/

IN FLOUR MILLS

U. S. DEPARTMENT OF AGRICULTURE

Agricultural Marketing Service

Marketing Research Division

Washington, D. C.
This handbook was prepared by

the Stored-Product Insects Section,

Biological Sciences Branch, Marketing Research Division, Agricultural Marketing Service. It supersedes Circular 720, "Controlling Insects in Flour Mills," prepared by

the former Bureau of Entomology

and Plant Quarantine. The Sanitation Committee, Association of

Operative Millers, collaborated in

planning this handbook, and critically reviewed the text. The Food

and Drug Administration, Department of Health, Education, and

Welfare, under whose supervision

residue tolerances for pesticides on

raw agricultural products or milled

food and feed products are established, concurs in the insect control

procedures recommended.

CONTENTS

Page

Grain supply 1

Why infested wheat is unfit for

milling 2

How to obtain clean wheat for

milling 2

Detecting internal infestation 2

Visual observation 2

X-ray method 2

Cracking flotation method 2

White flotation method 3

Grain as a source of infestation in

the min 3

Other sources of infestation in the

mill 4

Stock used for blending purposes 5

Returned flours 5

Second-hand machinery 6

Accumulated feed stocks 6

Infestation from nearby elevators - 6

Insect population in flour mill 6

Controlling the insect population

in flour mills 7

Sanitation in the mill 8

Prevention and control 8

Use of sprays in the mill 9

Keeping the tail end of the mill

free from insects 9

Handling choke-up stock 9

Page

Fumigation in the flour mill 10

General considerations 10

Protection of personnel 10

First aid 12

Preparing the mill 12

Fumigation with hydrocyanic acid. 13

Open-space application 14

Machinery-piping system 16

Fumigation with methyl bromide _ 17

Fumigation with chloropicrin 20

Local fumigation 21

Heat and cold for treating flour

mills 23

Continuous-process heat treatment

of milled cereal products 23

Insect contamination in milled

cereal products 24

Insect control in the warehouse 25

Sanitation and warehouse management 25

Fumigation 25

Bulk flour storage 26

Insect-resistant bags 26

Infestation in transit 26

Bulk transportation of flour 27

Electromagnetic energy 28

February 1958

U. S. GOVERNMENT PRINTING OFFICE: 1958

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington 25, D. C. - Price 15 cents
Scientific Names of Insects Discussed

Angoumoîs grain moth Sitottoga cerealeUa (Olîv.l

Cadelle íenefaroides maurîtankus ÍL.)

Flat grain beetle taemoph/oeus minutus (Oliv.)

Confused flour beetle Tríbolíum confusum Duv.

Granary weevil Sitophilus grananus (L.)

Lesser grain borer Rhyzopettha dominica (F.)

Mediterranean flour moth Anagasta Iciitiniella (Zeil.)

Red flour beetle Tríbolíum castanevm (Hbst.)

Rice weevil S/fophi/us oryza (L.)

INSECT CONTROL IN FLOUR MILLS

By R. T. Cotton

Biological Sciences Branch, Agricultural Marketing Service ^

Producing flour that will meet

high standards of purity and maintaining the flour in that condition

until it reaches the consumer is the

aim of the milling industry. This

handbook suggests procedures and

provides information on how to prevent insect infestation in flour mills.

Grain Supply

To produce flour of acceptable

quality it is essential to mill only

grain that is free from serious contamination by insects and rodents.

Cooperative studies between industry and the Food and Drug Administration (Harris et al.Y have

shown that a major source of contamination in flour is the wheat in

market channels. The insects that

feed within the wheat kernels are of

most concern to the miller. Insects

that feed externally may destroy

grain or cause it to heat, but they

are easily removed by the cleaning

process prior to milling.

What are the chances of obtaining milling stocks that are free

from insects that feed internally in

the kernels? The co-operative

^Dr. Cotton retired March 30, 1957.

^Harris, K. L., Nicholson, J. F., Randolph, L. K,, and Trawick, J. L. An investigation of insect and rodent contamination of wheat and wheat flour. Assoc.

Off. Agr. Chem. Jour. 35 (1) : 115-158.

1952.

studies referred to show that slightly over half of the wheat shipments

reaching the mills over a 1-year period had some degree of internal

insect infestation. The infestation

tended to be lower in the West,

Northwest, Inter-Mountain, and

Northern States—or in areas where

the wheat is predominantly hard

red spring or white wheat—than in

the Central Plains States where

hard red winter wheat is predominant. It was highest in the soft

red winter wheat from the Midwestern and Eastern States.

Insect infestation in wheat increased as wheat moved from the

farm to the terminal elevators. In

market wheat the infestation from

May to September was low during

the marketing of the new crop.

The level began to increase in September and continued to do so

through the winter.

Wheat coming from the field is

practically free from insect infesta1
tions. These occur later—in storage, transportation, and milling.

Why Infesied Wheat Is Unfit for

Milling

The grubs, or larvae, of insects

such as the rice weevil, granary weevil, lesser grain borer, Angoumois

grain moth, flat grain beetle, and

occasionally the cadelle or flour

beetle burrow inside the wheat kernels, and they and their contamination cannot be entirely removed by

any practical known method. The

cooperative studies showed that in

16 flour mills the insect fragment

count in flour produced in the mills

was closely related to the infestation inside the wheat that was

milled. The effect of wheat cleaning on the reduction of insect contamination varied from mill to mill.

The over-all reduction was about

one-third, but in individual mills

the reduction varied from none to

more than 50 percent.

How To Obtain Clean Wheat for

Milling

Wheat at harvest time is usually

free from contamination by insects.

The ideal procedure for a mill

would be to buy a year's supply of

wheat at harvest, place it in clean

elevator storage, and fumigate the

wheat as a precautionary measure.

Obviously it is not possible for most

mills to follow this plan owing to

the limited storage capacity of their

elevators. From 4 to 20 times the

storage capacity of a mill elevator

may be required to supply the

wheat needed for keeping the mill

in operation. Therefore market

wheat being bought should be thoroughly tested to determine whether

or not it is sufficiently free from insect and rodent contamination to

be fit for milling. Many methods

of determining dangerous amounts

of internal insect infestation have

been developed from time to time.

The more important ones are discussed below.

Detecting Internal Infestation

In general it has been found that

wheat with more than 0.5 percent

of infested kernels is unfit for milling. For domestic flour production some mills will not use wheats

for their mill mixes that contain

more than 8 internal insects per

100 grams.

Visual Observation

In wheat containing appreciable

insect infestation there are usually

enough kernels showing emergence

holes or insect damage that an experienced grain man can determine

the degree of infestation by looking at a sample.

X-Ray Method

The most accurate and widely

used method of determining the extent of internal insect infestation

in samples of grain is by the use of

X-rays.^ X-ray machines are used

to take radiographs of 100-gram

samples of wheat that reveal insect

forms within the kernels. Manufacturers have now developed Xray units specifically for this purpose. Although equipment and

continuous operation are rather expensive, the method is being used

extensively by large milling concerns.

Cracking Flotation Method

Another method of determining

the amount of internal insect infestation in grain is the "Cracking

' Nicholson, J. F., Müner, M., Munday,

W. H., and others. An evaluation of five

procedures for the determination of Internal insect infestation of wheat. V.

The use of X-rays. Assoc. Off. Agr.

Chem. Jour. 36 (1) : 150-155. 1953.
Flotation Method."* Cleaned

grain is coarsely ground to release

the internal insects and is either

soaked in a water-alcohol mixture

or in boiling water and then mixed

with gasoline or mineral oil. The

insects are floated off with the oil

layer in a Wildman trap flask and

collected on a filter paper and

counted. In the process of grinding, some of the insects are broken,

but characteristic parts such as the

heads can be counted and the number of whole insects reliably estimated.

Whife Flotation Method

More recent studies by White ^

indicate that a mixture of two solutions of different specific gravities

can be used in making a rapid separation of infested from noninfested

kernels in a sample of wheat. The

mixture consists of a solution of

sodium silicate (NaaSisO?) in water

with a specific gravity of 1.160, to

which is added methyl chloroform

adjusted to a specific gravity of 1.30

with refined kerosene. When placed

together a definite separation layer

is formed between the two liquids,

the lighter sodium silicate solution

remaining on top. Kernels containing late stages of weevil larvae float

on top of the sodium silicate solution ; kernels containing early

stages of weevil larvae and some

noninfested lightweight kernels are

buoyed up to the separation level of

the two liquids; and noninfested,

normal-weight kernels sink to the

bottom. A 1,000-kernel sample is

placed in a beaker of the mixture

and stirred ; as the kernels get wet,

they quickly separate. If no kernels

come to the top, the sample can be

considered free from serious infestation. If there are any floaters, the

degree of infestation can be estimated by the relation between the

number of floaters and the size of

the sample.

Grain as a Source of Infestation in the Mill

Of the many sources of insect infestation in the flour mill, the grain

stream is usually the most important. Grain coming to the mill is

often infested, although the degree

of infestation varies with the location of the mill and the source of

the grain. Mills in the springwheat region and in the Pacific

Northwest have fewer insect

troubles than mills in the Southwest, where as many as 30 different

species of grain-infesting insects

have been found in grain arriving

at the mills. The fact that many

mills find it necessary to draw wheat

from man}^ sources to meet their requirements often complicates their

insect problem considerably.

^ See footnote 2, p. 1.

^W^hite, G. D. Studies on Separation

of W^eevil-Infested from Noninfested

Wheat by Flotation, AMS-101. 10 pp.

March 1956.

Grain-cleaning machinery now in

use does not completely remove insects from the incoming grain.

Figure 1 shows that samples from

the wheat elevator boots, which

handled the wheat after it was

cleaned, had a high average insect

population. As cleaned wheat is

not a preferred food for the grain

beetles, it is believed that they are

introduced into the elevators with

the wheat stream. These insects

spread all through the mill and are

an important source of infestation.

Previous investigations have

shown that some insect forms can

pass uninjured through the entire

system of rolls. Adults of the confused flour beetle have passed unharmed through the first three

breaks, and partly grown larvae

have survived passage through the

first three middling rolls. Eggs of

this species are so small that many
■■n

AVERAGE NUMBER 0 F INSECTS PER a-OUNCE SAMPLE

Ei3 fLM CR»,N fl£ TLE W^ CiOELLE

^ GR.m «EEV,tS 1=) t?SSé"/eîre

CZD 'LL OTHERS

AMS Heß. ii321-57(7)

Figure 1.—Average number of insects per 8-

ounce sample and proportions of different

species found in 2,367 samples from the

different milling streams of 17* flour mills

in Kansas, Oklahoma, and Missouri during a

1-year period (1934-35).

of them survive passage through the

low-grade flour rolls. When these

eggs hatch, infestations may quickly

reach serious proportions in all

streams of the milling unit.

Figure 1 also shows that wheat

screenings from the elevator are

usually heavily infested. In many

mills the cleaning machinery is

placed close to the milling units, and

often the screenings are spouted to

a collecting sack near the milling

machinery or stored finished flour.

Any insects crawling from these

screenings have easy access to the

milling machinery or finished flour.

Grain-cleaning machinery should

be segregated in a smut room at one

end of the mill, and grain screenings

should be disposed of immediately

by spouting to a screenings hammer-mill, a centrifugal-force machine, or to a vault where they can

be fumigated. If one of these procedures is followed, treated screenings fed into conveyors or transferred to the tail end of the mill will

not serve as a source of contamination to the flour-producing section.

Grain screenings should never be

allowed to accumulate in the mill or

in the flour warehouse.

Centrifugal force can be used to

advantage in the mill to destroy

infestation in both dry and tempered wheat (fig. 2). The machine

consists essentially of a rotor with

a series of hardened steel impactor

posts mounted on it perpendicular

to its face. The rotor is mounted

directly onto the shaft of an electric motor, and is enclosed in a housing. The grain is introduced near

the center of the rotor, which revolves it at a high speed on a horizontal plane, and hurls it by centrifugal force against the impactor

posts and the housing. In the operation, free-living insects are

killed and some of the infested kernels are broken open so as to expose

the internal infestation. A scourer-aspirator removes dirt, debris,

and insects dislodged by the impact.

In treating dry wheat a slowspeed unit (1,750 r. p. m.) is located beyond the receiving separator in the cleaning section. This

unit destroys and removes most of

the external insect life and removes

foreign material from the grain.

In treating tempered wheat a highspeed unit (3,500 r. p. m.) is located just before the first break rolls

and serves as a final cleaning operation. At this speed infested kernels are broken open and the internal infestation largely removed.

Other Sources of infestation ¡n the Mill

Aside from the grain stream,

there are a number of other sources

of infestation, such as blending

stocks from other mills, returned

flours, second-hand machinery, accumulated feed stocks, and nearby

elevators.
Figure 2.—A mechanical bulk-flour centrifugal machine.

Stock Used for Blending Purposes

The demand for blended flour by

large baking concerns necessitates

the use of large quantities of clear

and low-grade flours that mills may

obtain in part from their own warehouses and in part from other mills.

Usually these flours have accumulated over a period of time and,

since they are highly preferred by

the insects, are frequently infested.

Stock intended for blending

should first be examined to determine whether it contains insect contamination. Insect excrement in

flour cannot be removed by any

practical rebolting process, and

flour that contains an appreciable

infestation of insects is considered

unfit for human consumption and

should be diverted to feeds.

Flour intended for blending

should be run through a sifter

clothed with number lOXX bolting cloth and then through a treating machine using centrifugal

force, as a precautionary treatment

to remove or destroy any insect life

that might later start an infestation. The overs should also be

treated with centrifugal force before being spouted to feed.

Returned Flours

Returned flours are always a

problem to the miller because they

invariably constitute a serious

source of infestation. Formerly

these were fed back into the mill

and incorporated into one of the

many blends required by modern

markets. If, as was usually the

case, these flours were infested, the

same difficulties were experienced as

are described in the preceding section when infested clears are used

for blending.

Returned flour that is infested

should be sterilized by heat, treated
by centrifugal force or by some

other accepted method, and diverted

to feed immediately. It should

never be stored even temporarily in

the mill or flour warehouse.

Mills that deliver by truck encounter the problem of providing

for the return of infested flours

during their regular delivery trips.

If freshly milled flours are placed

in the same truck with infested

flours, they are likely to become infested also. Not infrequently, insects crawling from the infested

products are delivered to customers

along with fresh stocks of flour. If

returned flour products must be

picked up in the course of a delivery trip, provide the truck with a

separate compartment into which

these products can be placed, thoroughly clean the truck between

trips, and burn or otherwise treat

the sweepings so as to destroy the

insects they contain. Feed and

flour should never be delivered in

the same truck.

Second-Hand Machinery

Used machinery occasionally is

purchased from mills that are being dismantled. All milling units

are likely to contain some infestation, and machinery that has been

lying idle for some time is almost

sure to be heavily populated with

insects, because they thrive and reproduce rapidly in undisturbed accumulations of milling stock. Unless proper precautions are taken,

used machinery may introduce insects into a mill. Infestations of

the Mediterranean flour moth are

known to have been frequently carried from one mill to another in this

way.

If possible, second-hand milling

machinery should be fumigated in

an atmospheric vault, under a tarpaulin, or in a railway box car before it is set up in its new quarters.

Accumulated Feed Stocks

The practice of storing certain

feeds in the mill or flour warehouse

during periods when such feeds are

accumulated is exceedingly common. It is difficult to produce feed

that is entirely free from insect infestation, owing to the impossibility of sifting it through fine enough

mesh to remove insect life. If

feeds are stored near flour or milling machinery, insects are sure to

migrate from the feeds.

Feeds can be treated by centrifugal force in such a manner that all

insect life is killed, but unless mills

are equipped for this, the feeds

should be stored in a separate warehouse as far as possible from the

mill and the flour warehouses. Of

course, warehouses should be kept

sanitary.

Infestation From Nearby

Elevators

Many of the insect pests of stored

grain and milled cereal products are

strong fliers. During grain-cleaning operations it is not uncommon

for insects removed in the process to

be blown out into the open air.

Many of these insects will fly from

elevator to flour mill, where they

will start infestations in elevator

boots or in any milling unit into

which they can crawl. The red flour

beetle and the flat grain beetle are

the two species most likely to come

from such sources. Insects removed

in grain-cleaning operations should

be destroyed immediately.

Insect Population in Flour Mill

The insect population of a flour

mill is of vital concern to the miller,

because his ability to produce insect-free flour is closely related to

the absence of insect population in

the milling streams.
Information relative to insect

populations in milling machinery

at different times of the year, and as

affected by different methods of

milling and insect sanitation, has

been obtained through monthly collections of samples of stock from a

number of mills over a period of

several years. Of 2,367 8-ounce

samples of stock taken from elevator boots or purifier conveyors during 1934-35, 80 percent were found

to be infested (fig. 1). In these

samples 74,175 insects, representing

AMS Neg» l4322-S7(7)

Figure 3.—Percentage of different species of insects taken in milling streams of 17 flour

mills in Kansas, Oklahoma, and Missouri

during a 1-year period (1934—35).

30 species, were found. The relative

abundance of the 6 species occurring most frequently is shown in

figure 3. The flour beetles {TriboZm77i spp.) were predominant. The

relative abundance of insects in the

various milling streams, as shown

in figure 1, is attributed to the relative attractiveness and nutritional

value of the various milling fractions. The heaviest populations are

found in low-grade flour.

The Mediterranean flour moth

was formerly the most troublesome

pest of flour mills, owing to its

abundance and the habit of the

larvae, or worms, of spinning silken

threads wherever they crawled,

webbing and matting the flour

particles together and clogging the

machinery until operations had to

be shut down. Although this insect is no longer a serious pest in

mills that fumigate annually, it is

still common in some mills.

Any species of insect that attacks

grain may be found in a flour mill.

These insect pests of stored grain

are described and figured in U. S.

Department of Agriculture Farmers' Bulletin 1260 (revised 1955), a

copy of which may be obtained by

writing to the Office of Information,

IT. S. Department of Agriculture,

Washington 25, D. C.

Controlling the Insect Population in Flour Mills

Insects will breed in any location

where accumulations of flour, grain,

or other milling stock remain undisturbed. The miller must eliminate su(îh accumulations or treat

them with fumigants.

Double floors or walls provide

harborage for insects making them

difficult to eliminate. Poorly designed milling units also create

problems. Danger spots are elevator boots ; conveyors for flour, grain,

or dust; conveyors on reels and

purifiers; dead spouts and conveyors ; dust-collecting systems in general; and the bottom and idle sections of certain types of sifters. A

certain amount of stock remains

undisturbed in these milling units.

Redesigning milling equipment

or replacing it with more modern

machinery will do much toward

eliminating insect breeding places.

A pneumatic conveying system for

mill stock solves many of the problems of keeping a mill clean and

sanitary. Pneumatic lifts require

far less floor space than elevator

legs and can be located alongside

the walls. The space formerly taken

up by elevator legs can be used for

additional machinery.

445005°—58-
Conveyors on reels and purifiers

should be replaced by hoppers.

Dust-collecting systems require

constant attention. Many are poorly designed, quickly become chokedup, and allow infestations in the

stock in these systems to crawl back

and infest all milling units. Systems in which settling chambers are

eliminated are preferred. Enclosed

stocking-type dust collectors that

permit rapid effective fumigation

are highly desirable from the standpoint of insect control. The system

must be cleaned out regularly.

Elevator boots should be changed

to the rounded-bottom type raised

above the floor. This will eliminate

most of the excess milling stock and

prevent insects from crawling from

one boot to another.

In modern concrete mills with

concrete floors and walls, the problem of mill sanitation is not so difficult as in an old wooden mill.

Every effort should be made to

eliminate dead spaces in walls and

floors where dust and flour can accumulate. Double, hollow walls

and partitions should be eliminated.

If floors are of wood, all cracks

should be filled. Old wooden floors

or badly worn concrete floors that

are difficult to keep clean can be

renovated by application of quicksetting plastic over the old surface.

Surplus flour-handling equipment, and all other unused machinery likely to harbor insects, should

be disposed of.

Sanitation in the Mill

A good sanitation program

should be followed in every mill.

One man should be designated to

see that the mill is kept clean and

sanitary and to study ways and

means of eliminating trouble spots.

Daily inspections should be made,

starting with the mill elevator and

continuing through all floors of the

mill and flour warehouse. Care

should be taken to see that there

are no leaks in grain or flour-handling machinery, or thatleaky milling units are repaired; that the

floors and hard-to-reach places are

kept clean by the sweepers ; that unused machinery, lumber, and other

materials likely to collect dust are

disposed of; that dead stock does

not accumulate under milling units

or other stationary objects, on

beams, ledges, or other places ; that

insects are not breeding in elevator

boots, conveyors, or other machinery where dead stock occurs; that

dust-collecting machinery is functioning properly and is not choked.

A more mechanized system of cleaning flour mills is highly desirable.

A proper combination of vacuum,

mechanical floor sweepers, and judiciously used compressed air jets

must be used if sanitation in the

milling industry is to become more

effective and economical in comparison with other industries.

Prevention and^ Control

In spite of every precaution some

insect infestation will show up in

every mill. Conditions in the flour

mill system are ideal for insect development, so that an active control

program must be established and

maintained in every mill to hold the

insect population to negligible proportions at all times. The following program, if adhered to, can be

depended upon to give satisfactory

results.

A general fumigation with

methyl bromide, hydrocyanic acid,

or chloropicrin once a year during

July or August, supplemented with

the local fumigation of milling

units every 2 weeks, and the biweekly removal of milling stock

with a heavy-duty vacuum cleaner.

If it is impossible to adhere to

this program during periods requiring continuous operation of the

mill, considerable relief from infestation may be obtained by regular

use of the heavy-duty vacuum

cleaner in cleaning out dead stock

in milling units during short pe8
riods of "down" time for necessary

mill repairs. This operation will

not require the amount of time

needed for local fumigation. Certain heavily infested individual machines can be stopped long enough

to vacuum-clean them.

Use of Sprays in the Mill

Insecticidal sprays are a very useful part of any mill sanitation program, but their use must be carefully controlled as it is mandatory

that no insecticidal residues appear

in the milled products. Synergized

pyrethrum or allethrin are effective

as contact sprays against mill insects and can be safely used inside

and outside milling machinery.

When stock is removed from milling units by vacuum cleaning, many

millers follow up with pyrethrum

spray. Many formulations are

available commercially and they

should be used as directed by the

manufacturer. Itis suggested that

other insecticides used as residual

sprays on walls and floors be limited to those approved for use on

or around grain.

Keeping the Tail End of the Mill

Free From Insects

The main bolters act as a natural barrier against insect infestation entering the tail end of the

mill, as the sifter screens through

which all flour must pass before it

enters the flour-collecting conveyors are clothed with silk bolting

cloth fine enough to remove all insect life. Occasionally, however,

breaks in the silk bolting cloth allow insect infestation to pass into

the flour-collecting conveyors.

Furthermore, whenever sifter sections are opened for inspection or

repair, infested tail-overs may drop

into the flour spouts and into the

conveyors unless the sifter socks are

first removed. When making these

inspections and repairs, remove the

lower sifter socks first, and place

a close-fitting metal cap over the

sock connection with the slide spout,

until repairs have been completed

and sifter sections have been thoroughly cleaned.

If infestations are allowed to

build up without restraint in milling units in front of the main bolters, the danger of insects getting

past the bolters by the avenues mentioned will be increased. When

insects are abundant in any part of

the mill they will migrate, and if

flour conveyors are of wood or not

entirely tight, insect infestation

will result from the entry of these

migrating insects or their progeny.

The introduction into mixing conveyors of clear, low-grade, and returned flours from rebolt reels is

also an important source of infestation in the tail end of the mill.

Such stock should be given a precautionary treatment before it is

used for blending purposes.

Sweepings should be directed

through a "shoe" or small sifter to

remove foreign material and then

treated by centrifugal force before

being introduced into feed.

A centrifugal force machine (fig.

2), used alone or in conjunction

with sifters, will j)rovide added

protection against infestation in

finished flour. One of these machines can be installed directly in

the top of packer bins, or outlet

spouts from it can be directed to

one or more bins as desired.

Handling Choke-up Stock

Clean choke-up stock fed into the

head of the mill, usually into first,

second, or third break, is picked

up in sacks and may be stacked

temporarily next to sweepings.

This stock should be directed

through a "shoe" or small size sifter

and then treated with centrifugal

force before being fed back into the

mill.
Fumigation in the Flour Mill

At times all mills become so infested that simple sanitary measures are insufficient and more effective treatments, such as fumigation

or heating, are necessary.

General Considerations

The fumigation of flour mills and

warehouses is a specialized operation, the success of which is dependent on the care and skill with which

it is accomplished. Owing to this

fact and also because the fumigants

used in the work are highly toxic to

humans and dangerous to handle,

it is usually best to have general

mill fumigation done by professional fumigators. Keliable fumigating concerns are usually available in all parts of the country and

on reasonably short notice, and

render good service for a moderate

price. Some of them specialize in

mill fumigation and are particularly well equipped for it. For certain

types of fumigation large concerns

may wish to keep a corps of specially trained workers.

Success in the fumigation of any

building depends on the proper

preparation of the building itself,

the choice of the fumigant, its

proper application, and favorable

weather conditions. Since insects

are more susceptible to fumigants

when temperatures are high and

fumigants are correspondingly

more active and efficient, better results will be obtained when the temperature is 75° F. or higher. If

possible, conduct the fumigation

when there is little or no wind, as

a heavy wind will cause the fumigant to drift over to one side of the

building, leaving an inadequate

concentration at the other side.

It is desirable to obtain the maximum concentration of a fumigant

in a building at the earliest possible

moment. If the concentration

builds up slowly, the natural leakage may be great enough to prevent

an effective concentration from ever

being attained.

Before starting to fumigate,

notify the local police and fire

departments as well as security

organizations in writing. In most

large cities a permit must be obtained. Search the entire mill to

make certain that no visitors or

workmen are still on the premises,

lock all entrances, and put up

warning signs. Adjoining buildings, if any, should be vacated.

After the fumigant has been

introduced, post watchmen to

prevent the entry of people who

do not know the building is under

fumigation.

At the end of the exposure

period, ventilate the building

thoroughly by opening doors,

windows, and ventilators. This is

usually accomplished by men

wearing gas masks, although

sometimes doors and windows

can be opened from the outside.

In all fumigation operations it is

well to have men working in pairs

so that in case of accident, one

man may be able to help the other

and perhaps even save his life.

Watchmen must be particularly

vigilant to prevent bystanders or

workmen from entering until all

danger from the fumigant has

been removed.

Protection of Personnel

Every precaution should be taken to avoid exposure of the operators to heavy concentrations of

fumigants. If the operators must

expose themselves to the vapors,

or must enter a building being

fumigated to open it up for ventilation or any other purpose, they

must wear gas masks.

Always have an adequate oxygen

resuscitator available in case of

emergency.

10
There are two general types of

gas masks. One has a facepiece

and a supply of oxygen or compressed air provided from a pressure cylinder carried on the operator's back (similar to those used

in "skin-diving"), or from a remote source through a hose line.

The other, which is most frequently

used, has a facepiece and a canister.

Gas-laden air is drawn through the

canister and the gas removed by filtration. The facepiece of rubber

or rubberized fabric can be adjusted

to fit tightly across the forehead,

along the cheeks, and under the

chin, and is connected by a short,

flexible, noncoUapsible tube to a

sheet-metal canister containing absorbent materials. A light harness

or knapsack is provided to suspend

the canister from the shoulders or

to strap it to the chest. The facepiece is provided with shatterproof

glass eyepieces and with a check

valve through which exhaled air

escapes. At the bottom of the canister is a check valve, which opens

only to admit air.

Some canister types of masks

have the facepiece reduced to a

mouthpiece and a nose clamp. The

wearer breathes through a rubber

device inserted and held in the

mouth. This type does not protect the eyes from irritating gases

and is not recommended.

For each of the gases likely to be

encountered in fumigation work, a

special canister is available. Most

canisters are charged with materials intended to absorb only a limited number of closely related gases,

although the all-service canister is

designed to afford protection from

a combination of gases. A color

code has been adopted by the Bureau of Mines whereby canisters designed for different gases are assigned a specific color, e. g., a white

canister gives protection against

low concentrations of acid gases

such as hydrocyanic acid and sulfur dioxide; a black canister,

against organic vapors such as carbon disulfide, carbon tetrachloride,

chloropicrin, ethylene dichloride,

and methyl bromide; a yellow canister, against a combination of acid

gases and organic vapors ; and a red

canister against a combination of

gases. A list of gas masks of different makes that have been approved by the U. S. Bureau of

Mines is given in Bureau of Mines

Information Circular 7636, and is

available free from their Pittsburgh, Pa. (Zone 13) office.

Before using a canister-type gas

mask in fumigation work, the operator should realize that it has certain limitations. (1) A mask of

the type described above cannot

be safely used in an atmosphere

seriously deficient in oxygen. A

gas mask ceases to be adequate if,

in the presence of an excess of a

simple asphyxiant gas, the oxygen

content of the air falls below 14

percent, even though it removes any

toxic gas present in the respired

atmosphere. Not enough oxygen is

available to support life. (2) The

ordinary gas mask does not afford protection against heavy

concentrations of a fumigant

such as might be encountered in

a grain bin or atmospheric vault

under fumigation. Most canisters are designed to protect against

concentrations of less than 2 percent of toxic gases in the air. In

ordinary mill fumigations, concentrations heavier than this are not

usually encountered. (3) The life

of the canister is limited ; it can

absorb just so much gas and then

must be changed. A good practice is to discard canisters after

one-half hour of actual use in air

containing a toxic gas. Each canister should be marked to indicate

the total period it has been used.

Unless a gas mask fits tightly,

is free from defects, and does not

leak, it is useless. Before entering a gas-filled room, an operator

should be sure that the mask is caren
fully fitted to the face and head,

that it is securely fastened, and that

there are no leaks. On first entering a gas-filled room while wearing

a gas mask, he should make sure

that there is no odor of the fumigant. If any odor is detected, he

should leave the building immediately and determine the trouble.

It must also be realized that

fumigants can be absorbed directly through the skin. Do not

take for granted that the wearing

of a gas mask will afford complete protection. Heavy gas concentrations are particularly dangerous, and care should be taken

to avoid exposure to them, even

though a mask be worn.

First Aid

In case of poisoning by toxic

gases or asphyxiation due to lack

of oxygen, a doctor should be

summoned as quickly as possible.

Forbes and Grove ^ suggest the following treatment :

1. Remove the victim to fresh

air as soon as possible.

2. If breathing has stopped, is

weak and intermittent, or is present in only occasional gasps, give

artificial respiration, preferably

by the prone-pressure method,

until normal breathing is restored or until it is definitely believed that the heart action has

stopped.

3. Aid circulation by rubbing

the limbs of the victim and keeping the body warm with blankets

or hot-water bottles.

4. It cannot be emphasized too

strongly that inhalation of pure

oxygen or 5 to 7 percent of carbon dioxide and 95 to 93 percent

of oxygen, beginning as soon as

^Forbes, J. J., and Grove, G. W. Protection against mine gases. U. S. Bur.

Mines Miner's Cir. 35, 52 pp., iUus. 1954.

(For sale by the Superintendent of Documents, U. S. Government Printing Office,

Washington 25, D. C. Price 55 cents. )

possible and continuing for 20 to

30 minutes in mild cases and as

long as 1 to 2 hours, if necessary,

will be helpful in gas poisoning

or asphyxiation.

5. Keep the victim lying down

so as to avoid a strain on the

heart; later give him plenty of

time to rest and recuperate.

Preparing the Mill

Sealing

The effectiveness of a fumigation

depends largely on the tightness of

the building. Instead of each floor

being fumigated separately, the entire mill should be considered as

one unit, because inspection and observation after fumigation have

shown that many insects can survive in the sacking or other material used to plug openings running

from floor to floor. All windows

should be tightly wedged or sealed,

and any broken panes should be replaced. Loosely fitting window^

sashes should be sealed with paste

and paper, or "puttied up" with

flour and oil mixed to the consistency of putty. For stripping

window frames that are only slightly loose, several types of material,

such as masking tape, strips of

newspaper smeared with grease or

pasted with flour paste, or rolls of

unsterilized adhesive tape, can be

used. When it is impossible to

tighten a window by the ordinary

method of sealing or stripping, it

is necessary to seal the entire aperture. For this purpose car-lining

paper can be used.

Small doors leading to the exterior of the building can be tightened with any of the materials used

for the windows. Large sliding

metal or wooden doors that fit imperfectly can be calked up with the

flour-and-oil mixture or with a

paste composed of 4 parts of asbestos to 1 part of calcium chloride

mixed with a little water. Either

of these mixtures will form an effec12
tive seal yet can be easily removed

after fumigation.

For sealing ventilators on the

roof, use laminated paper, three

thicknesses of heavy paper covered

with sacking or canvas and well

pasted and tied, or covers made of

plastic film. Wherever possible,

remove the mushroom-shaped cap

of the ventilator and replace it with

a metal cap, which fits the cyclone

exhaust pipe snugly.

Cleaning Operations

Before Stopping the Mill

1. Shut off feed (wheat) at mixing bin.

2. Continue running all machinery until material is emptied

from spouts, elevators, rolls,

sifters, reels, purifiers, feed

dusters, suction trunking, and

dust collectors.

3. Remove elevator-boot slides

and station men along the boots

to keep stock pulled out where

belt cups will not carry it up

in its natural course.

4. Meanwhile, hammer elevator

legs, machinery, frames, tubular dust collectors, and spouts

with a rubber mallet or other

device that will not bruise or

injure the equipment.

After Stopping the Mill

1. Start the entire clean-up crew

at the top of the mill and work

downward.

2. Open all machines, conveyor

boxes, and flour bins.

3. Clean out suction trunks, conveyors, and dust-collector systems.

4. Examine settling chambers of

dust collectors and clean out all

accumulations.

5. Open dust collector, back drafts,

main trunks, and hand openings.

6. Loosen all sifter doors to permit

entrance of gas during fumigation; remove sieves and stack

same on the floor.

7. Clean out accumulations from

bottom section of the bran

duster.

8. Remove covers of all conveyors,

making certain that all deadend spaces are readily accessible.

9. Thoroughly clean all conveyors,

including dead-end spaces.

10. Remove adjustable feed gage

above grinding rolls and clean

out accumulations above rolls

and feeders.

11. Leave every machine open ; also

all hand openings to spouts, elevator legs, and similar places.

12. Give special attention to the

cleaning out of dead spouts or

conveyors, especially the corners.

13. Remove accumulations of stock

from elevator boots.

14. Remove to the fumigation vault

all infested materials accumulated in cleaning the mill.

15. Remove all bags or other materials used to plug spouts.

16. Seal roof ventilators or replace

mushroom-shaped caps with a

tight metal cap^

Fumigation With Hydrocyanic Acid

Hydrocyanic acid has been used

extensively as a fumigant for flour

mills for many years. Itis particularly well adapted for this type of

work because many mills are not

built to hold a gaseous fumigant for

any extended period and only a gas

that acts quickly can be effective.

Hydrocyanic acid gas kills with

great rapidity; therefore, notwithstanding the fact that all the gas

may be lost in a short time, a nearly

perfect kill may have been obtained.

Several methods of fumigating

with hydrocyanic acid have been

developed, all of which have their

13
application. Of the various methods of generating the gas, that of

vaporizing liquid hydrocyanic acid

is used most extensively.

Liquid hydrocyanic acid (96-98

percent HCN) is marketed in cylinders ranging in capacity from 30

to 75 pounds. There are several

ways in which liquid hydrocyanic

acid can be used, all of which are

effective.

Open-Space Application

The method by which liquid hydrocyanic acid is most commonly

used in the United States consists

in forcing it into the open space of

a flour mill through a system of

metal piping equipped with spray

nozzles. The cylinders containing

the gas are attached to a manifold

on the outside of the building and

the fumigant is forced into the piping system by means of compressed

air (fig. 4).

Piping the Mill

In mills fumigated by the liquid

method a permanent system of piping is often installed. Either brass,

copper, or certain plastic piping is

recommended. Iron piping is less

expensive, but because of its tendency to rust and cause clogging of

the spray nozzles it is less desirable.

A flexible copper tubing %-inch in

diameter costs about 13 cents a foot.

Since it can be readily bent, elbow

fittings are unnecessary, and compression couplings can be used, except at the main inlet, where the

cylinders are connected.

In normal times most mills can

be piped with copper tubing at a

cost of 25 to 30 cents per 1,000 cubic

feet of space, including cost of material and installation. Brass tubing costs several times as much as

copper. Commercial fumigators

are usually equipped with sufficient

reinforced rubber hose so that they

can introduce the liquid hydrocyanic acid through hose if a piping

system has not been installed. The

hose is laid on the floors of the mill

and spray nozzles are connected in

whenever desired. A line of hose is

run from each floor to a point outFigure 4.—Liquid hydrocyanic acid being pumped into a flour mill undergoing fumigation.

14
side the building where it can be

connected to a cylinder of gas.

In large mills with several floors,

where numerous branch lines are

used, each floor should be provided

with a separate riser. At least one

spray nozzle should be provided for

every 10,000 cubic feet of space, and

it is generally advantageous to use

more than this. The piping system

should be so arranged that the pressure of the gas will be approximately the same at all nozzles, thus

insuring an even distribution of the

gas. Each riser is connected with a

special inlet pipe leading through

the outside wall of the building.

Piping plans are usually designed

by an employee of the fumigating

company after he has surveyed the

building. Should blueprints of the

mill or rough sketches and measurements be forwarded to one of these

companies for making piping plans,

be sure to show offsets and whole or

part partitions. Note any other

special condition, such as heavily

infested machinery, rows of packing machines, or other places of

heavy infestation, so that an extra

spray nozzle may be added at this

point if it is thought advisable.

There should not be more than 10

spray nozzles to each riser. Where

grain or flour bins are piped, a

separate riser for these bins should

be used.

Reinforced rubber hose is used

to connect the cylinders to the

piping system. This hose must

be kept in good condition, since

there is always some danger that

the weakened hose may burst

under pressure and shower the

operator with the deadly fluid.

Before applying the material,

take care that all connections outside the building are tight.

Should a leak develop where the

hose from the cylinder is

attached to the piping, the connection can be tightened with

reasonable safety if the operator

wears a gas mask and is careful

that the liquid does not spray

his clothing. Operate the pipe

wrench with the handle above the

connection instead of below it, so

the material will not run down

the handle onto the arms and

clothing. If in doubt whether

the spray has reached the clothing, or if the liquid has run down

the arms and possibly onto the

shirt or coat, remove the clothing

and wash the hands and arms

before removing the mask.

Applying the Gas

Each cylinder of liquid hydrocyanic acid is supplied with an inlet

and an outlet valve. The outlet

valve is attached to a steel tube connected with the bottom of the cylinder. The inlet valve leads directly into the top of the cylinder,

and through it air is pumped by

means of a compressor, until a pressure of about 100 pounds is obtained. The outlet valve, which in

the meantime has been connected

with the inlet pipe to the building,

is then opened and the liquid is

forced into the building. The pressure must be maintained until all

the liquid has been blown through

the pipes into the building. The

pipelines are then blown clear and

the inlet pipes capped.

Removal of Spray Nozzles

After the fumigation and after

the building has been well ventilated, the spray nozzles should be

removed for storage and the pipes

should be capped. While removing spray nozzles the operator

should take care to prevent any

liquid, which sometimes remains

in the pipe, from dropping onto

the face or other parts of the

body. He should never stand directly under the nozzle while removing it. Should any liquid

hydrocyanic acid be lodged behind the nozzle, a decided cooling

effect will be noticed while the

nozzle is being unscrewed. It is

15
best to use a gas mask in this

work.

Special pressure nozzles which do

not clog and need not be removed

are now on the market.

Dosage Rate

The dosage will depend on the

construction of the mill and the

degree of penetration desired. In

general, 8 ounces of liquid hydrocyanic acid for each 1,000 cubic

feet of space will give excellent results. Ordinarily the gas is evenly

distributed on all floors, but a larger

quantity should be used on floors

that contain more machinery than

others.

Experimental work has shown

that if the mill is of modern concrete or brick construction much of

the labor of preparing the mill for

fumigation may be avoided by increasing the dosage to 16 ounces

per 1,000 cubic feet of space. Aside

from sealing up the building and

opening up the machinery according to directions, no other preparations are necessary. The extra gas

introduced will ensure the penetration of stock in the various milling

units.

Machîneiy-Pîpîng System

A refinement in the fumigation

of flour mills with liquid hydrocyanic acid consists in applying the

liquid fumigant directly into the

milling units by means of a series

of pipe lines (figs. 5 and 6). By

using spray nozzles that open when

a uniform pressure is obtained

throughout the system, equal quantities of fumigant are supplied to

each milling unit. The spray nozzles are so constructed that when

the pressure is removed a flexible

diaphragm recoils, the holes in the

diaphragm through which the fumigant is discharged being closed

by a central pin. This prevents

foreign matter from plugging up

the nozzles between fumigations.

AHS Neg. U323-57(7)

Figure 5.—Method of piping machinery in a

flour mill for fumigation with liquid hydrocyanic acid. Cleaning house.

As is the case with the open-space

system, the gas is applied from outside the mill. A considerable saying in cost is effected by using this

method, as a much smaller quantity

of gas is required to produce a very

high concentration in the milling

units, where most of the insects in

the modern mill are to be found.

Furthermore, by this method it is

unnecessary to dismantle and clean

out the machinery. It is estimated

that the saving in labor and shutdown time, together with the saving in fumigant required, will allow two fumigations for the same

cost as one by the open-space method. It is considered that enough

16
AMS Neg. U32li-^7(7)

Figure 6.—Method of piping machinery in a

flour mill for fumigation with liquid hydrocyanic acid. Mill house.

gas will escape from the machinery

to care for any insects that are in

the open space of the mill. In old

wooden mills the woodwork often

harbors large numbers of insects,

not all of which are reached by the

gas when it is applied by the machinery-piping system. For this

type of mill the open-space method

of fumigation would probably be

more satisfactory.

Additional Preparations

Before the mill is shut down the

preparations noted previously

should be followed; however, it is

not necessary to open up the machinery. In addition:

1. Loosen sifter doors (except Wolf

sifters) slightly to allow circulation of gas into all sifter sections.

2. Eemove accumulations of milling

stock behind feed gates or purifiers and either tie or block open

the feed gates to allow passage of

gas into slide spouts that carry

stock into the purifiers. Seal

purifier ventilator doors with

kraft paper.

3. Adjust dividing gates, or tips,

below the cant boards in reels and

purifiers so that they are vertical

or so that half will open one way

and half the other way. This is

essential in order that there may

be equal distribution of gas into

all the conveyors. Eemove stock

accumulations in reel and purifier-conveyor ends beyond reach

of the flights, as well as any

packed accumulations. Reel and

purifier-conveyor housing covers

should be kept closed.

4. Remove accumulations of stock

above the roll feed gate, clean

housings, block open the feeder

gates, and close all housing doors.

5. Raise hand levers of Buckley

grinders, thus compressing driving springs and separating

grinding surfaces to permit passage of gas through the mechanism.

6. Splitter valves on slide spouts

should be placed on center to

eliminate possibility of dead-air

spaces.

7. Before fumigation, apply air

pressure to the piping system and

examine each spray nozzle to see

that it is working properly.

Leaky connections should be

tightened. The care expended in

keeping the lines and nozzles

clear of deposits will be a big

factor in the success of fumigations by this method. Lines

should be blown clear of the

liquid fumigant after each fumigation.

17
Applying the Gas

When the liquid hydrocyanic acid

is introduced into the various milling units the gas must be forced

into the fumigation lines with sufficient pressure to ensure a uniform

distribution. As the standard hydrocyanic acid cylinder has too

small an aperture to allow this, it is

necessary to employ a special applicator consisting of a small steel tank

holding 35 pounds of the liquid and

capable of withstanding a working

pressure of 200 pounds. The gasoutlet valve on the top-central part

of the cylinder is connected with a

i/^-inch copper tube extending to the

bottom of the tank. This tube is

larger than that used in the hydrocyanic acid cylinder and permits the

gas to flow as rapidly as required.

Gas-inlet valves (%-inch brass) and

a pressure gage are also located on

the top-central part of the applicator. From the tank connection of

the gage a bypass of i^-inch copper

tubing, supplied with a valve, is

connected to the gas-outlet line between the gas-outlet valve and the

manifold of the piping system.

This bypass allows the pressure

created by the transfer of the hydrocyanic acid from the shipping cylinder to the applicator to escape into

the manifold, thus facilitating the

filling of the applicator.

Dosage Rate

Liquid hydrocyanic acid is forced

into the various lines at the rate of

about 8 ounces for each spray nozzle. Some fumigators prefer to use

a heavier dosage, but this is rarely

necessary.

At the end of the fumigation the

mill can be ventilated in the manner

employed in other fumigations.

Workmen wearing gas masks

should open all doors and windows

to allow air to circulate through the

building. Eoof vents should be

opened as soon as possible to allow

the gas to escape from the machinery.

To avoid accident from small

quantities of fumigant left in the

system, compressed air should be

forced through all fumigation lines

long enough to ensure a complete

removal of hydrocyanic acid. This

should be done during the ventilation process and before workmen

are allowed to enter the building.

Fumigation With Methyl Bromide

For the fumigation of modern,

tight, concrete, stone, or brick mills,

methyl bromide has been found

highly efficient. It is not recommended for use in mills of wood,

or of frame and sheet-metal construction, owing to the difficulty of

holding the vapors long enough to

obtain a satisfactory kill. A special technique, ordinarily too costly

to be employed, is required for making this type of building tight

enough for methy bromide fumigation.

Methyl bromide is a colorless almost odorless liquid that boils at

40.1° F. At ordinary room temperature itis a gas, in which state it

is more than 3 times heavier than

air. It is obtainable commercially

in liquid form in 1-pound cans or

in cylinders containing 50 or 175

pounds net. The natural pressure

of the gas is sufficient at room temperature so that both cans and cylinders are self-emptying when

opened. The pressure in the cylinders, however, is increased slightly

by the manufacturers to facilitate

the rapid removal of the gas.

Methyl bromide is relatively inexpensive at the dosages required

for fumigation, highly toxic to all

stages of insects including their

eggs, noninflammable at concentrations used in commercial practice,

and can be used successfully at

comparatively low temperatures.

18
It has remarkable powers of penetration and is undoubtedly the most

efficient fumigant known for the

treatment of warehouses filled with

bagged commodities. Lacking a

distinctive odor, this gas is but

faintly noticeable in small

amounts, a feature that creates a

hazard not present with some of

the rapidly toxic gases that possess distinctive warning properties.

Methyl bromide can be applied

through a piping system in much

the same manner as that described

for liquid hydrocyanic acid or by

releasing the gas directly into the

open space from cylinders placed

at strategic points in the mill.

Each cylinder of methyl bromide is

equipped with a siphon tube so that

it can be emptied without inverting

the cylinder.

If the gas is to be introduced into

a mill through a piping system, the

pressure in the cylinders should be

increased with compressed air to

150 pounds. The cylinder or cvlinders are then connected to the

manifold of the piping system on

the outside of the building. After

the valve is opened, the pressure

forces the fumigant from the cylinder into the fumigation lines at

the rate of about 10 pounds per minute. In cool weather the pressure

in the cylinder must sometimes be

built up with compressed air a second time to speed up the emptying

of the cylinder and the application

of the gas. A 3-way connection between the cylinder, the manifold,

and the air compressor will facilitate this operation. For large

mills, where this method of applying the gas is best adapted, the

175-pound cylinders will be most

convenient.

Small mills that do not have piping systems can be fumigated by

distributing the requisite number of

cylinders uniformly over the several

floors and releasing the gas by opening the valves (fig. 7). The 50-

Figure 7.—Applying methyl bromide in a flour mill.

19
pound cylinders will be found most

useful for the purpose and will

enable the fumigator to distribute

the gas uniformly over the building.

One-pound cans can be used to supplement the dosage and are particulary useful for treating small rooms

that are cut off from the regular mill

space. Each floor of the mill

should be provided with large portable fans, which should be operated

for at least 1 hour after the gas is

introduced, to ensure a proper distribution of the gas.

In applying the gas, the fumigator must be careful not to expose himself to the concentrated

vapors, and for his protection he

should be supplied with a gas

mask equipped with a black canister designed to protect against

organic vapors. If the gas is applied from the outside of the building it is not necessary to wear a gas

mask unless the manifold or cylinder connections are leaky, although

the mask should be kept handy for

use in case of emergency. Where

the cylinders are discharged directly into the open space of the

mill, the fumigator, starting from

the top of the mill, should proceed

from floor to floor, opening the

valves of the cylinders by hand and

discharging any 1-pound cans required. Two men wearing gas

masks should work together and

should release the gas as rapidly

as possible so that they will not

be exposed to a heavy concentration of the fumigant, which might

be hazardous even though they

are protected by masks.

A dosage of 1 pound per 1,000

cubic feet of space is adequate for

the fumigation of well-constructed

mills.

An exposure period of from 16 to

24 hours should be allowed, after

which the building may be opened

up for aeration. The same precaution should be taken in ventilating

the building as when hydrocyanic

acid or other toxic gas has been

used.

Workmen entering the building

to open the windows and doors

must wear gas masks equipped

with black canisters. Under ordinary conditions, a mill that has been

fumigated with methyl bromide

will air out rapidly after it is

opened up.

Fumigation With Chloropicrin

Chloropicrin has been used for

many years for the fumigation of

flour mills. It is nonexplosive and

nonflammable as ordinarily used for

fumigating purposes, and is extremely toxic to insects as well as

man.

Itis a colorless or slightly yellowish liquid a little more than one and

a half times as heavy as water. It

has a boiling point of 233.6° F. and

on exposure to air evaporates slowly

forming a mixture of gas and air

that is slightly heavier than air at

the same temperature and pressure.

Itis disagreeable to handle owing to

the lachrymatory properties of its

vapors; however, this can be considered as a safety factor since it is

improbable that anyone would willingly enter an atmosphere containing an appreciable quantity of

chloropicrin.

A full-face gas mask supplied

with a canister designed to

protect against organic vapors

should be worn while applying

the fumigant or in transferring

it from cylinders to vessels used

in dispensing it. Care should be

taken not to spatter the liquid on

the hands or feet or other areas

of the body since blistering of the

skin may result.

Chloropicrin is available in two

forms, with or without a propellant.

The propellant form is available in

50-pound containers of a 30-70 mix20
ture of methyl chloride and chloropicrin.

When the valve is opened the

methyl chloride propels the chloropicrin from the applicator in a fine

mist that vaporizes rapidly. A

plastic or copper tube extension can

be fitted to the outlet valve so as to

release the fumigant in the upper

part of each floor of the mill. Place

the container in Üie approximate

center of the space to be fumigated,

and adjust it so that there are no

obstacles (particularly belting)

within 12-15 feet of it in directions

in which the fumigant will be discharged. Cap and plug the end of

the extension tube leading from the

cylinder and bore a hole in each side

of the tube so thatthe fumigant will

be discharged horizontally in two

directions. In cold weather, store

the containers in a warm room for

at least 12 hours before they are

used. This will increase the pressure in them suiRciently to insure a

satisfactory discharge of the chloropicrin.

If condensation on the floor is expected, spread empty burlap sacks

on the floor 10 feet on each side of

the point of release.

The fumigators, wearing gas

masks, should open the valves one

full turn, and be careful to stand

so that they will not be sprayed

by the discharge. They should

work rapidly and leave the mill

as soon as possible.

In some cases a semi-permanent

piping system is installed of %-inch

o. d. polyethylene tubing. Copper

jets for discharging the gas are

spaced 20 to 30 feet apart. One jet

should be allowed for each 1,000

cubic feet of space, with not more

than 3 jets to a line. The jets are

rigid copper tubing 18 inches in

length connected to the polyethylene tubing with a brass tee. The

free end is pinched shut and is supplied with a i/ie-inch orifice drilled

through both walls 1 inch above the

pinched end.

Each floor of the mill or warehouse should be provided with one

or more lines fastened to the ceiling

and extending to the outside where

they can be connected to a cylinder

containing a mixture of chloropicrin and methyl chloride pressurized to 100 pounds. A dosage of

from 114 to 1% pounds of the mixture should be used per 1,000 cubic

feet of space depending upon the

quantities of machinery in the mill.

If the chloropicrin is used without a propellant, it can be sprinkled

on empty sacks spread on the floor

or poured on a pile of empty sacks.

A minimum of 1 pound of chloropicrin should be used per 1,000 cubic

feet of space. The required quantity of chloropicrin for each floor

should be distributed in handy containers before the fumigation.

After an exposure of 24 hours,

the mill should be thoroughly aerated before milling operations are

resumed.

Local Fumigation

The treatment of an individual

machine in a mill with a fumigant

is referred to as a local fumigation.

After a general fumigation to eliminate ^ the insect population of a

mill, it is only a matter of time before some of the milling units become reinfested from individual insects surviving the fumigation, or

through one or more of the avenues

by which insects enter the mill.

The proper use of local fumigants

will keep infestations at a point

where they will not be a serious factor. This is particularly true in

modern concrete mills where insects cannot find refuge in old woodwork. Some mills rely on periodic

local fumigations instead of an occasional general fumigation, but

insects that are established in the

woodwork will not be affected by

21
local fumigants and will continually reinfest the machinery. Local

fumigations can be conducted on

weekends or any night after the

mill is shut down. For best results they should be given every 2

or 3 weeks. Chloropicrin and mixtures containing carbon tetrachloride, ethylene dichloride, ethylene

dibromide, or methyl bromide are

used extensively for this purpose.

Dosages of three commonly used

formulations are given below as a

general guide. For the many other

formulations available, follow the

directions on the manufacturer's

label, but be sure to use a material

approved for this use.

Milling Unit

Elevator boots

Reels and purifiers

Sifters (each section)

Conveyors (per linear foot)

Rolls (each side)

Dusters

Bins (per 100 cu. ft.)

These dosages are general, and

individual mills and individual machines may require more or less

fumigant.

Prior to the application of local

fumigants, the mill should be run

until empty. However, the milling

stock should not be removed until

after the fumigation. All vents

from milling machinery to the outside should be closed. Dead spouts

and filled suction lines should be

cleaned.

The fumigants are applied by

workmen wearing full-face gas

masks equipped with proper canisters. Starting from the top floor

of the mill the liquid fumigants are

poured, sprayed or dashed into the

individual units. Care should be

taken to keep liquids off pobshed

metals such as rolls.

When chloropicrin is used, running the machinery for 2 or 3 minutes after application will aid in

the distribution of the vapors.

Some manufacturers of local fumigants provide automatic applicators that will measure and inject

the desired dose into each milling

Chloropicrin

Fluid ounces

8-10

16

2-3

}i

1

5-6

1

Ethylene

dichloride-carbon

tetraohloride

(3 :1)

Fluid ounces

12-16

16-20

12

2

8

16

10

Ethylene

dibromide

15 percent in a

chlorinated

solvent

Fluid ounces

12-16

16-20

12

2

8

16

10

unit through a small hole made for

this purpose.

The points of application will

vary in each mill and will have to

be determined by experience. In

some mills application to the elevator system has been found sufficient. The fumigant is applied at

three points—one in the head, and

one in each leg on the back side. In

most mills, sifters and some of the

milling units will require individual doses. By checking results in

each milling unit after a fumigation, one can soon discover which

unit will require individual doses.

The fumigant should be applied

to units on the lower floors first, the

operators working up towards the

top floor. This is the reverse of the

usual method of applying local fumigants. Since it is a machinery

fumigation the mill can be well ventilated during actual application of

the fumigant. This mixture is

also available in small cans containing just enough of the liquid to fumigate one unit. The contents of

a can are poured through a funnel

into the milling units through the

22
same holes used in treating with the

automatic applicator. This method

can be used when an applicator is

not available.

The mill should be thoroughly

aerated after fumigation and before milling operations are resumed.

Kesidual milling stock should be

removed from fumigated units with

a heavy-duty vacuum cleaner after

fumigation so that dead insects will

not add to the insect fragment count

in the finished flour. This operation can be completed before the

mill is restarted, or on the following weekend.

Heat and Cold for Treating Flour Mills

The effectiveness of heat in the

control of insects infesting flour

mills has been known for several

decades. The cost of superheating

mills compares favorably with that

of fumigation ; however, the length

of exposure required and the deleterious effect of high temperature

on some milling equipment has resulted in the abandonment of this

method by all but a few mills.

Where it is still employed, air

drawn over the steam coils of unit

heaters is blown through the mill.

This method is superior to the old

method which relied on radiation

from steam pipes. To be successful, temperatures of from 120° to

130° F. must be maintained for

from 10 to 12 hours.

The opening up of mills during

a period of subzero weather to kill

insects by freezing has been a practice used occasionally in the Northern States and in the Prairie Provinces of Canada. It is not widely

practiced in the United States owing to the uncertainty of the weather. During the exposure period it

is necessary to drain all water pipes

to prevent damage from freezing.

Continuous-Process Heat Treatment of Milled

Cereal Products

Milled cereal products too coarse

to permit sieving to remove any insect life that might later start an

infestation must be given some precautionary treatment to gain this

end. Continuous-process sterilization by heat has been found most

satisfactory and economical and is

more commonly used than any other

treatment.

Many concerns heat their product

to temperatures of 160° F. or

higher. The important point is to

make certain that the product is

uniformly heated. The maximum

temperature that can be employed

will depend on the product and use

for which it is intended. Flours to

be used for raised bread or pastry

cannot be subjected to temperatures

above 170° with safety. Cereal

products, however, can stand much

higher temperatures. Insects that

might be found in milled cereal

products can not survive exposure

to a temperature of 140° for more

than 5 minutes; hence, raising the

temperature of the product to 140°

or slightly higher and maintaining

it at that level for about 10 minutes

will produce satisfactory sterilization.

Figure 8 illustrates a procedure

for heating and cooling a cereal

product that, according to Chapman,^ is highly satisfactory.

A number of machines on the

market have been designed for heattreating milled cereal products, the

heat being derived from steam, hot

air, or electricity. In many, pro-

^ Chapman, R. N. Insects infesting

stored food products. Minn. Agr. Expt.

Sta. Bui. 198, 76 pp., illus. 1921.

23
Tançeratùre

200"F,

190

180

170

160

150

lll-O

130

120

110

100

80

Figure

A^^^"^—^-^--iïi^ff f

\

¿s

i V■■""■♦-*••••.

1 Teaçeratur© Fatal to Inaecte *^" .^^

Time In Minutes

10 11 12 13 AMS Neg. 1*325-57(7)

8.—A satîsfacfory temperoture range for cereals during the process of heating and

packing. (Chapman.)

vision is also made to prevent loss

in moisture content of the product

during the treatment. To be satisfactory for the purpose, a machine

should heat the product uniformly.

Heat-sterilized cereal products

should go directly from the sterilizer to the packer to prevent reinfestation before packing. A sterilizer of simple construction consists

of a series of steam-jacketed metal

cylinders or drums placed horizontally one above another and connected so that corn meal, farina, or

any other milled cereal product

introduced into one end of the top

cylinder is conveyed to the other end

of the cylinder by a screw conveyor,

where it drops into the cylindCéT below. The cereal product is conveyed in a similar manner through

the entire series of cylinders. In its

passage through the various cylinders the product will be gradually

and uniformly heated, until it

emerges atthe bottom at any desired

temperature. With a series of three

cylinders operating at a steam

pressure of 100 pounds, the temperature of a cereal product can be

raised to 160° F. in 5 to 6 minutes.

The heated product should then be

sifted through a 20-mesh screen to

remove any material that may have

been caked by the heat, and should

be packed while still hot. Different

combinations of heating cylinders

and steam pressures can be used to

suit individual situations.

Insect Contamination in Milled Cereal Products

Flour shipments used in blending

operations, in mixes, or specialty

products, or by bakers, should always be examined for both insect

infestation and insect contamination. The presence of living infestation can be determined by sifting.

At least 1 percent of the bags taken

at random from each carload of

flour should be sifted.

For the detection of insect fragments in milled cereals, which may

be present but are not detectable

by macroscopic examinations, pro24
cedures have been published by the

Food and Drug Administration,

The Association of Official Agricultural Chemists, and the American

Association of Cereal Chemists.

Recommendations relative to useful procedures for the examination

of food products for extraneous materials that will also be found helpful to analysts are contained in the

Eeport of the 1945-46 Committee

of the New York Section of the

American Association of Cereal

Chemists. Essentially, the process

consists of digesting the sample

with pancreatin or hydrochloric

acid, making gasoline or light mineral oil separations of the extraneous material, and identifying the

separated material.

A method for detecting insect excreta in flour has also been published in "Methods of Analysis" of

the Association of Official Agricultural Chemists (5th ed., p. 715).

Insect Control in the Warehouse

Sanitation and Warehouse

Management

Under modern methods of flour

manufacturing, freshly milled flour

stocks can be considered free of insect infestation when they enter the

warehouse. However, in flour

warehouses every precaution should

be taken to prevent the development of insect infestation in stocks

awaiting shipment. Sources of infestation include the following : Infested accumulations of dust, feed,

and flour in difficult-to-reach places,

such as between double floors, walls,

and partitions, and in unused machinery or bins; crpss infestation

from infested feeds, old stock,

broken bags or returned goods ; and

invasion from nearby elevators.

Many warehouses are of modern

construction and can easily be kept

clean and sanitary. If necessary,

warehouse construction should be

improved, double hollow walls and

partitions eliminated, and cracks in

floors filled or the floor renovated

by laying quick-setting plastic

preparations over old ones. Foodhandling equipment and all machinery or dunnage likely to harbor insects should be removed unless it is in constant use.

Flour should be stored in rooms

separate from feeds. It should

also be stacked on pallets of suitable size, in piles at least 12 inches

from the walls and far enough

apart to allow inspection and cleaning. Pallets should be inspected

regularly for infestation, cleaned

with compressed air, and the undersides sprayed with a residual spray.

Information regarding sprays described for use in the mill will apply equally well for the warehouse.

Stocks of flour longest in storage

should be moved first as the sales

demand. Broken bags should be

disposed of immediately. Floors

should be regularly swept and all

accumulations removed and burned

or fumigated. Whenever a pile of

flour is shipped, the floor beneath

it should be thoroughly cleaned.

The use of a heavy duty vacuum

cleaner will be found invaluable.

Mechanical sweepers with attached

vacuum have been found to be efficient and economical.

Fumigation

The fumigation of flour and feed

warehouses is frequently practiced

in connection with mill fumigations. Observations indicate that

in tight concrete or brick warehouses hydrocyanic acid, chloropicrin, methyl bromide, or mixtures

of methyl bromide with ethylene

dibromide can be used at the same

dosage recommended for mill fumigation. Fumigation must be re25
stricted to empty warehouses since

no tolerances have been established

for residues in manufactured foods

resulting from fumigations.

Bulk Flour Storage

Where there is a bulk flour system

care must be taken to prevent the

buildup of insect infestation in the

flour-handling equipment as well as

in the bins. In addition to frequent

cleaning of conveyors, elevators,

and all other parts of the system, a

centrifugal machine should be used

to give the flour just ahead of the

handling equipment a precautionary treatment.

Flour going from bulk storage to

packers or to bulk cars or trucks

should be rebolted and treated

with a centrifugal machine as a

precautionary treatment to remove

insect life that might later start an

infestation.

The type of storage bin is of considerable importance. Riveted

metal bins are most desirable, concrete bins next best, and wooden

bins least desirable. Metal bins, if

welded, often crack at the joint due

to stress and strain. Riveted seams

should be calked with an inert plastic capable of retaining its resilience

for several years.

Insect-Resistant Bags

Unless flour is properly packaged

and protected from insect invasion

in storage and transit, much of the

effort expended in the manufacture

of a clean product may be wasted.

Insects that attack flour are found

wherever foodstuffs are stored or

merchandised, and are frequently

found infesting transportation facilities.

A mechanical barrier is the best

protection against invasion by insects. Fabric bags afford little protection from insect attack since the

insects can penetrate or lay their

eggs through the mesh of the fabric

or through needle holes along the

seams or end closures. Paper bags

have largely replaced fabric bags

and offer considerable protection to

flour from insect invasion if they

are properly made and sealed.

With the exception of the cadelle

and the lesser grain borer, most

flour-infesting insects cannot cut

through the walls of substantial

paper bags. They can and do, however, enter through needle holes

where the bags are sewed unless the

holes are protected in some way.

All seams of paper bags should be

cemented, and sewed tops should be

protected with strips of gummed

tape or other covering.

The use of an insect repellant

impregnated in the outer wall of

multiwalled paper bags offers excellent protection against insect

invasion for many months. A combination of pyrethrins with a Synergist, piperonyl butoxide, has been

used successfully as a repellent, and

bags so treated are now available

commercially. They are somewhat

more expensive than untreated bags.

For specialty flours or pre-mixes

a tight-wrap carton offers the most

satisfactory protection against insect infestation.

Infestation in Transit

Flour products leaving the mill to bakeries, other warehouses,^ or

or warehouse do not usually go di- grocery stores for distribution,

rectly to the consumer, but must be During this period of transit they

transported by truck or railway car are subject to invasion by insects.

26
Studies have shown that the railway cars used to transport flour

have in many cases also been used

to carry gram during the rush of

the grain-harvesting season. The

ordinary car is so constructed that

waste grain, grain dust, or milled

cereal products become lodged in

cracks and crevices in the woodwork and behind linings. Consequently, insect infestations difficult

to eradicate by ordinary clean-up

methods become established in cars

used to carry grain. As soon as

fresh flour is placed in infested cars,

the insects are attracted to it. They

crawl over the bags, thrust eggs

through the mesh of fabric bags,

and enter them wherever they can.

The time of greatest danger from

infestation in transit is during the

summer after the cars have been

used for carrying grain or feed. At

this time, also, large numbers of

insects of many kinds, including

species that infest grain and flour,

are in flight and enter the cars before or during loading operations.

Lights used in loading cars may

also attract many insects and, although they may not be important

pests of stored flour, their presence

is annoying and often causes cars

to be rejected on arrival at destination.

One of the best ways to prevent

the establishment of waste grain

and niilled products behind car linings is to install pads or blankets

of fiber glass behind end and side

linings. This material is resilient.

and when compressed tightly behind wooden linings fills the void to

the exclusion of any other material.

Many railroads have equipped test

cars with fiber-glass pads in the end

linings and have demonstrated the

value of this treatment.

It will probably be many years

before more than a token number

of such cars are available for flour

shipments. Until that time the

following procedures for treating

railway boxcars to be used for flour

shipments are recommended : Thoroughly sweep cars, and blow them

out with a jet of compressed air.

Spray with a residual-type spray

at least 12 hours before papering

and loading.

Sprays of DDT, TDE, methoxychlor, pyrethrum, or allethrin are

safe to use. The first 3 chemicals

should be used at a concentration

of 2.5 percent in the form of emulsions or wettable powders, and the

last two at a concentration of 0.5

percent as emulsions. They should

all be applied at the rate of about 1

gallon per 1,000 square feet of surface area. A power sprayer is desirable for speed in application and

to obtain good coverage. The absence of odor from the spray used

is essential. In general, water

emulsion sprays are less likely to

leave odors than other forms.

Sprayed cars should be lined with

a heavy kraft paper to a height

above the load. This lining will

protect the flour from spray deposits on the floor or walls of the car.

Bulk Transportation of Flour

Bulk transportation of flour offers fewer opportunities for insect

contamination than previously used

transport, provided the seller and

buyer accept their fair share of responsibility for the inspection and

care of equipment.

Bulk shipments of flour are presumably free from infestation if

handled according to the recommendations given for bulk flour storage.

The sanitary condition of bulk

flour cars, tote bins, and bulk flour

containers is essential. The shipper

must inspect all such equipment before loading. If inspection shows

infestation or some residue of previous loadings, steps must be taken

27
to put the car in acceptable condition for loading.

Upon receipt of the bulk commodity by the buyer and after unloading, the empty container must

be inspected. The receiver of the

commodity should assume the responsibility for complete unloading

(leaving no residue) and the immediate closing, locking, and sealing of loading hatches and unloading ports.

Electromagnetic Energy

The use of radiant energy for the

treatment of grain and cereal products has received considerable attention during the past few years.

Eadiant energy includes electrical

energy of various wave lengths,

such as radio, infrared, gamma

rays, sound waves, and energy from

electrons.

Many workers have demonstrated

that insects can be killed with radiant energy ; however, at present, the

high cost of equipment, upkeep and

operation, together with limitations

in capacity, make it doubtful

whether radiant energy can compete

with other methods of insect control now in use. Continued research

may result in the development of a

practical method of using some

form of radiant energy for treating

grain and cereal products.

o

28