KANBrief 3/14

Can laboratory ventilation be both effective and energy- efficient?

One purpose of laboratory fume cupboards is to protect workers against dangerous substances at work. In certain situations however, the performance of some fume cupboards is unsatisfactory, even though they comply with the standards. Standardization must rectify this deficit. A ventilation situation typically encountered in a laboratory must not impair the safety of fume cupboards and other ventilation safety equipment. Human safety is the top priority here.

Laboratory equipment includes exhaust air equipment such as fume cupboards, safety benches, local exhaust systems, safety cabinets, and underfloor fume exhaust systems. This equipment has the function of exhausting hazardous substances. Depending upon its type and design, it may however have further safety functions. In the case of fume cupboards for example, these include providing protection against explosion by purging the interior of the cupboard, and assuring protection against splashing and flying fragments.

The essential challenge lies in controlling and routing the numerous exhaust and – where applicable – supply air flows such that adequate consideration is given to safety, the room climate (draughts, temperature, atmospheric humidity), the flexibility of the laboratory's use, and energy efficiency.

Laboratory ventilation design must also consider the increasing density of equipment at laboratory workstations, the growing number of items of electrical equipment and their increasing power consumption (thermal load), and the mixed use that is common in practice (such as more documentation workstations).

Cases are known in which in certain laboratory situations (such as glass façades, special vent outlets, very cold supply air, air obstructions), the containment capacity of fume cupboards was unsatisfactory despite the specified flow rates being observed and robustness tests being passed. The resulting call sometimes heard for all installed ventilated equipment to be tested in-situ under operating conditions or to be checked by computer-aided methods (3DCFD) is however questionable, not least owing to the impossibility of simulating all operating conditions efficiently in-situ and in a short time.

Ventilation problems and strategies for solutions

Several strategies for the prevention of ventilation problems on fume cupboards are currently followed in standardization and legislation:

1. The EN 141751 series of standards characterizes the properties of laboratory fume cupboards by type tests and in-situ test methods. For this purpose, a ventilation "robustness test" was developed: a large plate is moved along the front of the fume cupboard at a velocity of 1 m/s, deficiencies in the cupboard's containment capacity being detected by the emission of tracer gases.

(Information: EN 14175, Fume cupboards 1 Vocabulary, 2 Safety and performance requirements, 3 Type test methods, 4 On-site test methods, 5 Installation and maintenance, 6 Variable air volume fume cupboards, 7 Fume cupboards for high heat and acidic load)

2. The CEN/TC 332/WC 4 committee, Laboratory Equipment, is discussing for example how vertical disruption to the airflow inside the fume cupboard can be considered in extended robustness tests and as early as the laboratory planning phase.

3. VDI 2051, Ventilation of laboratories, is to be revised and is to supplement DIN 1946-7, Ventilation and air conditioning – Ventilation systems in laboratories. The German Social Accident Insurance Institutions also address this topic in the BGI/GUV-I 850-0 laboratory codes.

Reduction in exhaust air volume flow exacerbates the problem

Owing to the high energy losses associated with ventilation, efforts are being made to reduce laboratory exhaust volumes drastically. This can however, for example when the sash of the cupboard is closed, lead to the thermal load in the laboratory rising, particularly in the summer, to a degree that cooling is then possible only with high temperature differences (and consequently downward airflows which provoke loss of performance). The risk also arises of an explosive atmosphere being formed inside fume cupboards, for example during the handling of solvents. Substantially more radical concepts, such as recirculation of filtered air instead of exhaust, or exhaust of the air only when its contamination is measurable, can be ruled out for occupational safety and health reasons.

Tasks of standards developers and legislators

In order for laboratory ventilation to function properly, standards developers must both develop ventilation quality criteria further, and develop practical minimum requirements for the planning and execution of laboratory ventilation arrangements. This particularly applies to the objective of a low-disruption supply air flow. It is desirable for the occupational safety and health lobby to support standards developers by contributing their expertise in the area of hazardous substances and working procedures.

Dr. Albrecht K. Blob