Chapter 7: Scombrotoxin (Histamine) Formation (A Chemical …

 

 

Chapter 7: Scombrotoxin (Histamine) Formation (A Chemical Hazard)

Hazard Analysis Worksheet

STEP #10: UNDERSTAND THE POTENTIAL
HAZARD.

Scombrotoxin formation as a result of time/tempera-
ture abuse of certain species of fish can cause con-
sumer illness. The illness is most closely linked to
the development of histamine in these fish. In most
cases histamine levels in illness-causing fish have
been above 200 ppm, often above 500 ppm. How-
ever, there is some evidence that other chemicals
(e.g. biogenic amines, such as putrescine and cadav-
erine) may also play a role in the illness. The
possible role of these chemicals in consumer illness
is discussed in Chapter 8.

Scombroid poisonings have primarily been associ-
ated with the consumption of tuna, mahi mahi, and
bluefish. However, Table #3-1 (Chapter 3) lists a
number of species that are also capable of developing
elevated levels of histamine when temperature
abused.

• Scombrotoxin formation

Certain bacteria produce the enzyme histidine
decarboxylase during growth. This enzyme reacts
with free histidine, a naturally occurring chemical
that is present in larger quantities in some fish than in
others. The result is the formation of histamine.

Histamine-forming bacteria are capable of growing
and producing histamine over a wide temperature
range. Growth is more rapid, however, at high-abuse
temperatures (e.g. 70˚F [21.1˚C]) than at moderate-
abuse temperatures (e.g. 45˚F [7.2˚C]). Growth is
particularly rapid at temperatures near 90˚F (32.2˚C).
Histamine is more commonly the result of high
temperature spoilage than of long term, relatively low
temperature spoilage. Nonetheless, there are a
number of opportunities for histamine to form under
more moderate abuse temperature conditions.

Once the enzyme histidine decarboxylase has been
formed, it can continue to produce histamine in the
fish even if the bacteria are not active. The enzyme
can be active at or near refrigeration temperatures.
The enzyme is likely to remain stable while in the
frozen state and may be reactivated very rapidly after
thawing.

Freezing may inactivate the enzyme-forming bacteria.
Both the enzyme and the bacteria can be inactivated
by cooking. However, once histamine is formed, it
cannot be eliminated by heat (including retorting) or
freezing. After cooking, recontamination of the fish
with the enzyme-forming bacteria is necessary for
additional histamine to form. For these reasons,
histamine development is more likely in raw, unfro-
zen fish.

The kinds of bacteria that are associated with hista-
mine development are commonly present in the salt
water environment. They naturally exist on the gills
and in the gut of live, salt water fish, with no harm to
the fish. Upon death, the defense mechanisms of the
fish no longer inhibit bacterial growth, and histamine-
forming bacteria start to grow and produce histamine.
Evisceration and removal of the gills in a sanitary
manner may reduce, but not eliminate, the number of
histamine-forming bacteria. However, when done
under insanitary conditions, these steps may acceler-
ate the process of histamine development in the edible
portions of the fish by spreading the bacteria to the
flesh of the fish.

With some harvesting practices, such as long lining,
death can occur before the fish is removed from the
water. Under the worst conditions histamine forma-
tion can already be underway before the fish is landed
on the vessel. This condition can be aggravated when
the fish is allowed to remain on the line for a period
of time after death, a situation that in certain tuna
species may cause its internal temperature to increase
to a more favorable growth range for the enzyme-
forming bacteria.

Chapter 7: Histamine
83

Continued

The potential for histamine formation is increased
when the flesh of the fish is directly exposed to the
enzyme-forming bacteria. This occurs when the fish
are processed (e.g. butchering or filleting).

At least some of the histamine-forming bacteria are
halotolerant (salt-tolerant) or halophilic (salt-loving).
This causes some salted and smoked fish products
produced from scombrotoxin-forming species to
continue to be suspect for histamine development.
Further, a number of the histamine-forming bacteria
are facultative anaerobes that can grow in reduced
oxygen environments.

• Controlling scombrotoxin formation

Rapid chilling of fish immediately after death is the
most important element in any strategy for preventing
the formation of scombrotoxin, especially for fish
that are exposed to warmer waters or air, and for
large tuna that generate heat in the tissues of the fish
following death. It is recommended that:

• Generally, fish should be placed in ice or in

refrigerated seawater or brine at 40˚F (4.4˚C) or
less within 12 hours of death, or placed in
refrigerated seawater or brine at 50˚F (10˚C) or less
within 9 hours of death;

• Fish exposed to air or water temperatures above
83˚F (28.3˚C), or large tuna (i.e., above 20 lbs.)
that are eviscerated before on-board chilling, should
be placed in ice (including packing the belly

cavity of large tuna with ice) or in refrigerated
seawater or brine at 40˚F (4.4˚C) or less within 6
hours of death;

• Large tuna (i.e., above 20 lbs.) that are not

eviscerated before on-board chilling should be
chilled to an internal temperature of 50˚F (10˚C) or
less within 6 hours of death.

This will prevent the rapid formation of the enzyme
histidine decarboxylase. Once this enzyme is formed,
control of the hazard is unlikely.

Further chilling towards the freezing point is also
desirable to safe-guard against longer-term, low-
temperature development of histamine. Additionally,
the shelf-life of the fish is significantly compromised
when product temperature is not rapidly dropped to
near freezing.

The time required to lower the internal temperature
of fish after capture will be dependent upon a number
of factors, including:

• The harvest method;

– Delays in removing fish from a long line may
significantly limit the amount of time left for
chilling and may allow some fish to heat up after
death;

– The quantity of fish landed in a purse seine or on

a long line may exceed a vessel’s ability to
rapidly chill the product;

• The size of the fish;
• The chilling method;

– Ice alone takes longer to chill fish than does an ice
slurry or recirculated refrigerated sea water or
brine, a consequence of reduced contact area and
heat transfer;

– The quantity of ice or ice slurry and the capacity
of refrigerated sea water or brine systems must
be suitable for the quantity of catch.

Once chilled, the fish should be maintained as close
as possible to the freezing point (or held frozen) until
it is consumed. Exposure to ambient temperature
should be minimized. The allowable exposure time is
dependent primarily upon the speed with which the
fish were chilled on-board the harvest vessel and
whether the fish has been previously frozen (e.g. on-
board the harvest vessel).

Unfrozen scombrotoxin-forming fish has a safe shelf-
life (days before elevated levels of histamine are
formed) that is dependent upon the harvest methods,
the on-board handling, and the time/temperature
exposures throughout processing, transit, and storage.
This safe shelf-life can be as little as 5 to 7 days for
product stored at 40˚F (4.4˚C).

Any exposure time above 40˚F (4.4˚C) significantly
reduces the expected safe shelf-life. For this reason,
fish that have not been previously frozen should not
be exposed to temperatures above 40˚F (4.4C) for
more than 4 hours, cumulatively, if any portion of that
time is at temperatures above 70˚F (21˚C); or the fish
should not be exposed to ambient temperatures above
40˚F (4.4˚C) for more than 8 hours, cumulatively, as
long as no portion of that time is at tempera

Chapter 7: Histamine
84

tures above 70˚F (21˚C) after chilling on board the
harvest vessel. The safety of these limits is dependent
upon proper handling at sea.

Fish that have been previously frozen can safely
withstand considerably more exposure to elevated
temperatures during post-harvest handling. Such fish
should not be exposed to temperatures above 40˚F
(4.4C) for more than 12 hours, cumulatively, if any
portion of that time is at temperatures above 70˚F
(21˚C); or the fish should not be exposed to ambient
temperatures above 40˚F (4.4˚C) for more than 24
hours, cumulatively, as long as no portion of that time
is at temperatures above 70˚F (21˚C), after chilling on
board the harvest vessel. The safety of these limits is
again dependent upon proper handling at sea.

Extended frozen storage (e.g. 24 weeks) or cooking
minimizes the risk of additional histamine develop-
ment by inactivating the enzyme-forming bacteria
and, in the case of cooking, the enzyme itself. As
previously mentioned, recontamination with enzyme-
forming bacteria and significant temperature abuse is
necessary for histamine formation under these
conditions. Such recontamination may not be likely
if the fish is processed under a conscientious sanita-
tion program.

• Detection

Sensory evaluation is generally used to screen fish
for spoilage odors that develop when the fish is
exposed to time/temperature abuse. It is an effective
means of detecting fish that have been subjected to a
variety of abusive conditions.

However, odors of decomposition that are typical of
relatively low temperature spoilage may not be
present if the fish has undergone high temperature
spoilage. This condition makes sensory examination
alone an ineffective control for scombrotoxin.

Chemical testing is an effective means of detecting
the presence of histamine in fish flesh. However, the
validity of such testing is dependent upon the design
of the sampling plan. The amount of sampling
required to accommodate such variability is necessar-
ily quite large. For this reason, chemical testing

alone will not normally provide adequate assurance
that the hazard has been controlled. Because hista-
mine is generally not uniformly distributed in a
decomposed fish, a guidance level of 50 ppm has
been set. If 50 ppm is found in one section, there is
the possibility that other sections may exceed 500 ppm.

Observations for the presence of honeycombing in
precooked tuna loins intended for canning is also a
valuable means of screening for fish that have been
exposed to the kinds of temperature abuse that can
lead to histamine development. Any fish that demon-
strate the trait should be destroyed.

STEP #11: DETERMINE IF THIS
POTENTIAL HAZARD IS SIGNIFICANT.

At each processing step, determine whether
“scombrotoxin formation” is a significant hazard.
The criteria are:

1. Is it reasonably likely that unsafe levels of histamine
will be introduced at this processing step (do unsafe
levels come in with the raw material)?

Table #3-1 (Chapter 3) lists those species of fish that
are generally known to be capable of producing
elevated levels of histamine if temperature abused.
This is because they contain naturally high levels of
free histidine. It is also because they are marine fish
that are likely to harbor the kinds of bacteria that
produce histidine decarboxylase. It is, therefore,
reasonable to assume that, without proper on-board
controls, these species of fish will contain unsafe
levels of histamine upon receipt by the primary (first)
processor.

However, if the worst case environmental conditions
(i.e. air and water temperatures) during the harvest
season in a particular region would not permit the
formation of histamine during the time necessary to
harvest and transport the fish to the primary proces-
sor, on-board controls may not be necessary. For
example, such conditions might exist if the fish are
harvested when air and water temperatures do not
exceed 40˚F (4.4˚C), or when the combination of air
and water temperature and harvest/transport time are
such that histamine formation is not reasonably likely
to occur, as documented by a scientific study.

Chapter 7: Histamine
85

Continued

It is also reasonable to assume that, without proper
controls during refrigerated (not frozen) transporta-
tion between processors, scombrotoxin-forming
species of fish will contain unsafe levels of histamine
upon receipt by the secondary processor (including
warehouses). However, this may not be the case if
the product being received is a cooked or frozen fish
or fishery product.

Nevertheless, you may need to exercise control when
receiving a refrigerated (not frozen) product from
another processor to prevent pathogen growth or
toxin formation (see Chapter 12).

2. Is it reasonably likely that unsafe levels of histamine
will form at this processing step?

To answer this question you should consider the
potential for time/temperature abuse in the absence of
controls. You may already have controls in your
process that minimize the potential for time/tempera-
ture abuse that could result in unsafe levels of
histamine. This and the following steps will help you
determine whether those or other controls should be
included in your HACCP plan.

Time/temperature abuse that occurs at successive
processing and storage steps may be sufficient to
result in unsafe levels of histamine, even when abuse
at one step alone would not result in such levels. For
this reason, you should consider the cumulative effect
of time/temperature abuse during the entire process.
Information is provided in Step #10 to help you
assess the significance of time/temperature abuse that
may occur in your process.

3. Can the formation of unsafe levels of histamine that
are reasonably likely to occur be eliminated or reduced
to an acceptable level at this processing step? (Note:
If you are not certain of the answer to this question at
this time, you may answer “No.” However, you may
need to change this answer when you assign critical
control points in Step #12.)

“Scombrotoxin formation” should also be considered
a significant hazard at any processing or storage step
where a preventive measure is or can be used to
eliminate the hazard, if it is reasonably likely to
occur. Preventive measures for “scombrotoxin
formation” can include:

• Making sure through harvest vessel records that

incoming fish were properly handled on-board the
harvest vessel, including:
– Rapidly chilling the fish immediately after death;
– Controlling on-board refrigeration (other than

frozen storage) temperatures;

– Proper on-board icing;

• Testing incoming fish for histamine levels;
• Making sure that incoming fish were handled

properly during refrigerated transportation from
the previous processor, including:
– Controlling refrigeration temperatures during transit;
– Proper icing during transit;

• Checking incoming fish to ensure that they are

not at an elevated temperature at time of receipt;

• Checking incoming fish to ensure that they are
properly iced or refrigerated at time of receipt;
• Performing sensory examination on incoming fish

to ensure that they do not show signs of decom
position;

• Controlling refrigeration temperatures in your plant;
• Proper icing in your plant;
• Controlling the amount of time that the product
is exposed to temperatures that would permit
histamine formation during processing and storage.

List such preventive measures in Column 5 of the
Hazard Analysis Worksheet at the appropriate
processing step(s).

If the answer to either question 1, 2 or 3 is “Yes” the
potential hazard is significant at that step in the
process and you should answer “Yes” in Column 3 of
the Hazard Analysis Worksheet. If none of the
criteria is met you should answer “No.” You should
record the reason for your “Yes” or “No” answer in
Column 4. You need not complete Steps #12 through
18 for this hazard for those processing steps where
you have recorded a “No.”

It is important to note that identifying this hazard as
significant at a processing step does not mean that it
must be controlled at that processing step. The next
step will help you determine where in the process the
critical control point is located.

Chapter 7: Histamine
86

• Intended use

In determining whether a hazard is significant you
should also consider the intended use of the product,
which you developed in Step #4. However, because
of the stable nature of histamine, the intended use of
the product is not likely to affect the significance of
this hazard.

STEP #12: IDENTIFY THE CRITICAL
CONTROL POINTS (CCP).

For each processing step where “scombrotoxin
formation” is identified in Column 3 of the Hazard
Analysis Worksheet as a significant hazard, deter-
mine whether it is necessary to exercise control at
that step in order to control the hazard. Figure #A-2
(Appendix 3) is a CCP decision tree that can be used
to aid you in your determination.

The following guidance will also assist you in
determining whether a processing step is a CCP for
scombrotoxin formation:

1. If you identified scombrotoxin formation as a
significant hazard at the receiving step in Step #11,
you should also identify receiving as a CCP for this
hazard. Preventive measures, such as the first six
described in Step #11, should be available to you at
that step.

In this case you should enter “Yes” in Column 6 of
the Hazard Analysis Worksheet for the receiving step.
A control approach which includes screening incom-
ing fish through harvest vessel records for on-board
handling practices will be referred to as “Control
Strategy Example 1” in Steps #14-18. A control
approach which includes screening incoming fish
through histamine testing will be referred to as
“Control Strategy Example 2” in Steps #14-18. A
control approach which includes screening incoming
fish to ensure proper handling during transit from the
previous processor will be referred to as “Control
Strategy Example 3” in Steps #14-18.

2. If you identified scombrotoxin formation as a
significant hazard at a processing or storage step in
Step #11, it may be necessary for you to also identify
that processing step as a CCP for this hazard. Preven-
tive measures, such as the last three described in Step
#11, should be available to you at those steps.

Example:
A fresh mahi mahi processor identifies a series of
processing and storage steps (e.g. butchering,
packaging, and refrigerated storage) as presenting a
reasonable likelihood of scombrotoxin formation.
The processor controls temperature during storage
and time of exposure to unrefrigerated conditions
during the processing steps. The processor identifies
each of these processing and storage steps as CCPs
for this hazard.

In this case, you should enter “Yes” in Column 6 of
the Hazard Analysis Worksheet for each of those
processing steps. This control approach will be
referred to as “Control Strategy Example 1, 2 and 3”
in Steps #14-18. It may apply to any of the three
previously described control strategies.

It is important to note that you may select a control
strategy that is different from that which is suggested
above, provided that it assures an equivalent degree
of safety of the product.

• Likely CCPs

Following is further guidance on processing steps
that are likely to be identified as critical control
points for this hazard:
• Receiving;
• Processing, such as:

– Thawing;
– Brining;
– Heading and gutting;
– Manual filleting and steaking;
– Stuffing;
– Mixing;
– Portioning;

• Packaging;
• Final chilling after processing and packaging;
• Raw material, in-process product, and finished

product refrigerated storage.

(Note: Rather than identify each processing step as
an individual CCP when the controls are the same at
those steps, it may be more convenient to combine
into one CCP those processing steps that together
contribute to a cumulative time/temperature exposure.)

Chapter 7: Histamine
87

Continued

• Unlikely CCPs

Time/temperature controls will usually not be needed
at processing steps that meet the following condi-
tions:
• Continuous, mechanical processing steps that are

brief, such as:
– Mechanical filleting;

• Processing steps that are brief and unlikely to
contribute significantly to the cumulative time/
temperature exposure, such as:
– Date code stamping;
– Case packing;

• Processing steps where the product is held in a

frozen state, such as:
– Assembly of orders for distribution;
– Frozen product storage;

• Retorting and post-retorting steps (if the product is
covered by the LACF regulations, 21 CFR 113);

• Canned tuna “precooking” and steps after pre-
cooking, if sanitation practices are sufficient
to prevent recontamination with enzyme-forming
bacteria.

Proceed to Step #13 (Chapter 2) or to Step #10 of the
next potential hazard.

HACCP Plan Form

STEP #14: SET THE CRITICAL LIMITS (CL).

For each processing step where “scombrotoxin
formation” is identified as a significant hazard on the
HACCP Plan Form, identify the maximum or mini-
mum value to which a feature of the process must be
controlled in order to control the hazard.

You should set the CL at the point that if not met the
safety of the product may be questionable. If you set
a more restrictive CL you could, as a result, be
required to take corrective action when no safety
concern actually exists. On the other hand, if you set
a CL that is too loose you could, as a result, allow
unsafe product to reach the consumer.

As a practical matter it may be advisable to set an
operating limit that is more restrictive than the CL.
In this way you can adjust the process when the
operating limit is triggered, but before a triggering of
the CL would require you to take corrective action.
You should set operating limits based on your experi-
ence with the variability of your operation and with
the closeness of typical operating values to the CL.

Following is guidance on setting critical limits for the
control strategy examples discussed in Step #12.

• CONTROL STRATEGY EXAMPLE 1 –

HARVEST VESSEL CONTROL

For receipt by primary (first) processor:

Critical Limit: All lots received are accompanied by

harvest vessel records that show:
• Generally, the fish were:

– Placed in ice, or in refrigerated seawater or

brine at 40˚F (4.4˚C) or less, within 12 hours
of death;
OR

– Placed in refrigerated seawater or brine at
50˚F (10˚C) or less within 9 hours of death
and chilling continued to bring the internal
temperature of the fish to 40˚F (4.4˚C) or less;

OR
• Fish exposed to air or water temperatures
above 83˚F (28.3˚C), ), or large tuna (i.e.,
above 20 lbs.) that are eviscerated before
on-board chilling, should be placed in ice
(including packing the belly cavity of large
tuna with ice) or in refrigerated seawater or
brine at 40˚F (4.4˚C) or less within 6 hours of
death;

OR
• Large tuna (i.e., above 20 lbs.) that are not
eviscerated before on-board chilling: The
internal temperature of the fish was brought to
50˚F (10˚C) or less within 6 hours of death
and chilling continued to bring the internal
temperature of the fish to 40˚F (4.4˚C) or less;

Chapter 7: Histamine
88

OR
• Other critical limits for on-board handling

• CONTROL STRATEGY EXAMPLE 2 –

HISTAMINE TESTING

AND

AND

(e.g. maximum refrigerated brine or seawater
temperature, maximum fish size, maximum
fish to brine/seawater/ice ratio, maximum
ambient temperature exposure time before
chilling) necessary to achieve a cooling rate
that will prevent development of histamine in
the specific species, as established through a
scientific study;

AND
• For fish held refrigerated (not frozen) on-board
the vessel: The fish were stored at or below
40˚F (4.4˚C) thereafter;

• Sensory examination of a representative
sample of fish shows no more than 2.5%
decomposition (persistent and readily
perceptible) in the sample. For example, no
more than 3 fish in a sample of 118 fish may
show signs of decomposition;

• For fish held iced or refrigerated (not frozen)
on-board the vessel and delivered 24 or more
hours after death: The internal temperature
should be 40˚F (4.4˚C) or below;

OR
• For fish held iced or refrigerated (not frozen)
on-board the vessel and delivered from 12 to
less than 24 hours after death: The internal
temperature should be 50˚F (10˚C) or below;

OR
• For fish held iced or refrigerated (not frozen)
on-board the vessel and delivered in less than
12 hours after death: The internal temperature
should demonstrate that appropriate chilling
methods were used onboard the harvest vessel.
Chilling of the fish must begin on the harvest
vessel regardless of the time from death to
delivery, unless the environmental conditions
(e.g. air and water temperatures) are
consistently below 40˚F (4.4˚C) from the time
of death to delivery.

For receipt by primary (first) processor:

Critical Limit: Analysis of a representative sample of
fish shows less than 50 ppm histamine in all
fish in the sample;

AND

AND

• Sensory examination of a representative
sample of fish shows no more than 2.5%
decomposition (persistent and readily
perceptible) in the sample. For example, no
more than 3 fish in a sample of 118 fish may
show signs of decomposition;

• For fish held iced or refrigerated (not frozen)
on-board the vessel and delivered 24 or more
hours after death: The internal temperature
should be 40˚F (4.4˚C) or below;

OR
• For fish held iced or refrigerated (not frozen)
on-board the vessel and delivered from 12 to
less than 24 hours after death: The internal
temperature should be 50˚F (10˚C) or below;

OR
• For fish held iced or refrigerated (not frozen)
on-board the vessel and delivered in less than
12 hours after death: The internal temperature
should demonstrate that appropriate chilling
methods were used onboard the harvest vessel.
Chilling of the fish must begin on the harvest
vessel regardless of the time from death to
delivery, unless the environmental conditions
(e.g. air and water temperatures) are
consistently below 40˚F (4.4˚C) from the time
of death to delivery.

Chapter 7: Histamine
89

Continued

• CONTROL STRATEGY EXAMPLE 3 –

TRANSIT CONTROL

For receipt by secondary processor (including
warehouse):

Critical Limit: For fish delivered refrigerated (not

frozen): All lots received are accompanied by

transportation records that show that the fish

were held at or below 40˚F (4.4˚C) throughout
transit;
OR
For fish held under ice or chemical cooling
media: There is an adequate quantity of ice or
other cooling media at the time of delivery to
completely surround the product.

• CONTROL STRATEGY EXAMPLE 1, 2 & 3

For processing steps:

Critical Limit: During processing and refrigerated (not
frozen) storage that occurs before cooking (e.g.
canned tuna “precook”): For fish that have not been
previously frozen:

• The fish are not exposed to ambient

temperatures above 40˚F (4.4˚C) for more than
4 hours, cumulatively, if any portion of that

time is at temperatures above 70˚F (21˚C);
OR
• The fish are not exposed to ambient

temperatures above 40˚F (4.4˚C) for more than
8 hours, cumulatively, as long as no portion of
that time is at temperatures above 70˚F (21˚C);

(Note: Only one of the above two limits may
be selected. They may not be added for a total
exposure of 12 hours.)

OR
• For fish that have been previously frozen:

The fish are not exposed to ambient
temperatures above 40˚F (4.4˚C) for more than
12 hours, cumulatively, if any portion of that
time is at temperatures above 70˚F (21˚C);

OR
• The fish are not exposed to ambient

temperatures above 40˚F (4.4˚C) for more than
24 hours, cumulatively, as long as no portion
of that time is at temperatures above 70˚F
(21˚C).

(Note: Only one of the above two limits may
be selected. They may not be added for a total
exposure of 12 hours.)

Enter the critical limit(s) in Column 3 of the HACCP
Plan Form.

STEP #15: ESTABLISH MONITORING
PROCEDURES.

For each processing step where “scombrotoxin forma-
tion” is identified as a significant hazard on the HACCP
Plan Form, describe monitoring procedures that will
ensure that the critical limits are consistently met.

To fully describe your monitoring program you
should answer four questions: 1) What will be
monitored? 2) How will it be monitored? 3) How
often will it be monitored (frequency)? 4) Who will
perform the monitoring?

It is important for you to keep in mind that the
feature of the process that you monitor and the
method of monitoring should enable you to deter-
mine whether the CL is being met. That is, the
monitoring process should directly measure the
feature for which you have established a CL.

You should monitor often enough so that the normal
variability in the values you are measuring will be
detected. This is especially true if these values are
typically close to the CL. Additionally, the greater
the time span between measurements the more
product you are putting at risk should a measurement
show that a CL has been violated.

Following is guidance on establishing monitoring
procedures for the control strategy examples dis-
cussed in Step #12. Note that the monitoring fre-
quencies that are provided are intended to be consid-
ered as minimum recommendations, and may not be
adequate in all cases.

Chapter 7: Histamine
90