuse completely.

INVESTIGATION OF 500-VOLT EQUIPMENT.

A careful study of the drawings submitted showed that mechani-
cally the 28A machine was the same for either voltage. A repetition
of inspection was therefore unnecessary for the higher voltage equip-
ment. The space occupied by the rheostat units was practically the
same for cither voltage, hence as regards explosion-proof protection
another set of tests was not required.

All changes in mechanical construction which were made in the
interests of safety and for improvement during the investigation of
the 250-volt machine were embodied in the 500-volt machine.

Approval No. 102A was granted principally upon the basis of the
investigation of the 250-volt equipment, which met the requirements
of the schedule.


14 EXPLOSION-PROOF COAL-CUTTING EQUIPMENT.
SCHEDULES ISSUED FOR TESTING EXPLOSION-PROOF EQUIPMENT.

Schedule 2, approved by the Secretary of the Interior, October 26,
1911, was the first schedule issued. This schedule stated fees that
would be charged and conditions and requirements under which tests
of explosion-proof motors would be made. One investigation was
completed under its regulations, Schedule 2A%, revised edition of
Schedule 2, was issued November 2, 1915. The remaining investiga-
tions reported in this bulletin were made under its regulations. The
full text of Schedule 2A follows

PROCEDURE FOR ESTABLISHING A LIST OF PERMISSIBLE EXPLO-
SION-PROOF ELECTRIC MOTORS.

GENERAL STATEMENT,

An act of Congre:
following pro

That for tests or investigations authorized by the Secretary of the Interior
under the provisions of this act, other than those performed for the Govern-
ment of the United States, or State governments within the United States, a
reasonable fee covering the necessary expenses shall be charged according to @
schedule prepared by the Director of the Bureau of Mines and approved by the
Secretary of the Interior, who shall prescribe rules and regulations under
which such tests or investigations may be made, All moneys received from such
sources shall be paid into the Treasury to the credit of miscellaneous receipts.

(87 Stat. 681) approved February 25, 1918, contains the
sion in regard to tests performed by the Bureau of Mines:

The Bureau of Mines is making tests at its Pittsburgh experiment station in
the endeavor to establish a list of permissible explosion-proof electric motors for
use in mines, This schedule is issued for the information and guidance of
those who may desire to submit equipment for test. It supersedes Schedule 2
issued under date of January 1, 1912, and goes into effect on approval by the
Secretary of the Interior.

DEFINITION OF “EXPLOSION PROO’

The Bureau of Mines has applied the term “explosion proof” to motors
constructed so as to prevent the ignition of gas surrounding the motor by any
sparks, flashes, or explosions of gas or of gas and coal dust that may occur
within the motor casing,

DEFINITION OF “ PERMISSIBLE.”

The Burenu of Mines considers any motor to be permissible when it is the
same in all respects as a sample motor that has passed certain tests made by
the bureau and when it is installed and used im accordance with the conditions
prescribed by the bureau.

CONDITIONS UNL

R WHICH MOTORS WILL BE TESTED,

The conditions under which the Bureau of Mines will examine and test
exploslon-proof motors to establish their permissibilily are as Lollows:

Procedure for sabibiishing a Ist of permbaafble explosion-proof clectrie motors for
mines, fees, nditions under which motors will be tested, Schedule
DA. Bureau of Mines, Nov. 21, 1915, 11 pp.