EPA 430/9 75 004
SCHOOL WATER SUPPLY
FLUORIDATION
ENVIRONMENTAL PROTECTION AGENCY
mmmmmamamammm
WATER SUPPLY DIVISION
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School Water Supply Fluoridation
by
Ervin Bellack
ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF WATER AND HAZARDOUS MATERIALS
WATER SUPPLY DIVISION
WASHINGTON D.C.
First printed 1972
Reprinted 1975
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School Water Supply Fluoridation
After 25 years of progress, the fluoridation of community water supplies
has become a widely accepted practice, and with the adoption of legislation
in many States, the trend is toward almost universal treatment of these supplies
with fluoride. Yet, very little progress has been made toward extending the
benefits of fluorides to the 46 million persons, about 23% of the total
population, who reside in areas not served by central water supply systems.’
A number of alternative methods for providing dental caries protection for
these people have been suggested; among them individual home fluoridators,
fluoride tablets, and the fluoridation of the water supplies of rural schools.
This latter method seems particularly appealing, since it would reach sizeable
numbers of children with minimal demands on personnel, equipment, and
funds.
There are some basic differences between municipal and school fluoridation
which prevent drawing a direct parallel between the two methods. One of the
obvious limitations imposed on school water fluoridation is that children are
5 or 6 years old before they begin attending school and consuming the water,
whereas maximum dental benefits appear to accrue when fluoridated water
is consumed from birth. 2 However, in communities that have instituted
controlled fluoridation, data have been obtained which indicated that
children who are 6 years old or older at the time fluoridation is initiated
do derive considerable benefits from the procedure The potential for
caries inhibition would be greatest in the later erupting permanent teeth, but
there is evidence that teeth already erupted derive some caries-inhibitory
benefits from the topical action of fluoridated water. 8 ’°
A second factor limiting the effectiveness of having only the school water
supply fluoridated in a community is that the exposure to fluoridated water
in a school is intermittent, since children attend school only five days a week
for only part of the day and for only part of the year. Recent studies, how-
ever, have reported that some benefits are derived from belated and inter-
mittent exposure to fluoridated water, and these findings have led to the
hypothesis that control of dental caries can be expected from the fluoridation
of school water supplies, particularly if the level of fluoride is maintained at
a concentration high enough to compensate for the late and limited exposure
factors discussed.’
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STUDIES OF EFFICACY
A pilot study testing this hypothesis was instituted in 1954 in the Virgin
Islands.’ 5 In an attempt to duplicate the total fluoride intake of children who
drank optimally fluoridated water on a full-time basis, the water supplies of
two schools were fluoridated at a level approximately three times that recom-
mended for community fluoridation in the area. A dental survey conducted
after six years of school fluoridation showed that children in one of the test
schools which had a record of fairly continous operation had about 22%
fewer cavities than did children who attended comparable schools without
fluoridation.
Two additional school fluoridation studies were begun in 1957. In Pike
County, Kentucky, the fluoride levels in two schools were maintained at 3.3
thnes the recommended optimum for community fluoridation, and in Elk
Lake, Pennsylvania, the level was maintained in another school at 4.5 times
the recommended optimum for community fluoridation. Final results from
these studies are not yet available, but interim results after eight years of
school fluoridation showed reductions in decayed teeth approaching 35%
at each of the study sites.’ 6 ’ 2 ’
SAFETY
Since the raising of the fluoride level in the school fluoridation studies
mentioned above resulted in greater decay reduction, it has been theorized
that still higher levels might impart even greater benefits. However, the ques-
tion of safety must always be considered, since it is known that full-time
exposure to fluoride levels even as low as twice the optimum can cause some
degree of dental fluorosis. Yet, fmdings of epidemiological studies have
shown that children who consume water at home that was virtually fluo-
ride-free, but who, when at school, drank water with natural fluoride levels
of 6’ and 14 ppm,’ 8 were uniformly free of any objectionable signs of
dental fluorosis. Data obtained from examinations for fluorosis on children
participating in the school fluoridation studies in Elk Lake are in keeping
with these results.’ 6 An examination of 281 children at Elk Lake, after
eight years of school fluoridation at 4.5 times the optimum level showed that
only one child was classified as having definite fluorosis, and this was of the
very mild type. 16 In fact, the effect of school fluoridation at somewhat
elevated fluoride levels may provide an improved aesthetic appearance.
SELECTING A SCHOOL
Two of the primary requirements for school fluoridation are that the
students of the school do not consume fluoridated water from any other
source and do not receive dietary fluoride supplements. The requirement
with respect to fluoridated water can usually be met when the school enroll-
ment comes from a community which does not have municipal fluoridation,
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or when the students come from homes which have individual well water
supplies. In the former case, the possibility of eventual community fluorida-
tion should be carefully considered, and if there is even the slightest possibility
of such an event, it would be more advantageous to work toward fluoridation
of the entire water supply rather than that of each individual school. In the
latter case, a representative number of the individual well supplies should be
checked to verify the lack of significant concentrations of natural fluoride.
l’his level, established solely on an empirical basis, should be no greater than
one-third the optimum for community fluoridation in the geographic area.
An individual well supply for the school is also a mandatory requirement, since
the engineering problems involved in fluoridating a single building or group of
buildings on a municipal water supply are prohibitive, and there is always
the possibility that the municipality will institute community fluoridation,
affecting not only the school, but probably the homes of the students as well.
In fluoridating a school water supply to levels greater than established
optimum levels for a community water supply, besides determining that the
students do not receive fluoride supplements and are exposed to no other
source of fluoridated water, there also exists the problem of having private
residences connected to the school water system. The latter situation may
occur in rural schools, where the principal, maintenance personnel, or
other staff and their families live in homes on the school grounds. To
avoid the full-time exposure of very young children in those families to
high levels of fluoride, provisions must be made to exclude these residences
from the fluoridated water. In most cases it will be a matter of doing a
little more plumbing to isolate a residence from the high-fluoride water.
Specifically, the take-off point for the residence water supply will have
to be relocated to a point between the well pump and the fluoride-injection
and metering point, and a backflow prevention device added to the pipe line
to prevent the fluoridated water from flowing toward the house when the pump
is idle or inoperative for some reason. Depending on individual circum-
stances, a separate hydropneumatic tank and pump controls may be required.
IMPLEMENTATION
The engineering aspects of school water fluoridations, with the exception
of maintaining a higher fluoride level, are fundamentally similar to those
of community water fluoridation. Essentially, a school water supply is the
same as that of many small communities, and usually consists of an unattended
well pump, a storage tank (either elevated or hydropneumatic) and a distribu-
lion system. The fluoridation installation consists of a solution container,
a solution feeder and, for the purpose of maintaining records, a water meter.
The fluoride feeding equipment used in the study projects has varied depend-
ing upon the size of the water system, its complexity and the conveniences to
the operator that were built into the system. The adequacy and quality of the
water supply, its pressure and storage capacity and the type and availability
of personnel to operate the system were also important determinants in select-
ing equipment.
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The earliest study projects utilized a small solenoid-operated diaphragm
feeder, and the source of fluoride ion was a solution of magnesium silico-
fluoride. This particular chemical was chosen because solutions had to be
centrally prepared, and the high solubility of magnesium silico fluoride per-
mitted preparation of stronger solutions and thus, less frequent refIlls. These
early studies were also dependent on centrally-located operators, such as
county or state public health personnel, for survefflance and maintenance.
Experience has shown that the installation should be designed to be as
simple and trouble-free as possible in order to assure uninterrupted operation,
and that a local operator, such as a high school science teacher, a principal,
or a custodian at the installation site is a better choice than a centrally-located
operator. Since schools having their own water supplies are usually rural, they
are usually located at considerable distances from a county or state health
agency capable of providing the skills necessary for surveillance and main-
tenance. Thus, when an adjustment of fluoride level is indicated or mechanical
failure occurs, there is inevitably a delay before adjustment or repairs can be
effected. If, on the other hand, the installation is operated by interested local
personnel, any delay is minimal. With adequate training, almost anyone can
perform routine fluoride analyses and maintain the equipment, provided of
course, the type of equipment is tailored to the skill and experience of the
operator. Although individual circumstances may dictate other choices, the
use of local operators has resulted in the evolution of an installation design
based on the use of a sodium fluoride saturator, a device for providing a
constant supply of fluoride solution of fixed strength with minimal operator
attention.
PROCEDURE
Although specific details regirding the equipment and facilities applicable
to all school fluoridation installations cannot be prescribed due to the widely
varying conditions existing at each prospective site, a generalized step-by-step
procedure having wide application has been derived, based on the design men-
tioned above. Before the actual installation of any fluoridating equipment can
be made, however, it must be ascertained that the school meets the previously
specified requirements, that all necessary approvals have been obtained, and
the level of fluoride to be fed has been agreed upon. (A level of four and one-
half times the optimum for community fluoridation in the geographic area
is currently recommended by the U. S. Public Health Service.)
Step I: Locate the point in the system where the water flow represents the
total output of the well or spring, and where the flow is maintained at the
operating pressure of the school water system. This point will be the site
of fluoride injection and flow metering so its selection is of primary
importance. The fluoride injection point may be adjacent to the well or
spring itself, in a crawl space under the school building, or adjacent to the
hydropneumatic tank or elevated storage tank. If one of the latter sites is
chosen for flow metering and fluoride injection, the absence of branch lines
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between the well and the pressure tank must be positively verified. If branch
lines do exist, and particularly if a line to a residence exists, the fluoride
injection and flow metering point must be located so that the former are
included in the system to be treated, while the latter is specifically excluded.
This may involve relocating a pipe line, as mentioned earlier. Under no circum-
stances should a point in the output of the water storage facility be selected as
the fluoride injection and flow metering point, for there the water flow may
vary from zero (when the storage merely “rides” on the system) to the maxi-
mum capacity of the system derived from pipe size and pressure. The simpli-
city of the installation is dependent on a flow rate which is essentially constant,
as typified by the flow between a well or spring box pump and storage facility.
Step II: When the metering point is located, determine the pump delivery
rate. This may be recorded or available from the pump manufacturer, or
can be estimated from the horsepower rating, well depth (if known) and
head loss. When figures are lacking or questionable, as is usually the case,
flow rate at zero pressure must be measured at the metering point by
opening the pipe line and checking the flow with a calibrated bucket
or 55-gallon drum and stopwatch. The figure thus obtained must then be
adjusted to the intermediate pressure of the hydropneumatic tank or
elevated storage. The pump manufacturer, a well-pump installer, or a sanitary
engineer should be consulted for assistance in determining the amount of
flow reduction resulting from system pressure.
Step I II: Locate space for installation of the feeder and solution tank.
If the pump and injection point are in a well house, and the well house
is spacious and dry, this is the ideal situation, for then the installation
can be neat and compact (Fig. 1). However, such is not always the case
and equipment must be placed in an adjoining building, in the school
basement, or in a small shelter built for the installation. It is preferable
to have the equipment as close to the metering point as possible.
Step l v: Determine necifications for the master meter and feeder. For
economy and best accuracy, the meter should be as small as flow conditions
will permit. However, the pipe size at the metering point and the pump
capability are also factors to be considered. If a pressure loss of several
pounds per square inch can be tolerated, the pipe can be reduced with fittings
to accommodate a smaller meter. The feeder size depends on the water flow
rate and the fluoride level decided upon, as well as on the concentration of
fluoride solution to be used. If a saturator is used, the solution produced
is approximately 18,000 ppm F, so the feeder delivery rate in gallons per
hour (gph) will be: pump rate (gph) X desired F (ppm) ! 18,000 ppm. For
example, if the pump rate is 12 gallons per minute and the desired fluoride
level is 6 ppm, the feeder delivery rate in gallons per hour will be:
12 X 60 (MinfHr )
18,000 X 6 .24 wh
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SATURATOR SUPPLY METER
FLUORIDE FEEDER
WELL PUMP
Figure 1. Pump Room
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With this figure, a feeder can be specified, bearing in mind that most chemical
feeders operate best at midrange, and that the estimate of the pump delivery
rate is subject to revision. For the low flow rates usually encountered in
school water systems, diaphragm-type feeders having resilient check valves
are usually the best choice. Because the feeder will be electrically cross-
connected to the pump circuit, an independent motor drive with 3-step
pulley will also lend flexibility to the arrangement. For simplicity in making
electrical connections, the motor should have the same electrical requirements
as the pump, for example, a 220-volt motor and a 220-volt well pump. An
electrician can identify the voltage and phase characteristics of the pump if
they are not already known. 2 ° Feeder head construction materials for
handling saturated sodium fluoride solutions are readily available.
Step V: Once the master meter and solution feeder have been specified and
obtained, installation is begun by:
(A) Opening the pipe line for insertion of the meter, injection tee, strainer,
check valve, saturator supply tee, vacuum relief valve and other fittings as
required. The fluoride injection should be at the bottom of the pipe to prevent
air binding, so it may be necessary to raise the pipe line. If insufficient space
is available for the meter and other appurtenances, a loop in the pipe line
must be made. For buried or close-to-the-floor pipe, a vertical loop will
generally be applicable (Fig. 2). The installation of shut-off valves at
appropriate points will make maintenance of the system parts more convenient.
Where the pump is a submersible type in a well, the use of pipe unions will
facilitate removal of equipment so that the well pump will be accessible for
repairs. Special conditions apply if the pump is a reciprocating type.
Specifically, with a reciprocating pump, the inclusion of a surge chamber is
a necessity to prevent damage to the meter and to permit the use of a flow
switch. A flow switch is also recommended whenever there is a distinct
possibility of pump failure and resultant fluoride overfeed. The flow switch,
in series with the feeder motor, should be set so that the circuit is broken
when the well pump delivery falls below the figure established as the normal
flow rate at the time the installation was designed.
(B) Connect a pipe line to the saturator supply tee and run it to the
saturator position, incorporating a small water meter where convenient.
A shut-off valve should be placed between the meter and the saturator to
permit manual control of the saturator supply.
Step V.1: Install the saturator so that it is level and the filling-gate is acces-
sible. If necessary, connect a drain line to the overflow. Install the feeder so
that it is above the saturator and so that the intake line is as short and
straight as possible. A small shelf a short distance above the top of the saturator
will provide a convenient base for the feeder. Cross-connect the feeder motor
electrically to the well-pump circuit so that the feeder will, run whenever the
well pump does. If a flow switch is used, connect it in series with the feeder
motor.
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VACUUM RELIEF VALVE
00
VALVE — —
FLUORIDE FEED
I II —
I II
Ii
Ii
TO STORAGE
I
LY
VALVE
UNION
ER
FROM
Figure 2. Master Meter Loop
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Step VII: After all electrical and plumbing connections are made, connect
the feeder discharge tube to the injection tee, making sure all check valves are
positioned so that fluoride solution can be fed into the line but water cannot
flow toward the feeder. Insert the suction tube into the saturator, and
inspect the check valves for proper position. The suction tube should terminate
a few inches above the bottom of the saturator and should be equipped with
a foot-valve and strainer. PrepaTe the saturator by placing gravel carefully
around the cone, adding sand, leveling the sand surface and then adding
crystalline sodium fluoride (Fig. 3). The sodium fluoride should be preferably
40 to 60 mesh, but slightly finer crystals can be used. Under no circumstances
may powdered sodium fluoride be used, since it will sift through the sand
and gravel and be pumped as a slurry. Also, water will not percolate freely
through fine powder. After leveling the surface of the fluoride layer, admit
water to the saturator and adjust the float valve so that the water cut off is
slightly below the overflow. The saturator will hold 200 pounds of fluoride,
or more, but in some cases a depression will have to be made in the surface
of the fluoride to permit operation of the float. Prime the feeder and adjust
the feed rate to correspond to previous calculations. Most small diaphragm-
type feeders can be primed by loosening the discharge cap and jiggling the
suction tube up and down. This causes liquid to rise in the suction tube until
it teaches the pumping chamber. Retighten the discharge cap and other fittings
and start the well pump. Take readings of both the master meter and the small
meter on the saturator water supply line.
Step VIII: Recheck the well-pump delivery rate, using the master meter and
stop watch through several cycles of high and low pressure. If necessary,
readjust the feeder. After a few hours of operation, sampling can begin.
Choose a sampling point where there is considerable water usage so samples
will be representative. Depending on the system layout, it may take con-
siderable time for the system to become completely fluoridated. This is
especially true when there is a storage reservoir “riding” on the system.
Fluoride concentrations should rise gradually and then reach an equilibrium.
SURVEILLANCE
After equilibrium has been reached, the desired fluoride level achieved
and the system stabilized, about 20 to 25 water samples should be taken
throughout the system and analyzed for fluoride content. These samples
can form the basis for a study of the inherent variability in the system. The
variability of fluoride concentration in the samples is used to determine
action and warning limits for a quality control chart’ (Fig. 4). The great
advantage of the quality control chart as a surveillance tool is that it is
easy to maintain. It permits historical comparisons with present observed
variability and encourages adjustment of the process when the limits are
violated. As the overall variability in the process is reduced, narrower action
and warning limits can be established above and below the desired target
level.
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SLIDING COVER
FOR FILLING
1 ‘/2’ F.P.T.
OVERFLOW
MOLDED TANK
3/si F.P.T.
DRAIN
Figure 3. Sodiuni Fluoride Saturator
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M.o n
F ppa In Sampl.s of 2
4.8
4J
4.6
4.5
::
::
:::
:::
:::
::
z-1
::
troic61e?
7 14 21
28 4
11
18
25
2 9 16 23 30
OCT.
NOV.
DEC.
S.MI-W
..kI
y Sampli
ng P .riods
4.4
4.3
4.2
Rang.
Fppm in Sampl.s of 2
1.0
0.8
0.6
0.4
0.2
0
Figure 4. Quality Control Chart, School Fluoridation
Action
Warning
Target
Level
Warning
Action
Action
Warning
16 23
OCT. NOV. DEC.
S.i-W..kly Sa.ipling Periods
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Fluoride sampling for operational control should follow a predetermined
schedule. A minimum of two samples a week is the suggested sampling freyen-
cy and one of the samples should be sent to the supervisory authority, such as
the State Health Department Laboratory, to enable duplicate fluoride analyses
to be performed. When the quality control chart reveals that the process is
relatively stable, split-sample analyses can be done less often. It is recommended
that quality control charts be kept at the f 1 uoridation site and at the location
of the supervisory authority to afford the operator and supervisory authority
an opportunity to check for trouble and take corrective action when mdi-
cated.
As with municipal fluoridation, records of both calculated and analytically
determined fluoride levels should be maintained (Fig. 5). The calculations is
simple—gallons of fluoride solution fed times concentration divided by gallons
of water pumped (Fig. 5, left band part of form). However, due to the inter-
mittent operation of a saturator, the calculated fluoride level for short periods
of time wifi seldom agree with the analysis of a spot sample. For longer
periods, the calculated level should serve as a check on analytical determina-
tions. Levels of fluoride that are analytically determined in the twice-weekly
water samples are averaged and their mean and range recorded (Fig. 5 right
hand part of form). The values are then plotted on the quality control chart
(Fig. 4).
Although routine analyses and maintenance of the system can be performed
by the local operator, some supervision is recommended. Under normal condi-
tions, the relationship between the local operator arid the supervisory
authority consists of the submission of split-water samples at prescribed
intervals and the reporting of analytical results. However, when trouble
occurs, the skill and judgment of the supervisory authority are invaluable
adjuncts toward keeping the fluoridation process operating smoothly.
MAINTENANCE AND TROUBLE-SHOOTING
The successful and uninterrupted operation of a school fluoridation
system depends first on the installation which is designed to be as trouble-
free and fool-proof as possible, and most importantly on the conscientiousness
of the person or persons assigned to operate the installation.
The operation of the saturator can be checked by taking a sample of solu-
tion from inside the cone, diluting (stepwise) down to a level within the
analytical range and performing a fluoride analysis. If the dilution is care-
fix! and the analysis accurate, a 4% sodium fluoride solution should read
from 17,000 to 18,000 ppm F. The feeder operation (against pressure)
can be checked by removing the suction tube from the saturator, inserting
it in a water-filled graduated cylinder (without losing prime) and with
the aid of a stop watch, measuring the feed rate while the water supply
pump is running.
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SCHOOL
METER READINGS
(Gallons)
WEEKLY WAT
—
ER SAMPLES
—
FIRST
SECOND
once a
6.8 ppm Fluorjd,
ppm Fluerid .
Water Saturator
3.029. /50 FF
Pv.vious .i 98Z4’ o ,66
Difference W,690
D ,._- 1’ ”70
Dot. /o/I/70_
Date
Mean ppm { ht+2nd }
2 —
0.2 (high.tt minus loweit)
REMARKS
REMARKS
SUPERVISING AGENCY
SPLIT-SAMPLE ANALYSIS
CALCULATED FLUORIDE
(Saturator dift.) = P P
(F conc.)
(Water diff.) 4’/oQO
SECOND
FIRST
6./ ppm Fluoride
J ppm Fluoride
lst+2nd}
Mean ppm
2
Rang. (l igh .st minus low.st)
Dot. /Q//2/7o
REMARKS
REMARKS
Figure 5. School Fluoridation Fluoride Analysis Form
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Besides maintaining a supply of fluoride in the saturator, keeping the feeder
lubricated and leak-free, the operator’s principal function is to maintain
the desired fluoride level within the limits established. Because a skilled
analyst is seldom available, the operator should be taught one of the simpler
methods of fluoride analysis, taking into account the funds available for
equipment, the operator’s manual dexterity and particularly, the requirement
that samples must be diluted. School fluoridation usually calls for fluoride
levels several times the optimum for the local area, but fluoride analytical
methods, except the electrode method, are limited in range so dilution of
the sample is essential. The inaccuracy of a given method is multiplied by
the dilution factor, so determinations by the most simple method, the visual
comparator, which is also the least accurate, would be totally unsatis-
factory. If the funds and skill to operate the electrode method are not
available, the next choice would be the SPADNS colorimetric procedure,
utilizing a spectrophotometer or more probably, one of the portable direct-
reading lo eters. 20 ’ 22
The possibility of designing a school fluoridation installation in which the
feed rate is automatically adjusted to water flow-rate (“pacing”) has been
considered and tried in several instances. Unfortunately, the benefits gained
have seldom justified the extra cost for equipment and the maintenance
problems have been prohibitive. The systems used were based on a meter-
contactor and solenoid-driven diaphragm feeder, or a water-driven feeder
depending on a solenoid valve for diverting water flow as required. When the
meter contactor was a mechanical switch, difficulties with sticking contacts
were experienced and although the use of a mercury switch would have
eliminated this problem, there were additional difficulties with solenoid
valves and with the electrical circuits required to operate them. The use
of motor-driven feeders necessitates the incorporation of an interval timer
into the electrical system and the timer is also subject to mechanical
and electrical failures. In general, then, for the sake of simplicity and
ease of maintenance, a motor-driven feeder without any attempt at “pacing”
is preferred.
Incorrect fluoride levels occurring in the type of installation described
can be caused by a number of factors:
1. High fluoride reading -
a. Error in fluoride analysis
b. Feeder adjustment is incorrect
c. Failure of the saturator cone
d. Sifting of sodium fluoride through the sand barrier
e. Failure or lessened delivery of the water supply pump
f. Break in a water line with the failure of a siphon-breaker or
vacuum-relief valve
g. Contamination of the sampling container
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h. Water leak between the water supply pump and injection point
i. Sample for fluoride analysis taken before thorough mixing
2. Low fluoride reading -
a. Error in fluoride analysis
b. Feeder adjustment is incorrect
c. InsuffIcient quantity of sodium fluoride in the saturator or the
fluoride is not dissolving fast enough
d. Loss of feeder prime
e. Accidental shut-off of the feeder switch or electrical failure
f. Lack of water supply to the saturator (accidental valve closing
or improper float adjustment)
g. Failure of the feeder or leaking connections
h. Air-binding in the feeder discharge line
i. Feeder check-valve failure or incorrect positioning
j. Accidental valve closing at the injection point
k. Sample for fluoride analysis taken before thorough mixing
1. System not in equilibrium
In climatic areas subject to freezing, when the installation is located in an
unheated well house or similar shelter, water meters can freeze. In such
areas, water meters with frostproof construction should be specified, and
in addition, some provisions for space heating should be made. In small
enclosures an infrared lamp is usually adequate, but for larger buildings,
a radiant panel may be required. Thermostatic control, rather than a manual
switch, will insure protection of the equipment when the temperature
drops.
SUMMARY AND CONCLUSIONS
The engineering aspects of school water fluoridation, with the exception
of maintaining a higher fluoride level, are fundamentally similar to those of
community water fluoridation. Unlike the community situation, however,
there is a general lack of knowledge of the water system characteristics by
the school personnel, and skilled operators are seldom available at the
school site. To overcome these deficiencies, a simplified procedure for
making a school fluoridation installation has been derived. The installation
is based on the use of a saturator for automatically preparing fluoride
solutions of fixed concentration. By choosing a point for fluoride injection
where water flow and pressure are relatively constant, or at least vary
only between regular limits, the need for frequent dosage adjustments is
eliminated. In addition, a system for surveillance has been established
which enables both the local operator and the supervisory authority to
detect potential problems and take corrective action when indicated. While
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both the equipment and the procedure would have wide applicability,
it is readily conceded that the widely varying conditions at each prospective
site may require further engineering consultation which could lead to an
entirely different approach.
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R eferences
1. DHEW, U. S. Public Health Service, NIH. Fluoridation Census, 1969.
GPO Publication 0-380-791, Washington, D. C.
2. ‘Ast, D. B., Smith, D. J., Wachs, B., and Cantwell, K. T., Newburgh-
Kingston Caries-Fluorine Study XIV. Combined Clinical and Roetgeno-
graphic Dental Findings After Ten Years of Fluoride Experience. J. Am.
Dent. Assoc. 52:314-325 (March 1956).
3. Knutson, J. W., An Evaluation of the Grand Rapids Water Fluoridation
Project. : Michigan Med. Soc. 53:1001-1006 (Sept. 1954).
4. Russell, A. L., and Hamilton, P. M., Dental Caries in Permanent First
Molars After Eight Years of Fluoridation, Arch. Oral Biol. (Special
Supplement) 6:50-57 (1961).
5. Arnold, F. A., Jr., Dean, H. T., and Knutson, J. W., Effect of Fluori-
dated Water Supplies on Dental Caries Prevalence: Seventh Year of
Grand Rapids-Muskegon Study. Public Health Report 68:141-148
(Feb. 1953).
6. Bushel, A., and Smith, D. J., Newburgh-Kingston Caries Fluorine Study.
X. Dental Findings for 17-Year-Old Group After Nine Years of
fluorine Experience, N. Y. Dental J. 25:215-218 (June-July 1955).
7. Hill, I. N., Blayney, J. R., and Wolfe, W. The Evanston Dental Caries
Study, XV. The Caries Experience Rates of Two Groups of Evanston
Children After Exposure to Fluoridated Water. J. Dent. Res. 36:208-2 19
(April 1957).
8. Klein, H., Dental Caries Experience in Relocated Children Exposed to
Water Containing Fluorine, II. J. Am. Dent. Assoc. 33:1136-1141
(Sept. 1946).
9. Russell, A. L., Dental Effects of Exposure to Fluorine-Bearing Dakota
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