Fume cupboards - WALDNER · Summary While the previous series of EN 14175 stan - dards exclusively described isothermal con-ditions in the fume cupboard, the newly issued part 7 offers

Summary

While the previous series of EN 14175 stan-dards exclusively described isothermal con-ditions 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 appli-cation fume cupboards in laboratories.

Testing device for the robustness test Robustness of containment, with and without heating plates

Visualization of flow, left: heating plates switched off, right: heating plates switched on

WALDNER Laboreinrichtungen GmbH & Co. KG I Haidösch 1 I D-88239 Wangen im AllgäuPhone +49 7522/986-0 I Fax +49 7522/986-280 I www.waldner-lab.com

heating plates on heating plates off

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 com-mittee “Laboratory appliances and labo-ratory furniture”. It was the leading body for the preparation of this European stan-dard, 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 Possibly conflicting national standards shall be withdrawn until November 2012.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 inter-nal CEN/CENELEC regulations the national standardization organizations of the fol-lowing countries are bound to implement

this European standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Repub-lic, Denmark, Germany, Estonia, Finland, France, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Ro-mania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey, and United Kingdom.

Scope of DIN EN 14175-7 and alte-rations in comparison with the pre-vious DIN 12924-2

The DIN EN 14175-7 applies for the fol-lowing 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 per- chloric acid

n Fume hoods for handling of hydro- fluoric acid

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, safe-ty, 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 appli-cation 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 compo-sition 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.

Fume cupboards for high heat and acidic load

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 stan-dard DIN 12924-2 the following essential alterations have been made:

n Requirements and tests for the four spe-cial application fume cupboard types are separately structured and formulated throughout

n Dimensional requirements have been de-leted 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 de-claration of conformity have been speci-fied

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 supple-ments such as e.g.:

Fume cupboards for high heat load and acidic digestions

n shall guarantee the safety and perfor-mance 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 interi-or and shall withstand the increased re-quirements during the planned time of utilization.

Fume cupboards for handling of per-chloric 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 resis-tance and heat load capacity for the respec-tive working temperatures. For works with heat load or acidic digestions the materials shall be suitable with regard to the chemi-cal resistance against acids and acid vapors

and with regard to heat deformation for the respective working temperatures. Acid vapors occurring during digestions are ext-remely 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 com-pounds. The selection of the materials shall be made with regard to the chemical resis-tance 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 hydro-fluoric acid. The sash of those fume cup-boards shall be made of a suitable plastic material.

Constructional requirements Beyond the constructional requirements sti-pulated in the EN 14175-2 standard it ap-plies that material for and execution of the sash may neither interfere neither with the operation nor with the safety at the tem-peratures in the fume cupboard interior. In case of fume cupboards for acidic digesti-ons the joints in the fume cupboard inte-rior 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 re-move 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 scou-ring through installed jets. Cleaning requi-rements for the part of the exhaust air duct system that is not part of the fume cup-board shall be considered. With regard to the fume cupboard’s execution the collec-tion 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 cup-boards for handling of perchloric acid are

equipped with integrated acid fume scrub-bers 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 integra-ted 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 ac-cordance with EN 14175-2 the fume cup-boards 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 tempe-rature defined in the user manual is excee-ded. It should be possible to redirect this alarm.

Testing of fume cupboards with high heat load

The type test shall be executed in ac-cordance with EN 14175-3 and on-site tests shall be executed in accordance with EN 14175-4 with the following supplements: During the tests two heating plates shall be located in the fume cupboard interior. Con-tainment behavior and robustness shall be tested without heat load (with switched-off heating plates) and with a heat load of 4 kW per meter of the fume cupboard’s in-side width each.

Arrangement of heating plates and test gas outlets in accordance with EN 14175-7

Declaration of conformity

A declaration of conformity shall clearly state the special field of application of the respective special application fume cup-board, together with the planned tempera-ture range, and shall also confirm that the materials and the execution of the fume cupboard are suitable for the special appli-cation.

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 con-siderations and experimental examinations are very useful.

The heat flow supplied through the heat capacity leads to an increase of tempera-ture ∆ T in the fume cupboard interior that can be calculated as per the following:

𝑄= 𝑄∙𝑄𝑄 ∙ ∆𝑄𝑄= 𝑄∙𝑄∙𝑄𝑄 ∙ ∆𝑄∆𝑄= 𝑄𝑄∙𝑄∙𝑄𝑄

On the assumption of an exhaust airflow of 600 m³/h and a heat capacity of 6 kW for a fume cupboard with a width of 1500 mm the following result is obtained:

∆𝑄= 6000 𝑄𝑄600 𝑄³h∙1,2 𝑄𝑄𝑄3∙1005 𝑄𝑄𝑄 ∙𝑄

∆𝑄= 29,85 𝑄

According to this calculation the tempera-ture of the air intake in the fume cupboard would increase for almost 30° C. Measure-ments during the experiment show that the heating of the air that is flowing through the fume cupboard is slightly lower in rea-lity, because part of the heat energy is ab-sorbed by the fume cupboard casing’s ma-terial and released to the outside through its surface. Temperature measurement at different locations in the fume cupboard furthermore show that due to the heat ra-diation of the heating plates the surfaces of the fume cupboard interior in the radia-tion 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 cup-boards for high heat loads shall take care of a sufficient temperature resistance when selecting the materials to be used. Further-more 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 nu-merical flow simulation (CFD).

By directly comparing “cold“ and “hot“ the computer simulation shows that the flow velocities in the fume cupboard are heavi-ly influenced by the heat energy released from the heating plates. The changes of the flow velocities are inevitably accompanied by a clear change of the complete flow pattern in the fume cupboard. Thereof the obvious assumption can be deduced that the containment of a fume cupboard in

accordance with EN 14175-2 which con-siderably depends on the routing of the flow and the distribution of the extraction in the fume cupboard interior, and which had been aerodynamically optimized un-der isothermal conditions, is influenced by the source of heat. Containment measu-rements 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 accor-dance with EN 14175-2.

Continuing measurements reveal that so-lely 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 as-similating 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 sa-fety further aerodynamic examinations and the respective development works are re-quired.

Velocity vectors in the fume hood interior, with and without source of heat

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   Unter der Annahme eines Abluftvolumenstroms von 600 m³/h und einer Heizleistung von 6 kW für einen Abzug mit einer Breite von 1500mm ergibt sich:  

�� � 6000 ��

600 ��� · 1,2 ��

�� · 1005 ��� ·�

 �� � 2�,�5 � 

 Nach  dieser  Berechnung  würde  die  Temperatur  der  einströmenden  Luft  im  Abzug  um knapp 30°C ansteigen. Messungen im Experiment zeigen, dass die Erwärmung der den Ab‐zug durchströmenden Luft in der Realität etwas geringer ist, da ein Teil der Wärmeenergie vom Material  des Abzugsgehäuses  aufgenommen  und  über  seine Oberfläche  nach  außen abgegeben wird. Temperaturmessungen an verschiedenen Stellen  im Abzug zeigen außer‐dem, dass sich, aufgrund der Wärmestrahlung der Heizplatten, die Oberflächen des Abzugs‐innenraums im Strahlungsbereich, z. B. an der Abzugsrückwand auf bis zu 95° C oder an der Innenseite des Frontschiebers auf bis zu 65° C erwärmen.  Die Hersteller  von Abzügen  für  hohe  thermische  Lasten müssen  also  zum  einen  bei  der Auswahl der verwendeten Werkstoffe auf genügend Temperaturfestigkeit achten und zum anderen auch weiterreichenden Effekten, wie z. B. einer starken Erwärmung von Bedientei‐len, Rechnung tragen.  Die Einflüsse hoher thermischer Lasten auf die Strömungsmechanik des Abzugs lassen sich z. B. mit den Mitteln der numerischen Strömungssimulation (CFD) anschaulich darstellen.  

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�� � ���� · � · ��

   Unter der Annahme eines Abluftvolumenstroms von 600 m³/h und einer Heizleistung von 6 kW für einen Abzug mit einer Breite von 1500mm ergibt sich:  

�� � 6000 ��

600 ��� · 1,2 ��

�� · 1005 ��� ·�

 �� � 2�,�5 � 

 Nach  dieser  Berechnung  würde  die  Temperatur  der  einströmenden  Luft  im  Abzug  um knapp 30°C ansteigen. Messungen im Experiment zeigen, dass die Erwärmung der den Ab‐zug durchströmenden Luft in der Realität etwas geringer ist, da ein Teil der Wärmeenergie vom Material  des Abzugsgehäuses  aufgenommen  und  über  seine Oberfläche  nach  außen abgegeben wird. Temperaturmessungen an verschiedenen Stellen  im Abzug zeigen außer‐dem, dass sich, aufgrund der Wärmestrahlung der Heizplatten, die Oberflächen des Abzugs‐innenraums im Strahlungsbereich, z. B. an der Abzugsrückwand auf bis zu 95° C oder an der Innenseite des Frontschiebers auf bis zu 65° C erwärmen.  Die Hersteller  von Abzügen  für  hohe  thermische  Lasten müssen  also  zum  einen  bei  der Auswahl der verwendeten Werkstoffe auf genügend Temperaturfestigkeit achten und zum anderen auch weiterreichenden Effekten, wie z. B. einer starken Erwärmung von Bedientei‐len, Rechnung tragen.  Die Einflüsse hoher thermischer Lasten auf die Strömungsmechanik des Abzugs lassen sich z. B. mit den Mitteln der numerischen Strömungssimulation (CFD) anschaulich darstellen.  

�� � �� · �� · �� �� � �� · � · �� · �� 

�� � ���� · � · ��

   Unter der Annahme eines Abluftvolumenstroms von 600 m³/h und einer Heizleistung von 6 kW für einen Abzug mit einer Breite von 1500mm ergibt sich:  

�� � 6000 ��

600 ��� · 1,2 ��

�� · 1005 ��� ·�

 �� � 2�,�5 � 

 Nach  dieser  Berechnung  würde  die  Temperatur  der  einströmenden  Luft  im  Abzug  um knapp 30°C ansteigen. Messungen im Experiment zeigen, dass die Erwärmung der den Ab‐zug durchströmenden Luft in der Realität etwas geringer ist, da ein Teil der Wärmeenergie vom Material  des Abzugsgehäuses  aufgenommen  und  über  seine Oberfläche  nach  außen abgegeben wird. Temperaturmessungen an verschiedenen Stellen  im Abzug zeigen außer‐dem, dass sich, aufgrund der Wärmestrahlung der Heizplatten, die Oberflächen des Abzugs‐innenraums im Strahlungsbereich, z. B. an der Abzugsrückwand auf bis zu 95° C oder an der Innenseite des Frontschiebers auf bis zu 65° C erwärmen.  Die Hersteller  von Abzügen  für  hohe  thermische  Lasten müssen  also  zum  einen  bei  der Auswahl der verwendeten Werkstoffe auf genügend Temperaturfestigkeit achten und zum anderen auch weiterreichenden Effekten, wie z. B. einer starken Erwärmung von Bedientei‐len, Rechnung tragen.  Die Einflüsse hoher thermischer Lasten auf die Strömungsmechanik des Abzugs lassen sich z. B. mit den Mitteln der numerischen Strömungssimulation (CFD) anschaulich darstellen.  

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 stan-dard DIN 12924-2 the following essential alterations have been made:

n Requirements and tests for the four spe-cial application fume cupboard types are separately structured and formulated throughout

n Dimensional requirements have been de-leted 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 de-claration of conformity have been speci-fied

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 supple-ments such as e.g.:

Fume cupboards for high heat load and acidic digestions

n shall guarantee the safety and perfor-mance 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 interi-or and shall withstand the increased re-quirements during the planned time of utilization.

Fume cupboards for handling of per-chloric 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 resis-tance and heat load capacity for the respec-tive working temperatures. For works with heat load or acidic digestions the materials shall be suitable with regard to the chemi-cal resistance against acids and acid vapors

and with regard to heat deformation for the respective working temperatures. Acid vapors occurring during digestions are ext-remely 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 com-pounds. The selection of the materials shall be made with regard to the chemical resis-tance 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 hydro-fluoric acid. The sash of those fume cup-boards shall be made of a suitable plastic material.

Constructional requirements Beyond the constructional requirements sti-pulated in the EN 14175-2 standard it ap-plies that material for and execution of the sash may neither interfere neither with the operation nor with the safety at the tem-peratures in the fume cupboard interior. In case of fume cupboards for acidic digesti-ons the joints in the fume cupboard inte-rior 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 re-move 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 scou-ring through installed jets. Cleaning requi-rements for the part of the exhaust air duct system that is not part of the fume cup-board shall be considered. With regard to the fume cupboard’s execution the collec-tion 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 cup-boards for handling of perchloric acid are

equipped with integrated acid fume scrub-bers 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 integra-ted 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 ac-cordance with EN 14175-2 the fume cup-boards 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 tempe-rature defined in the user manual is excee-ded. It should be possible to redirect this alarm.

Testing of fume cupboards with high heat load

The type test shall be executed in ac-cordance with EN 14175-3 and on-site tests shall be executed in accordance with EN 14175-4 with the following supplements: During the tests two heating plates shall be located in the fume cupboard interior. Con-tainment behavior and robustness shall be tested without heat load (with switched-off heating plates) and with a heat load of 4 kW per meter of the fume cupboard’s in-side width each.

Arrangement of heating plates and test gas outlets in accordance with EN 14175-7

Declaration of conformity

A declaration of conformity shall clearly state the special field of application of the respective special application fume cup-board, together with the planned tempera-ture range, and shall also confirm that the materials and the execution of the fume cupboard are suitable for the special appli-cation.

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 con-siderations and experimental examinations are very useful.

The heat flow supplied through the heat capacity leads to an increase of tempera-ture ∆ T in the fume cupboard interior that can be calculated as per the following:

𝑄= 𝑄∙𝑄𝑄 ∙ ∆𝑄𝑄= 𝑄∙𝑄∙𝑄𝑄 ∙ ∆𝑄∆𝑄= 𝑄𝑄∙𝑄∙𝑄𝑄

On the assumption of an exhaust airflow of 600 m³/h and a heat capacity of 6 kW for a fume cupboard with a width of 1500 mm the following result is obtained:

∆𝑄= 6000 𝑄𝑄600 𝑄³h∙1,2 𝑄𝑄𝑄3∙1005 𝑄𝑄𝑄 ∙𝑄

∆𝑄= 29,85 𝑄

According to this calculation the tempera-ture of the air intake in the fume cupboard would increase for almost 30° C. Measure-ments during the experiment show that the heating of the air that is flowing through the fume cupboard is slightly lower in rea-lity, because part of the heat energy is ab-sorbed by the fume cupboard casing’s ma-terial and released to the outside through its surface. Temperature measurement at different locations in the fume cupboard furthermore show that due to the heat ra-diation of the heating plates the surfaces of the fume cupboard interior in the radia-tion 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 cup-boards for high heat loads shall take care of a sufficient temperature resistance when selecting the materials to be used. Further-more 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 nu-merical flow simulation (CFD).

By directly comparing “cold“ and “hot“ the computer simulation shows that the flow velocities in the fume cupboard are heavi-ly influenced by the heat energy released from the heating plates. The changes of the flow velocities are inevitably accompanied by a clear change of the complete flow pattern in the fume cupboard. Thereof the obvious assumption can be deduced that the containment of a fume cupboard in

accordance with EN 14175-2 which con-siderably depends on the routing of the flow and the distribution of the extraction in the fume cupboard interior, and which had been aerodynamically optimized un-der isothermal conditions, is influenced by the source of heat. Containment measu-rements 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 accor-dance with EN 14175-2.

Continuing measurements reveal that so-lely 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 as-similating 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 sa-fety further aerodynamic examinations and the respective development works are re-quired.

Velocity vectors in the fume hood interior, with and without source of heat

�� � �� · �� · �� �� � �� · � · �� · �� 

�� � ���� · � · ��

   Unter der Annahme eines Abluftvolumenstroms von 600 m³/h und einer Heizleistung von 6 kW für einen Abzug mit einer Breite von 1500mm ergibt sich:  

�� � 6000 ��

600 ��� · 1,2 ��

�� · 1005 ��� ·�

 �� � 2�,�5 � 

 Nach  dieser  Berechnung  würde  die  Temperatur  der  einströmenden  Luft  im  Abzug  um knapp 30°C ansteigen. Messungen im Experiment zeigen, dass die Erwärmung der den Ab‐zug durchströmenden Luft in der Realität etwas geringer ist, da ein Teil der Wärmeenergie vom Material  des Abzugsgehäuses  aufgenommen  und  über  seine Oberfläche  nach  außen abgegeben wird. Temperaturmessungen an verschiedenen Stellen  im Abzug zeigen außer‐dem, dass sich, aufgrund der Wärmestrahlung der Heizplatten, die Oberflächen des Abzugs‐innenraums im Strahlungsbereich, z. B. an der Abzugsrückwand auf bis zu 95° C oder an der Innenseite des Frontschiebers auf bis zu 65° C erwärmen.  Die Hersteller  von Abzügen  für  hohe  thermische  Lasten müssen  also  zum  einen  bei  der Auswahl der verwendeten Werkstoffe auf genügend Temperaturfestigkeit achten und zum anderen auch weiterreichenden Effekten, wie z. B. einer starken Erwärmung von Bedientei‐len, Rechnung tragen.  Die Einflüsse hoher thermischer Lasten auf die Strömungsmechanik des Abzugs lassen sich z. B. mit den Mitteln der numerischen Strömungssimulation (CFD) anschaulich darstellen.  

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   Unter der Annahme eines Abluftvolumenstroms von 600 m³/h und einer Heizleistung von 6 kW für einen Abzug mit einer Breite von 1500mm ergibt sich:  

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600 ��� · 1,2 ��

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 �� � 2�,�5 � 

 Nach  dieser  Berechnung  würde  die  Temperatur  der  einströmenden  Luft  im  Abzug  um knapp 30°C ansteigen. Messungen im Experiment zeigen, dass die Erwärmung der den Ab‐zug durchströmenden Luft in der Realität etwas geringer ist, da ein Teil der Wärmeenergie vom Material  des Abzugsgehäuses  aufgenommen  und  über  seine Oberfläche  nach  außen abgegeben wird. Temperaturmessungen an verschiedenen Stellen  im Abzug zeigen außer‐dem, dass sich, aufgrund der Wärmestrahlung der Heizplatten, die Oberflächen des Abzugs‐innenraums im Strahlungsbereich, z. B. an der Abzugsrückwand auf bis zu 95° C oder an der Innenseite des Frontschiebers auf bis zu 65° C erwärmen.  Die Hersteller  von Abzügen  für  hohe  thermische  Lasten müssen  also  zum  einen  bei  der Auswahl der verwendeten Werkstoffe auf genügend Temperaturfestigkeit achten und zum anderen auch weiterreichenden Effekten, wie z. B. einer starken Erwärmung von Bedientei‐len, Rechnung tragen.  Die Einflüsse hoher thermischer Lasten auf die Strömungsmechanik des Abzugs lassen sich z. B. mit den Mitteln der numerischen Strömungssimulation (CFD) anschaulich darstellen.  

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   Unter der Annahme eines Abluftvolumenstroms von 600 m³/h und einer Heizleistung von 6 kW für einen Abzug mit einer Breite von 1500mm ergibt sich:  

�� � 6000 ��

600 ��� · 1,2 ��

�� · 1005 ��� ·�

 �� � 2�,�5 � 

 Nach  dieser  Berechnung  würde  die  Temperatur  der  einströmenden  Luft  im  Abzug  um knapp 30°C ansteigen. Messungen im Experiment zeigen, dass die Erwärmung der den Ab‐zug durchströmenden Luft in der Realität etwas geringer ist, da ein Teil der Wärmeenergie vom Material  des Abzugsgehäuses  aufgenommen  und  über  seine Oberfläche  nach  außen abgegeben wird. Temperaturmessungen an verschiedenen Stellen  im Abzug zeigen außer‐dem, dass sich, aufgrund der Wärmestrahlung der Heizplatten, die Oberflächen des Abzugs‐innenraums im Strahlungsbereich, z. B. an der Abzugsrückwand auf bis zu 95° C oder an der Innenseite des Frontschiebers auf bis zu 65° C erwärmen.  Die Hersteller  von Abzügen  für  hohe  thermische  Lasten müssen  also  zum  einen  bei  der Auswahl der verwendeten Werkstoffe auf genügend Temperaturfestigkeit achten und zum anderen auch weiterreichenden Effekten, wie z. B. einer starken Erwärmung von Bedientei‐len, Rechnung tragen.  Die Einflüsse hoher thermischer Lasten auf die Strömungsmechanik des Abzugs lassen sich z. B. mit den Mitteln der numerischen Strömungssimulation (CFD) anschaulich darstellen.  

Summary

While the previous series of EN 14175 stan-dards exclusively described isothermal con-ditions 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 appli-cation fume cupboards in laboratories.

Testing device for the robustness test Robustness of containment, with and without heating plates

Visualization of flow, left: heating plates switched off, right: heating plates switched on

WALDNER Laboreinrichtungen GmbH & Co. KG I Haidösch 1 I D-88239 Wangen im AllgäuPhone +49 7522/986-0 I Fax +49 7522/986-280 I www.waldner-lab.com

heating plates on heating plates off

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 com-mittee “Laboratory appliances and labo-ratory furniture”. It was the leading body for the preparation of this European stan-dard, 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 inter-nal CEN/CENELEC regulations the national standardization organizations of the fol-lowing countries are bound to implement

this European standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Repub-lic, Denmark, Germany, Estonia, Finland, France, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Ro-mania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey, and United Kingdom.

Scope of DIN EN 14175-7 and alte-rations in comparison with the pre-vious DIN 12924-2

The DIN EN 14175-7 applies for the fol-lowing 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 per- chloric acid

n Fume hoods for handling of hydro- fluoric acid

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, safe-ty, 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 appli-cation 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 compo-sition 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.

Fume cupboards for high heat and acidic load