Process ventilation

Replaced air supply and balanced process ventilation

Process ventilation in laboratories at DTU is established as balanced ventilation. This means that heated and filtered air is injected into the laboratories in the same quantity as is sucked out of the building. In balanced ventilation, there is control over air currents, and draught is reduced in the building. The air injection is typically preformed via bags or perforated steel pipes under the ceiling, and is sought to be carried out in a form that does not give rice to draught for the employees.

The ventilation is regulated so there is a minor vacuum in the premises. The vacuum is to prevent that contaminated air from the laboratories gets into the hallways.

If the suction should fail, an overpressure is ensured, to prevent that contaminated air is sucked into the premises from other rooms and installations, i.e. sewages.

Gas trace measurement

The ability of the fume hood to retain hazardous gasses and fumes is controlled by gas trace measurement according to guidelines in the current norm for fume hoods. The results of the individual gas trace measurements are placed in your info box, and must be available for authorities. In the scheme over gas trace measurements, hatch height is stated during work (also marked as physical label), which user disclosed substances the fume hood safety factor is calculated for, and a conclusion regarding the use.
If the info box or the gas trace measurement are not available, then contact Campus Service via the electronic error reporting system.

 

Periodic inspection

Annually, Campus Service inspects the fume hoods and measures the air velocity. See the label on the fume hood.

If the date of the inspection has been exceeded, do not work in the hood - contact Campus Service via the electronic error reporting system.

Safety and surveillance of the system

A control device is installed on fume hoods, ventilated hoods, and local exhausts, to constantly monitor whether the suction is working satisfactory. It looks like a little traffic signal and it gives a visual and acoustic alarm if the suction is not functioning – see user manual in the info box.

In some buildings there is a red and a green control device lamp placed at stairways and/or hallways for surveillance of the system. If the red control lamp is on, then investigate the cause immediately.

Control devices on fume hoods, ventilated hoods, and local exhaust:

Before use, the fume hoods, ventilated hoods and local exhaust must be checked that the suction functions satisfactorily. You can rely on the function, if the green diode on the control device is on. If not, then contact Campus Service via the electronic error reporting system.

Control devices on fume hoods or ventilated hoods

The control device may vary from different suppliers. You can see how your control panel works in the user manual, which should be present in the info box. See an example from Netavent in the right hand menu. Typically, there are following signal lamps:

Green diode (normal):
The fume hood or ventilated hood works optimally. The air velocity is correct.

Yellow diode (wait):
The fume hood or ventilated hood works in terms of safety acceptable, but is approaching the limit, where pollution can penetrate outside the hood. Pull the hatch down further.

Red diode (alarm):
The fume hood or ventilated hood is not functioning safely. Pull the hatch down till the green diode is turned on. If the green lamp fails to turn on, mark the hood with the sign “out of order” and contact Campus Service via the electronic error reporting system. The hood must not be used.

Blue button (accident):
On when forced operation, i.e. extra powerful exhaust is connected. Used for example when spillage of chemicals in the hood. Remove most of the waste, either by drying it or by soaking it in Vermaculite or other absorbent material, which is then collected as chemical waste. Close the hatch all the way down. Turn off "Accident" on the control device when no chemical waste is visible. In order to save energy, it is important to interrupt the forced ventilation, as the hood will run at maximum suction until "Accident" is switched off.

Black button (sound):
Resets the acoustic alarm for 10 min. or 1 hour (depending on settings). Used when e.g. arrangement of equipment in the hood, where a temporary high hatch position (above the gas trace measurement mark) is necessary. No chemicals must be present in the hood.

Malfunction:
Red diode blinks, yellow diode - constant light, bip every 30 sec.
Power failure. Mark the hood with the sign “out of order” and contact Campus Service via the electronic error reporting system. The hood must not be used.

 

Control device for local exhaust:

Green diode (normal):
The local exhaust functions normally. The air volume is correct.

Yellow diode (wait):
The air volume is approaching the border of alert. If the air volume hasn’t adjusted itself to normal pressure within a few sec. the pressure guard will then alert with a red blinking diode and an acoustic alarm. See red diode.

Red diode (alarm):
The local exhaust isn’t functioning safely. In connection with the activated red diode, an acoustic alarm is turned on. Mark the local exhaust with the sign “out of order” and contact Campus Service via the electronic error reporting system. The local exhaust must not be used.

Malfunction:
Red diode blinks, yellow diode is turned on constant, beep every 30 sec.
Power failure. Mark the local exhaust with the sign “out of order” and contact Campus Service via the electronic error reporting system. The local exhaust must not be used.

 

System capacity

The ventilation systems are usually built to cover a capacity of 75%, i.e 75% of all installed process ventilation (fume hoods, ventilated hoods, local exhausts etc.) can be in use at the same time. In teaching laboratories the capacity is typically 100%.

 

Regulation

Many of the systems are made with automatic regulation of the capacity according to actual needs – also known as demand driven ventilation. The volume of air from a fume hood is regulated by a sensor that seeks an air velocity in the hatch of 0.5 m/s. This means that the extracted volume of air depends on the height of the hatch opening.

The hatch opening must be as small as possible during work. A fume hood that is left with the hatch in an upper position overnight, uses an unnecessary amount of energy.

In many laboratories central sensors are set up that record the activity in the rooms. If there is no personal activity in a room, the air velocity in the hatch opening is reduced to 0.3 m/s to save energy.

 

Sewage suction

On Campus in Lyngby there is an exhaust on all chemical sewers. This extraction must prevent the suction of air from the sewer, if there is a vacuum in the room and the water trap is empty. Near to the ceiling door, in the ventilation room on the second floor, a green lamp is turned on when the sewer suction runs.

As an added safety against replenishing air from the sewer, it is recommended that all water locks and floor drains be replenished with water once per month.

 

Malfunction

If the ventilation system fails, then contact Campus Service via the electronic error reporting system.