JAPAN P& I CLUBVol.41 November 2017

P&I Loss Prevention Bulletin
The Japan Ship Owners Mutual Protection & Indemnity Association Loss Prevention and Ship Inspection Department

VENTILATION

目次

INDEX
Introduction …………………………………………………………………………………………………………… 2
Box 1

The science behind ‘sweat’ ……………………………………………………………………………… 4

Box 2

Hygroscopic cargoes, the equilibrium relative humidity, and ventilation …………………………… 7

Box 3

Bagged rice cargoes; stowage and dunnaging ……………………………………………………… 9

Box 4

Example of a standard dew point table ……………………………………………………………… 13−1−

JAPAN P& I CLUBP&I Loss Prevention Bulletin

Introduction
This article explains the basics of cargo ventilation. It
focuses on the ventilation of cargo spaces on conventional
ships and does not relate to the ventilation of containers or
refrigerated compartments. For the purpose of this article,
ventilation is defined as the intentional introduction of air
from the external environment into and through a cargospace, and the exhausting of the in-hold air. Ventilation as
so defined may be required for several reasons, but thesemainly relate to either the safety of people or the appropriate care of the cargo. The latter is the main focus of thisarticle, which covers the aims of appropriate ventilation,
the cargoes most at risk of sweat damage, and thepracticalities of applying conventional cargo ventilation.

SafetyVentilation may be needed to ensure that there is a sufficient oxygen supply for safe personnel entry into the cargo space.
Similarly, ventilation may be needed to remove poisonous and flammable gases which could give rise to a dangerous
situation. These gases might be produced by the cargo itself, e.g. evolution of carbon monoxide from a heating coal cargo.
Alternatively, they may originate from another external source, e.g. phosphine gas evolution during cargo fumigation (seeJapan P&I Loss Prevention Bulletin Vol.22, March 2012, for the dangers associated with fumigant gases). Regardless,ventilation in this sense, sometimes referred to as ‘aeration’, requires the measurement of the gases present in the air until
such a time that they can be considered to have returned to normal or ‘safe’ levels. It is not primarily concerned with thecare of the cargo.

Cargo care
Apart from the above safety reasons, the main aim of ventilating cargo spaces is to minimise condensation, or so-called‘sweat’, forming inside the cargo space. This can be an important aspect of caring for a particular cargo while it is in thecustody of the master of the carrying vessel. A failure to do so may result in cargo damage and thus a cargo claim at
outturn. When deciding whether or not to ventilate a cargo compartment to eliminate/minimise sweat formation, the crew
must measure and compare the external air temperature with that of the cargo itself, or the air inside the cargo space (moreon this later in the article).

What is sweat?
In shipping, ‘sweat’ is the term used to refer to the formation of condensation in the cargo compartment. See Box 1 formore detail on the relationship between air temperature, dew point, and sweat formation. In the context of cargo damage
arising from condensation, we tend to talk about ‘cargo sweat’ and ‘ship’s sweat’. The assignation of these terms simply
reflects the visual appearance of the phenomena, but both are misnomers since neither the cargo, nor the ship, can perspirein the true meaning of the word. These are explained in more detail here.

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JAPAN P& I CLUB

Cargo sweat
When condensation forms directly on the cargo it is referred to as‘cargo sweat’ (see Photo 1). Cargo sweat is a potential problem
when relatively cool cargoes are carried through relatively warm
climates and (inappropriately) ventilated with the warmer air. When
the warm air enters the cargo space and comes into contact with thecool cargo, water vapour will condense out into liquid water onto the
exposed surfaces of the cargo, if the air is cooled to below its dew
point. In this way, it appears that the cargo is ‘sweating’.
Formation of condensation on the surface of rolled steel cargo,
known as cargo sweat. It is most commonly a problem whencool cargoes are inappropriately ventilated with warm air.

Photo 1.

Ship's sweat
When condensation forms on the steelwork in the ship’s hold it is referred to as ‘ship’s sweat’. This commonly occurs on the
coaming and underside of the hatch covers (see Photo 2) where it may then drip back down onto the cargo surface beneath,
producing a characteristic pattern of damage (see Photo 3). Ship’s sweat typically arises when a warm or self-heating cargo
is carried through cooler climates and the headspace is not sufficiently ventilated to replace the warm moist air within it withcooler external air. As this warm moist air in the headspace comes into contact with the cool steel structures of the ship (which
are cooled by the lower external air and/or sea temperatures), the air is cooled below its dew point and water vapour condenses
into liquid water. The liquid moisture often runs down and off the surfaces, giving the appearance that the ship is ‘sweating’.

Photo 2.

Photo 3.

Formation of condensation on the underside of thehatch covers, otherwise known as shipʼs sweat,
where warm moist air meets cool steel and the
moisture vapour condenses into liquid water.

Characteristic damage to a grain cargo arising fromshipʼs sweat. A distinctive linear pattern of superficial
deterioration (discolouration and mould growth) at thesurface of the stow, where liquid moisture has drippedback down onto this bulk grain cargo from the undersideof the closed hatch covers. The banding pattern mirrors
the layout of the metal structures above.

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JAPAN P& I CLUBP&I Loss Prevention Bulletin■ VENTILATIONBox 1

The science behind ‘sweat’At any given temperature, air can hold a maximum amount of moisture as water vapour. This is referred to as thesaturation moisture content. It can be measured (either the mass of moisture in the air or the pressure exerted by thatmoisture) and standard tables have been published listing the saturation moisture content at a particular temperature.
When the air is not fully saturated at any given temperature, then the actual quantity of moisture in that air is expressed as a percentage of the saturation moisture content at that temperature. This is known as the relative humidity.
When air at a given temperature and relative humidity is cooled to the temperature at which it reaches its saturation
moisture content, that lower temperature is known as the dew point. Further cooling below the dew point temperaturecauses the moisture in the air to condense out as liquid moisture, i.e. condensation or ‘sweat’ forms.

EXAMPLE:

If that air was actually found to contain
only 10g/m3 of moisture, then its relative
humidity would be 58% (10 ÷17.30 x 100)
at 20℃ .
At 11.1℃ the mass of moisture vapour insaturated air is 10.08g/m3.
On that basis, air at 20℃ and 58%
relative humidity, would have a dew pointof 11℃ .

30

25

15

10

5

Saturation moisture
content (g/m3)

30.4

23.1 17.3 12.8

9.4

6.8

3

The amount of water vapour (g/m )According to standard tables the massof moisture in saturated air at 20℃ is
17.30g/m3.

Temperature（℃）

20

50
45
Standard table
40
35
30
25

Condensation
below 11℃

20

17.3 g/m3

15

If that same air were to be cooled below
11℃ then condensation or sweat wouldform.

If that air was actuallyfound to contain only
10g/m3 of moisture,then its relative humidity
would be 58% at 20℃.

105Because of this relationship, the dew
point can also be used as a measure of
the amount of moisture in the air.

0
0

5

10
11℃

−4−

15

20

25

30

Temperature（℃）

3540JAPAN P& I CLUBWhich cargoes are most at risk?
Cargoes that are susceptible to damage caused by sweat are those that will deteriorate in some way when in contact
with water. These cargoes may be either hygroscopic or non-hygroscopic. Hygroscopic cargoes are those which havean inherent moisture content that can interact with the air (see Box 2). Non-hygroscopic cargoes are those that do nothave an inherent moisture content, or at least not one which can interact with the air.
Typically, hygroscopic cargoes arenatural products, such as grains,oilseeds, cocoa beans, timber, etc., or
products derived from them, such as
meals, seedcakes, and other animal
feeds, etc. Such cargoes requireappropriate ventilation to eliminate orat least minimise damage arising fromcontact with liquid water. It must be
remembered that their safe carriage
is dependent on the moisture content
at which they are loaded. As a result,introduction of additional moisture(condensation) may result in localised
germination of the grains themselves
or fungal spores that are always
present. Typically, the pattern of
this deterioration closely mirrors thesource of the moisture (see Photo 3).

Photo 3

Rice packaged in woven polypropylene bags behaves as a hygroscopic cargo in relation to the air in the headspace.
Cargo claims for condensation damage to bagged rice cargoes are common, especially for the trade from South-east
Asia to West Africa. In many such cases, a characteristic pattern of damage is seen whereby the bags all around the
periphery of the stow tend to be more affected than those further into the stowage. These claims often lead to allegations of inappropriate stowage, dunnaging, and/or ventilation (see Box 3).
Cargoes such as sugar and fertiliser are theoretically hygroscopic, but are not usually ventilated. This is because
the moisture content of these cargoes is so much lower than the ventilating air, such that the cargo would almost
always absorb some moisture from the air being introduced. This may lead to a change in physical condition, such as
stickiness or ‘caking’, and ultimately a claim may be lodged on outturn from the vessel. Additionally, these cargoes
are often packaged in woven polypropylene bags with a polypropylene liner. In that case they no longer behave as aconventional hygroscopic cargo with regards to the air in the cargo space and instead the cargo interacts only with the
air inside the bag. In such circumstances, ventilation would be of little or no benefit to the cargo, but could still cause
cargo sweat damage if applied inappropriately.

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JAPAN P& I CLUBP&I Loss Prevention Bulletin
Hygroscopic cargoes might be...
localised germination of the grains themselves or fungal sporeschange in physical condition, such as stickiness or ‘caking’absorbing somemoisture from air

produce poisonous or ﬂammable gases

Other hygroscopic cargoes (e.g. coal, fishmeal, coke, direct reduced iron, etc.) can react with oxygen in the air toproduce heat and sometimes poisonous or flammable gases. In such cases, guidance from an expert is often required
to advise on a gas monitoring and ventilation regime needed to minimise the risk of a dangerous or explosive situation
developing on board the ship, but at the same time minimise the risk of introducing further air (and thus oxygen) into
the cargo space that may potentially exacerbate the situation.
Several non-hygroscopic cargoes may also be at risk of sweat damage because they interact with liquid moisture. One
common example is steel products, such as coils, sheets, pipes, etc., that may react with the moisture to form rust. See
Japan P&I Loss Prevention Bulletins Vol.19 (August 2010) and Vol. 20 (April 2011) which focus entirely on the risks
associated with the carriage of steel products. In addition to the risk of cargo sweat damage, such cargoes are often
dunnaged with large amounts of hygroscopic material (e.g. timber) which may lead to the formation of ship’s sweat if
inappropriately ventilated (see the section Taking the Decision to Ventilate for more on this).

JAPAN P& I CLUB第 19 号 2010 年 8 月

Vol.19August 2010

P&I ロス・プリベンション
プ・ガイド
P&I Loss Prevention Bulletin
編集：日本船主責任相互保険組合 損害調査部／ロス・プリベンション推進部

The Japan Ship Owners Mutual Protection & Indemnity Association
Claims Department/Loss Prevention and Ship Inspection Department

INDEX

目 次
はじめに

……………………………………… P1

Introduction ………………………………… P1

鋼材の種類…………………………………… P2

Types of Steel Product …………………… P2

一般に起こりうる損害 ………………………… P5

Types of Damage which are Commonly Sustained … P5

積荷前検査と船荷証券 …………………………P13

Pre-Loading Inspections and Bills of Lading … P13

積荷と積付 ………………………………………P15

Loading and Stowage ……………………… P15

おわりに …………………………………………P20

Final Thoughts ……………………………… P20

はじめに

Introduction

毎年何万トンもの様々な形態の鋼材が世界中でMany millions of tons of steel in its various forms areshipped around the world each year. The major exportersof steel products are Japan and Northern Europe, with

輸送されています。鋼材の主要輸出国といえば日本や北欧諸国ですが、今日ではロシアやバルト諸国、そしてブラジルやインドの輸出も増加しています。一方、米国は相当量の鋼材を輸入しており、また世界中の国々の間で多くの輸出入取引が行われています。鋼材の輸送には主に撒積貨物船が使用されており、より小規模なものでは一般貨物船による輸送がありますが、稀にコンテナ輸送を主

exports increasing from Russian, Baltic States, Brazil andIndia. The USA imports a significant quantity of steel
products and there is extensive cross-trading between othernations around the world. These days much of the steel
is carried by bulk carriers, with smaller shipments being
carried by general cargo vessels and, occasionally, byvessels designed primarily for the carriage of containers.

とする船舶によっても輸送が行われています。
Some steel products are unfinished or semi-finished and

鋼材には比較的価格の安い未完成品 / 半製品と、価格の高い完成品があります。しかし価格に関わらず、全ての鋼材は湿気による発錆や接触による物理的ダメージ、またコンタミネーションによる損傷を受けやすく、船荷証券に表示されていない
損傷や欠陥が明らかとなった場合、荷受人から運送した船舶の責任を問われる可能性が高くなります。
本号および次号では鋼材輸送に関し様々な考察を行います。本号では鋼材の種類とその積付まで

are of relatively low value, whilst other products are
finished and are of relatively high value. Regardless ofvalue, all types of steel products are susceptible to damage
by rusting following wetting, by mechanical damage
following contact and by contamination. Receivers ofsteel products which display any form of damage or defectwhich is not described on the bill of lading are likely to
pursue a claim against the carrying vessel.
In this article, the first of two which deal with the carriage
of steel products, we will discuss the various types of steel−1−

In the event of sweat damage and a cargo claim, the actions of the crew with regards to cargo stowage and ventilation
may come under scrutiny. The rest of this article covers the more practical aspects of deciding when to ventilate, howthat ventilation will be applied, and the documentation of that ventilation.

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JAPAN P& I CLUB■ VENTILATIONBox 2Hygroscopic cargoes,the equilibrium relative humidity,
and ventilation

The temperature and moisture content of the air in an unventilated cargo space containing a hygroscopic cargo isgoverned by the characteristics of the cargo itself.
Hygroscopic cargoes loaded at a given moisture content and at a particular temperature will initially either absorb
moisture from, or give up moisture to, the air surrounding the cargo. This process continues until an equilibrium isreached whereby no further absorption or desorption occurs. The relative humidity of the air adjacent to the cargo atwhich the equilibrium is reached is referred to as the Equilibrium Relative Humidity (ERH).
The ERH at the surface of many agricultural products (e.g. grains, oilseeds, etc.) determines whether or not fungal
spores (mould) at the grain surface can germinate and grow. The majority of storage fungi associated with thesecargoes can germinate at an ERH of around 65-70% or higher. The ERH will increase at higher moistures contents
or higher temperatures. This is partly the reason why such cargoes should be protected from sources of additional
moisture and heat during carriage.
Many grain cargoes are dried prior to entering into storage (whether ashore or on board a vessel for carriage) with theintention that the ERH at the surface of the grains is sufficiently low (i.e. below 65-70%) in order to minimise the riskof spoilage during carriage. Unfortunately, in reality, many cargoes shipped around the world are not sufficiently driedand spoilage from mould growth is a common result.
That being said, even when cargoes are sufficiently dried, the moisture content of many grains and oilseeds at thetime of shipment is still substantial. Many are shipped at a moisture content in excess of 10% by weight. In such a
scenario, a cargo space containing 10,000MT of grain contains a reservoir of at least 1,000MT of moisture within thatgrain. This represents a much greater quantity of moisture than can ever be contained within the air inside the hold.
This means that if conditions are such that condensation is occurring in the headspace above a hygroscopic cargo, themoisture lost from the air as condensation will be replaced by moisture from the hygroscopic cargo reservoir.
If conditions remained the same (i.e. low external air temperatures are maintained), then a continuous process ofcondensation could be established. Under such conditions, it would be necessary to ventilate to minimise damage
arising to the cargo from that condensation (i.e. ship’s sweat).

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JAPAN P& I CLUBP&I Loss Prevention Bulletin

moisture content
low external air temperatures

10,000MT of grain

grains, oilseeds

ventilation isrequiredmoisture content inexcess of 10% by weight(at least 1,000MT of moisture)condensation

The introduction of cooler air into the headspace by ventilation would result in that air being warmed by the cargo
below, since the temperature of the cargo mass governs the air temperature in the hold. As the ventilating air was
warmed, its relative humidity would reduce and moisture would be taken up into the air (until the ERH was approached).
If conditions were such that it was appropriate to continue ventilation then that ventilating air (and the moisture it
contained) would be continuously removed from the headspace, thereby minimising the risk of sweat damage. If theconditions changed such that condensation was not occurring in the headspace (i.e. external air temperatures rose, andtherefore that of the ship’s steelwork), then ventilation would no longer be required.

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JAPAN P& I CLUB■ VENTILATION

Box 3

Bagged rice cargoes;stowage and dunnaging

Cargo claims for condensation damage to bagged rice cargoes are common and are often based on allegations of
inappropriate stowage, dunnaging, and/or ventilation.
Appropriate dunnaging can minimise the risk of cargo damage from any sweat that may form. When dunnaging
is properly constructed (using flat board timber, wooden struts and/or bamboo mats) variously on the tank top andaround the sides of the stow, it can effectively maintain an air gap of a few centimetres between the cargo and thesteel structures of the ship. This means that any sweat which may form on the steelwork at the sides and bottom of the
cargo space will not come into contact with the cargo. In such a system, sweat can run freely down the steel and drain
aftwards to the hold bilges.
In more recent times, it has become common in the bagged rice trade from South-east Asia for this traditional typeof dunnaging to be replaced by the placement of Styrofoam blocks against the hull as a means of insulation, then acovering of plastic sheeting is fitted, often topped with a layer of Kraft paper, before bags are stowed against the Kraft
paper. This is sometimes called the ‘Allied’ system, after the rice trading company that introduced it. They championed the system on the basis that it insulated the cargo from the external conditions such that sweat damage would be
eliminated. While this may be true relative to the use of no dunnaging at all, in reality this has not been the case andbagged rice cargo claims arising from sweat damage have continued (with or without the use of the Allied system).
In addition, it has also become common in this trade for trenches or ‘ventilation channels’ to be built into the stowage
as the bags are stowed in the holds. Emphasis has been placed on their importance, seemingly based on a theory thatthey can in some way facilitate better exchange of air in the cargo space. However, this is unlikely to be the case.
Bagged rice cargoes are hygroscopic and the temperature and dew point of the air in the channels will be determinedby the temperature and moisture content of the rice. Therefore, the channels themselves are of little or no benefit inpreventing sweat damage. The risk of sweat forming may be just as likely for a block stowage as when ventilation
channels are built into the stowage.
Of course, as with all cargoes, care should be taken during the loading of bagged cargoes to prevent bags being stowed
in a way which would prevent the exchange of air across all parts of the headspace. Ventilation openings into thecargo space must not be obstructed.

−9−JAPAN P& I CLUBP&I Loss Prevention Bulletin
Pause for thought
Before loading commences, the Master and Chief Officer need to give careful consideration to the stowage ofthe cargo and whether or not ventilation may need to be applied during the voyage. In some cases, charterers
may have provided clear guidelines for cargo stowage and ventilation in their voyage/carriage instructions.
These should be read carefully and any queries raised prior to the voyage. When ventilation instructions havenot been provided, a prudent Master would be expected to consult standard industry reference material (e.g.
textbooks, P&I loss prevention publications, etc.) for guidelines on stowage and whether or not the cargo mayneed to be ventilated during the voyage, in addition to using his own knowledge and experience.

Taking the decision to ventilate
In order to eliminate/minimise the formation of sweat and the associated risk of cargo damage, the fundamental
decision taken by the Master to ventilate the cargo space or not should be based on either the ‘Dew Point Rule’ or the‘Three Degree Rule’. These are defined as follows:

Dew Point Rule or Three Degree RuleThe Dew Point Rule states that a cargo hold should be ventilated when the dew point of theoutside air is lower than the dew point of the air inside the cargo space.
The Three Degree Rule states that a cargo hold should be ventilated when the dry bulb
temperature of the outside air is at least 3°C lower than the temperature of the cargo.
Both rules are a suitable means of deciding whether or not it is appropriate to ventilate. The Three Degree Ruleis based on the Dew Point Rule and was derived scientifically for use with hygroscopic cargoes (assumed to be
at 70% ERH and subject to ventilating air at 80% RH). Although by definition an ERH cannot be established for
non-hygroscopic cargoes (see Box 2), the Three Degree Rule can still be extended as a general rule of thumb for
non-hygroscopic cargoes. This is because both the Three Degree Rule and the Dew Point Rule essentially seek tominimise the risk of sweat forming in the cargo space, either on the ship’s steelwork or on the cargo, by replacing
relatively warm/moist air with relatively cool/dry external air. However, there are pros and cons for using both rules.
These are briefly outlined here.
To determine the dew point of the air, it is necessary to obtain a dry bulb and a wet bulb temperature and thencompare the values to determine the dew point from standard published tables (see Box 4). The dry bulb is a standard
thermometer, whereas the bulb of the wet bulb thermometer is surrounded by a muslin wick that is submerged inpure water. To obtain an accurate reading a sufficient flow of air needs to be achieved over the wet bulb. The drier
the air that passes over the wick, the greater the amount of moisture which will be lost from the muslin to the air, andtherefore the greater the cooling effect will be on the wet bulb. The difference or ‘depression’ of the wet bulb reading
against the dry bulb reading is used with standard tables to calculate the dew point.
One wet and dry bulb pairing is normally housed in a Stevenson screen near to the bridge and it is these which are− 10 −JAPAN P& I CLUBused to measure the conditions of the external air. The location of the Stevenson screen allows for an effective air
flow over the wet bulb and means that the external air dew point can be accurately determined. The problem often
arises when trying to accurately determine the wet bulb temperature in the cargo spaces to be ventilated.
To obtain an accurate reading a sufficient flow of air needs to be achieved over the wet bulb. This can be achievedin an enclosed space by use of a whirling hygrometer. While theoretically possible in a general cargo ship, where thecargo spaces can be accessed by the crew, these days most cargoes that require ventilation are carried in bulk carriers
where it is impractical (if not impossible or unsafe) to obtain such a measurement. Furthermore, in bulk carriers the
cargo is often loaded up into the coaming space and it is difficult, if not impossible, to get accurate readings of the air
in the headspace.
Seemingly in an attempt to combat this, it has become common practice to place portable wet and dry bulb thermometers on the end of rope inside the access manholes (see Photos 4 and 5). In cases where the cargo feeder holes in the
coamings are not obstructed and the cargo is not fully loaded up into the manhole access trunkings, then the air being
measured below the accesses will be continuous with the headspace. However, this is not always the case. Moreover,in an unventilated hold there will be little or no airflow and so the wet bulb temperature cannot be accurately
determined. On the other hand, in a hold under ventilation, in all likelihood, the wet bulb would be measuring theventilating air passing through the hold, and not the hold air.

Placing of portable wet anddry bulb thermometers in theaccess manholes has becomecommonplace on board bulk
carriers, but it is extremely difﬁcult to obtain an accurate wet
bulb reading and the air may
not necessarily be connectedto the headspace in any case.
Photo 4

Photo 5

No such difficulties are faced when using the Three Degree Rule, which only requires reliable cargo temperatures
obtained during loading and reliable external dry bulb temperatures during the voyage. However, this rule makes theassumption that the cargo temperature remains relatively constant during the voyage. This is a reasonable assumption
for many cargoes, but experience shows that this is not always the case.
In cargoes, such as seed cake or soya beans, that can sometimes be loaded in a condition that leads to self-heating
during the voyage, then basing the decision to ventilate on a loading temperature may give rise to cargo damage, sincethat loading temperature may be substantially below the actual temperature of a heating cargo during the voyage.
Even if the crew suspect the cargo temperature may have altered since loading, accessing the cargo spaces during thevoyage to take additional cargo temperatures may not be practical (e.g. risk of cargo wetting from sea spray) or safe
(e.g. cargo spaces under fumigation).
− 11 −JAPAN P& I CLUBP&I Loss Prevention Bulletin
Difficulties may arise for different reasons when a combination of cargo types is being carried in a single compartment
or in different decks on board a ‘tween decker general cargo vessel. For example, steel products and timber products,
or other hygroscopic items, together in one compartment or in different decks. In that scenario, the hygroscopic cargomust be ventilated in such a way that cargo sweat does not form on the steel cargo. The temperature of the steel cargoshould be obtained during loading, as if the Three Degree Rule is to be used, and the procedures of the Dew Point
Rule may be used during the voyage to establish the dew point temperatures and a balance must then be sought so thatsweat does not form on either the steelwork of the vessel or the steel items of cargo.
For the carriage of general cargo items or mixed cargoes there are two broad rules of thumb which can be borne inmind and used in conjunction with the Rules given above, they are:
● Cold to Hot − Ventilate Not●

Hot to Cold − Ventilate Bold

Two broad rules
Cold

to

Hot
Ventilate

Ｎｏｔ
Hot

to

Cold
Ventilate

Bold
During a voyage from a cold area to a warmer area the cargo will generally remain cold while the structures ofthe vessel will get warmer and the dew point of the outside air is likely to be above the temperature of the cargo –therefore do not ventilate. Whereas during a voyage from a warmer area to a colder area the steelwork of the vessel
will become colder while the cargo will remain warm and ship’s sweat is likely to occur, at the same time the dew
point of the outside air is likely to be below that of the air inside the hold, therefore ventilate to avoid the formation of
ship’s sweat.
These examples are simplified and in practice all appropriate measurements must be taken and ventilation/no ventilation must be carried out bearing in mind all the circumstances, day to day.

− 12 −JAPAN P& I CLUB■ VENTILATION

Box 4

Example of a standard dew
point table
Applying ventilation

How ventilation is applied to a cargo space is dependent upon the ventilation system with which the ship is equipped.
Conventional ventilation systems are normally either natural (passive) or mechanical (fan-assisted). In both cases, theobject of the ventilation system is to allow replacement of air inside the cargo spaces.
To achieve this all ventilation systems must have both inlet and outlet ventilation openings at opposite ends of the
cargo space. The ventilation openings may be at deck level (sometimes in purposely designed ‘mushrooms’), in thehatch covers (see Photo 6), or sometimes on the crane masts or associated housing. This basic layout is often true ofboth natural and mechanical systems, but in the case of the latter there is an additional fan component.

Starboard side forward andaft ventilation covers in thehatch panel in the open position for natural ventilation on
board a bulk carrier. Since
natural ventilation is limited
when the vessel is stationary,
here the hatches have been
jacked-up to facilitate a better exchange of air while thevessel is alongside the berth.
Photo 6

Obviously, the crew need to be able to open or close these openings to apply or stop ventilation when conditions
dictate. It is also important that the cargo is stowed in such a way that the openings are not obstructed inside the cargospace. This is extremely difficult to rectify after the event, reinforcing the need to give careful consideration prior toloading as to whether ventilation of the cargo will be needed during the voyage.

− 13 −JAPAN P& I CLUBP&I Loss Prevention Bulletin
Dry Buld

Depression of Wet Bulb

Dry Buldlines

In the table, lines are ruled to draw attention to the fact that above the line evaporation is going on from a water surface, while below the line it is going on from an
ice surface. Owing to this, interpolation must not be made between figures on different sides of the lines.
For dry bulb temperatures below 0 ˚C it will be noted that, when the depression of the wet bulb is zero, i.e. when the temperature of the wet bulb is equal to thatof the dry bulb, the dew-point is still below the dry bulb, and the relative humidity is less than 100 per cent. These apparent anomalies are a consequence of themethod of computing dew-points and relative humidities now adopted by the Met Office, in which the standard saturation pressure for temperature below 0 ˚C istaken as that over water, and not as that over ice.

DEWPOINT TABLE
Table (7.38.1)(For use with marine screen)− 14 −JAPAN P& I CLUB

Although mechanical ventilation fans can be engaged to achieve ventilation continuously, natural ventilation systems
are largely dependent on the external wind conditions, i.e. the relative air flow across the vessel. When conditions are
such that there is no air flow over the vessel, the use of natural ventilation openings alone may not achieve a satisfactory air exchange. Under such circumstances, and only when sea/weather conditions allow, and only when the vessel
is alongside or at a sheltered anchorage, more effective ventilation can sometimes be achieved by slightly opening
the hatch covers (see Photo 7). However, during such ventilation, care needs to be taken to prevent wetting of the
cargo from external sources of moisture, such as rain. Indeed, it may not be appropriate to do this while the vessel isunderway at sea.

Since natural ventilation
is limited when the vessel
is stationar y, here therolling hatches have been
opened a little to facilitate
a better exchange of air.
Photo 7

Recording the ventilation
Regardless of the mechanism and the ventilation rule is used, taking the decision to ventilate or not requires theregular monitoring and measurement of conditions outside and inside the cargo spaces. Ventilation should also be
applied in accordance with carriage instructions provided to the Master and the weather/sea conditions at that time.
Many cargoes that require ventilating to eliminate/minimise the risk of damage from condensation are obviously
susceptible to other sources of external moisture, e.g. rain or sea spray. Thus, the risk of exposing the cargo to these
additional moisture sources must be considered. Conversely, it is not simply sufficient for the Master to ventilate
whenever the weather is “good”. This may not achieve appropriate ventilation in accordance with one of the accepted
ventilation rules, since “good” weather could translate to warm and sunny weather, i.e. potentially risking cargo sweat.
Given the ventilation rules outlined in this article, it should be obvious that conditions may well be most appropriate
for ventilation at night (when temperatures are often lowest).
The conditions should be reviewed regularly, e.g. every 4 hours on a 24 hour basis throughout the voyage. The
readings should be taken by the crew and recorded in a ventilation log, along with the actions taken at that time (seean example ventilation log at Table 1). In the event of a cargo claim, such documents can be useful evidence of theappropriateness (or not) of the cargo care regime employed by the crew during the voyage.

− 15 −JAPAN P& I CLUBP&I Loss Prevention Bulletin
Table 1. Example Ventilation Log.
External Dry Bulb

Cargo Temperature

Temperature（℃）

at loading（℃）

0000

10

23

Yes

17/01/2016

0400

11

23

Yes

17/01/2016

0800

14

23

No

17/01/2016

1200

21

23

No

Date

Time

17/01/2016

Ventilate?

Remarks
As per Three Degree Rule,ventilate
As per Three Degree Rule,ventilate
Closed vents, raining
As per Three Degree Rule,
do not ventilate

And so on…

The limitations of ventilation
It is important to realise that even if properly followed and applied, there are still limitations to how effective cargoventilation can be. Sweat may still unavoidably form even if the cargo was appropriately ventilated. This may be aconsequence of the weather and sea conditions during the voyage and/or the cargo condition. It could also simply
be a reflection that conventional ventilation can only really minimise sweat formation in the headspace, with limited
impact elsewhere in the cargo space. For bulk cargoes, the vast majority of the cargo will be unaffected by theventilating air. Regardless, having documentary evidence that the crew gave due consideration prior to loading to thestowage and possible need for ventilation, as well as a record of the decisions and actions taken with regards to cargoventilation during the voyage, can be of great assistance in defending against claims for cargo damage due to sweat.

With collaboration from Brookes Bell

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