Fume cupboards - WALDNER Laboreinrichtungen GmbH & Co. KG

Fume cupboards
for high heat and acidic load
With the title DIN EN 14175-7:2012 – Fume cupboards: Fume cupboards for high
heat and acidic load (special application fume cupboards), the seventh part of
the European series of EN 14175 standards will be issued in June 2012. The new
standard is dealing with fume cupboards for special applications, including a high
heat and/or acidic load. These special applications require additional design, safety,
operation and maintenance properties apart from those already stipulated in
the DIN EN 14175-1 to DIN EN 14175-6 standards. Utilization of these special application
fume cupboards instead of general purpose fume cupboards usually is the
result of a risk assessment. In the following an overview of the standard’s composition
in structure and content and the requirements resulting from the high heat
loads and acidic works to such special application fume cupboards will be given.
Excerpt from the foreword of DIN
EN 14175-7
The European standard EN 14175-7 has
been prepared by the technical committee
WG 4 “Fume cupboards“ within CEN/TC
332 „Laboratory equipment“. The German
mirror committee in charge is the technical
committee “Laboratory fume cupboard“
which is part of the standardization committee
“Laboratory appliances and laboratory
furniture”. It was the leading body
for the preparation of this European standard,
for which the predecessor standard
DIN 12924-2 was used as a template. This
European standard shall obtain the status
of a national standard, either by publishing
an identical text or by acknowledgement
until November 2012. Possibly conflicting
national standards shall be withdrawn until
November 2012. According to the internal
CEN/CENELEC regulations the national
standardization organizations of the following
countries are bound to implement
this European standard: Austria, Belgium,
Bulgaria, Croatia, Cyprus, Czech Republic,
Denmark, Germany, Estonia, Finland,
France, Greece, Hungary, Iceland, Ireland,
Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania,
Slovakia, Slovenia, Spain, Sweden,
Switzerland, Turkey, and United Kingdom.
Scope of DIN EN 14175-7 and alterations
in comparison with the previous
DIN 12924-2
The DIN EN 14175-7 applies for the following
special application fume cupboards:
n Fume hoods for high heat loads
n Fume hoods for high heat loads in
combination with acidic digestions
n Fume hoods for handling of perchloric
acid
n Fume hoods for handling of hydrofluoric
acid

It specifies supplementary specifications
and tests for these special application fume
cupboards that are relevant to terms, safety
and performance requirements, type test
and onsite test methods as well as their
marking.
In comparison with the predecessor standard
DIN 12924-2 the following essential
alterations have been made:
n Requirements and tests for the four special
application fume cupboard types are
separately structured and formulated
throughout
n Dimensional requirements have been deleted
from the standard
n Admissible materials for the sash have
been limited
n Marking for the purpose of conformity
will be changed with the standard
n Basic requirements for the supplier’s declaration
of conformity have been specified
Basic safety and performance
targets
For all four fume cupboard types dealt
with in the standard the following basic
safety and performance targets apply in
accordance with EN 14175-2 with supplements
such as e.g.:
Fume cupboards for high heat load and
acidic digestions
n shall guarantee the safety and performance
targets during works with high
heat loads in the fume cupboard interior
n shall prevent hazardous concentrations
and precipitations of acids and caustic
solutions that are released in the interior
and shall withstand the increased requirements
during the planned time of
utilization.
Fume cupboards for handling of perchloric
acid
Design and execution of the fume cupboard
shall guarantee the avoidance of hazardous
precipitations and hazardous reactions with
the materials used for the fume cupboard
construction during works with perchloric
acid in the fume cupboard interior.
Material requirements
In case of fume cupboards for high heat
loads the materials that are used, be it
glass, plastic or other materials, shall be
suitable with regard to their chemical resistance
and heat load capacity for the respective
working temperatures. For works with
heat load or acidic digestions the materials
shall be suitable with regard to the chemical
resistance against acids and acid vapors
and with regard to heat deformation for
the respective working temperatures. Acid
vapors occurring during digestions are extremely
viscid and connect to surfaces they
get in contact with. Materials shall have
even and easy to clean surfaces. If glass is
used as the material for the sash, official
bodies or clients in some European countries
require laminated safety glass as per the
definition given in the EN ISO 1253-1:2011
standard.
In case of fume cupboards for handling of
perchloric acid the materials used may not
react with perchloric acid nor may create
neither combustible nor explosive compounds.
The selection of the materials shall
be made with regard to the chemical resistance
and deformation against perchloric
acid at the planned working temperature.
In case of fume cupboards for handling
of hydrofluoric acid all parts of the fume
cupboards and of the exhaust air ducts that
are in contact with hydrofluoric vapors shall
consist of materials resistant against hydrofluoric
acid. The sash of those fume cupboards
shall be made of a suitable plastic
material.
Constructional requirements
Beyond the constructional requirements stipulated
in the EN 14175-2 standard it applies
that material for and execution of the
sash may neither interfere neither with the
operation nor with the safety at the temperatures
in the fume cupboard interior. In
case of fume cupboards for acidic digestions
the joints in the fume cupboard interior
shall be limited to the necessary and
sealings shall be durable, impermeable and
permanently elastic. For the work surface
in particular, seamless materials made of
one block should be given preference. The
fume cupboard’s construction shall provide
the required access to clean the worktop
surfaces, the sash and baffle plates as well
as the appliances to avoid, reduce or remove
vapors, in so far as these appliances
are part of the fume cupboard.
In case of fume cupboards for handling of
perchloric acid the fume cupboard interior
and the exhaust air zone shall be designed
in such a way that they can be cleaned in
all parts by either spurting out or by scouring
through installed jets. Cleaning requirements
for the part of the exhaust air duct
system that is not part of the fume cupboard
shall be considered. With regard to
the fume cupboard’s execution the collection
of sprinkling liquid from the exhaust air
duct system should be taken into account.
This requirement serves the avoidance of
hazardous precipitation and not for the
cleaning of the exhaust air. If fume cupboards
for handling of perchloric acid are
equipped with integrated acid fume scrubbers
or with integrated acid exhaust air
sprinklers the design shall allow full access
for cleaning and maintenance purposes.
Airflow and control requirements
Effects on the airflow, caused by heat load
and heating devices as well as by integrated
acid exhaust air scrubbers or integrated
acid exhaust air sprinklers, shall be taken
into account and shall also be limited.
In addition to the fume cupboard function
display with acoustic and visual alarm in accordance
with EN 14175-2 the fume cupboards
shall be equipped for high heat load
and with a temperature sensor at the fume
cupboard top, which releases an alarm as
soon as the exhaust air’s maximum temperature
defined in the user manual is exceeded.
It should be possible to redirect this
alarm.
Testing of fume cupboards with
high heat load
The type test shall be executed in accordance
with EN 14175-3 and on-site tests
shall be executed in accordance with EN
14175-4 with the following supplements: Unter der Annahm
During the tests two heating plates Unter shall Unter be der der Annahm
kW für einen Annahm Abzu
located in the fume cupboard interior. kW Containment
behavior and robustness shall be
kW für für einen einen Abzu
tested without heat load (with switchedoff
heating plates) and with a heat load of
4 kW per meter of the fume cupboard’s inside
width each.
Arrangement of heating plates and test gas
outlets in accordance with EN 14175-7
Nach dieser Berec
Nach Nach dieser dieser Berec
knapp 30°C anstei
knapp knapp 30°C 30°C ansteig
zug durchströmen
zug zug durchströmend
vom Material des
vom vom Material Material des
abgegeben wird. des T
abgegeben abgegeben wird. wird. T
dem, dass sich, auf
dem, dem, dass dass sich, sich, auf
innenraums im Str au
innenraums innenraums im im Stra
Innenseite des Fron
Innenseite Innenseite des des Fron
Die Hersteller von
Die Die Hersteller Hersteller von
Auswahl der verw
Auswahl Auswahl der der verw
anderen auch weit verw
anderen anderen auch auch weit
len, Rechnung trag wei
len, len, Rechnung Rechnung trag
Die Einflüsse hohe
Die Die Einflüsse Einflüsse hohe
z. B. mit den Mitte
z. z. B. B. mit mit den den Mittel Mitte

Declaration of conformity
A declaration of conformity shall clearly
state the special field of application of the
respective special application fume cupboard,
together with the planned temperature
range, and shall also confirm that the
materials and the execution of the fume
cupboard are suitable for the special application.
Implementation of the standard’s
requirements into practical work
To implement the requirements of the DIN
EN 14175-7 standard into practical work,
particularly with regard to the effects of the
high heat load, theoretical preliminary considerations
and experimental examinations
are very useful.
The heat flow supplied through the heat
capacity leads to an increase of temperature
∆ T in the fume cupboard interior that
can be calculated as per the following:
· ·
· · ·
·
·· ·
Q= m∙QQ ∙ ∆T
·· ·· ·
·
Q= V∙ρ∙QQ ∙ ∆T
∆T= QV∙ρ∙QQ
··
·· ··
According to this calculation the temperature
of the air intake in the fume cupboard
would increase for almost 30° C. Measurements
during the experiment show that the
heating of the air that is flowing through
the fume cupboard is slightly lower in reality,
because part of the heat energy is absorbed
by the fume cupboard casing’s material
and released to the outside through
its surface. Temperature measurement at
different locations in the fume cupboard
furthermore show that due to the heat radiation
of the heating plates the surfaces
of the fume cupboard interior in the radiation
area, e.g. on the fume cupboard rear
wall, will be heated up to a temperature of
95° C, or on the inside of the sash up to a
temperature of 65° C.
Therefore the manufacturers of fume cupboards
for high heat loads shall take care
of a sufficient temperature resistance when
selecting the materials to be used. Furthermore
they also have to take into account
more extensive effects such as e.g. a strong
heating of control units.
The influences of high heat loads to the
flow mechanics of the fume cupboard can
be clearly illustrated by means of e.g. a numerical
flow simulation (CFD).
On the assumption of an exhaust airflow of
By directly comparing “cold“ and “hot“ the
e eines Abluftvolumenstroms 600 m³/h and a heat capacity von 600 of m³/h 6 kW und for einer a Heizleistung von 6
computer simulation shows that the flow
me e eines eines Abluftvolumenstroms fume Abluftvolumenstroms cupboard with a von von width 600 600 of m³/h m³/h 1500 und und mm einer einer Heizleistung Heizleistung von von 6
ug mit einer Breite von 1500mm ergibt sich:
6
velocities in the fume cupboard are heavily
influenced by the heat energy released
ug g mit mit einer einer the Breite following Breite von von 1500mm result 1500mm is obtained: ergibt ergibt sich: sich:
from the heating plates. The changes of the
∆T= 6000 QQ600 Q³h∙1,2
6000
6000 QQQ3∙1005 QQQ ∙K
6000
flow velocities are inevitably accompanied
600
by a clear change of the complete flow
∆T= 29,85600 600 Q
· 1,2
·
· 1,2 1,2 · · · 1005
1005
1005
·
pattern in the fume cupboard. Thereof the
·
·
obvious assumption can be deduced that
2,5
the containment of a fume cupboard in
2,5 2,5
chnung würde die Temperatur der einströmenden Luft im Abzug um
echnung würde würde die die Temperatur Temperatur der der einströmenden einströmenden Luft Luft im im Abzug Abzug um
igen. Messungen im Experiment zeigen, dass die Erwärmung der den Abden
Luft in der Realität etwas geringer ist, da ein Teil der Wärmeenergie Ab‐
um
igen. igen. Messungen Messungen im im Experiment Experiment zeigen, zeigen, dass dass die die Erwärmung Erwärmung der der den den Abnden
Luft Luft in in der der Realität Realität etwas etwas geringer geringer ist, ist, da da ein ein Teil Teil der der Wärmeenergie
Abzugsgehäuses aufgenommen und über seine Oberfläche Wärmeenergie
nach außen
s Abzugsgehäuses Abzugsgehäuses aufgenommen aufgenommen und und über über seine seine Oberfläche Oberfläche nach nach außen
Temperaturmessungen an verschiedenen Stellen im Abzug zeigen außerfgrund
der Wärmestrahlung der Heizplatten, die Oberflächen des Abzugs‐
außer‐
außen
Temperaturmessungen an an verschiedenen verschiedenen Stellen Stellen im im Abzug Abzug zeigen zeigen außerufgrund
der der Wärmestrahlung Wärmestrahlung der der Heizplatten, Heizplatten, die die Oberflächen Oberflächen des des Abzugsrahlungsbereich,
z. B. an der Abzugsrückwand auf bis zu 95° C oder Abzugstrahlungsbereich,
z. z. B. B. an an der der Abzugsrückwand Abzugsrückwand auf auf bis bis zu zu 95° 95° C oder oder an an der
an der
ntschiebers auf bis zu 65° C erwärmen.
der
ontschiebers auf auf bis bis zu zu 65° 65° C erwärmen.
n Abzügen für hohe thermische erwärmen. Lasten müssen also zum einen bei der
n n Abzügen Abzügen für für hohe hohe thermische thermische Lasten Lasten müssen müssen also also zum zum einen einen bei bei der
endeten Werkstoffe auf genügend Temperaturfestigkeit achten und zum der
wendeten Werkstoffe Werkstoffe auf auf genügend genügend Temperaturfestigkeit Temperaturfestigkeit achten achten und und zum
terreichenden Effekten, wie z. B. einer starken Erwärmung von Bedienteigen.
Bedientei‐
zum
terreichenden iterreichenden Effekten, Effekten, wie wie z. z. B. B. einer einer starken starken Erwärmung Erwärmung von von Bedienteigen.
er thermischer Lasten auf die Strömungsmechanik des Abzugs lassen sich
er er thermischer thermischer Lasten Lasten auf auf die die Strömungsmechanik Strömungsmechanik des des Abzugs Abzugs lassen lassen sich
ln der numerischen Strömungssimulation (CFD) anschaulich darstellen. sich
eln der der numerischen numerischen Strömungssimulation Strömungssimulation (CFD) (CFD) anschaulich anschaulich darstellen. darstellen.
accordance with EN 14175-2 which considerably
depends on the routing of the
flow and the distribution of the extraction
in the fume cupboard interior, and which
had been aerodynamically optimized under
isothermal conditions, is influenced by
the source of heat. Containment measurements
with switched-on heating plates
are confirming this thesis. They show that
no satisfying containment can be achieved
with the common exhaust air flows of a
general purpose fume cupboard in accordance
with EN 14175-2.
Continuing measurements reveal that solely
by increasing the exhaust air flow to
about twice the normal values – which
also corresponds to a duplication of the
fume cupboard’s energy demand – does
not represent a sufficient measure to safely
operate the fume cupboard with high heat
load by meeting all operating conditions
stipulated in the standard.
During experimental examinations it can
be shown in a first step by means of e.g.
a flow visualization with smoke, that by assimilating
the interior room geometry and
the distribution of the extraction, the fume
cupboard’s exhaust air flow required for a
safe operation under high heat load does
not have to be duplicated in comparison
with a general purpose fume cupboard.
However, it will quickly become clear that
an optimization of the flow routing “hot“
the fume cupboard containment “cold“
will be disturbed and vice versa. To solve
such target conflicts and to find the utmost
balance between energy demand and safety
further aerodynamic examinations and
the respective development works are required.
Velocity vectors in the fume hood interior, with and without source of heat

heating plates on
heating plates off
Testing device for the robustness test
Robustness of containment, with and without heating plates
Summary
While the previous series of EN 14175 standards
exclusively described isothermal conditions
in the fume cupboard, the newly
issued part 7 offers the option to assess the
safety of fume cupboards at high heat load.
This closes an essential gap, as works with
sources of heat in a fume cupboard are part
of the daily routine in many laboratories.
Now it is not least up to the manufacturers
to translate the non-trivial requirements of
the standard into innovative solutions and
to also contribute to the safety and power
efficiency for the operation of special application
fume cupboards in laboratories.
Visualization of flow, left: heating plates switched off, right: heating plates switched on
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