Baggage screening processes

The Hold Baggage Screening process can be subdivided into a number of levels. Level 1 screening of bags is carried out automatically by a screening machine. This is basically a pre-sortation to determine whether a bag is potentially suspect.
At Level 2, the machine-generated images of uncleared bags are examined by trained operators or processed automatically by a Level 2 machine. The small fraction of uncleared bags remaining after this level is routed to a Level 3 machine. Here, trained operators examine the detailed images of these bags.

Bags that are still not cleared after Level 3 examination are investigated manually in the presence of their owners (Level 4). Bags that are not cleared at Level 4 become suspect bags. Regulations determine how these will further be dealt with (Level 5).

Table 1 Levels of BHS

Fig.1. System design

X-ray scanning procedure works on principle of penetrating X-rays on bag or luggage to be detected. X-ray scan distinguishes objects by their atomic number and classifies by colour.

XBIS contains following major sub assemblies: X-ray generator, X-ray sensor amplifier PCB, Computer with software, Tunnel with a conveyor mechanism through which the baggage passes through Image processing software with display and keyboard

Fig 1: X-ray baggage inspection system

Fig 2: Baggage seen on screen

Working Principle:

XBIS is a compact system utilizing X-rays for the quick and efficient examination of handbags, parcels, suitcases, letters, books, etc. The unit is equipped with conveyor belt, which transports the luggage through the inspection tunnel. An X-ray generator supplies required radiation during screening. The emitted X-rays penetrate through the object under examination, which, while passing through the unit, screen luggage piece slice by slice. The obtained picture information is then stored electronically and is processed to get a clear, informative image, which is finally reproduced on monitor screen.

Theory Of Operation:

All items to be inspected must be placed on the conveyor belt and the power is switched ON, then the items are transported to the inspection chamber. The items are placed flat in the center of the belt. They are so placed that even the smallest items can be inspected side by side if it is necessary. It is recommended that the leading edge of the conveyor break the sensor beam clearly. As the items reach the inspection chamber X-rays are automatically switched ON and image forming process begins and the inner objects of the luggage are displayed on the monitor.

In image forming process, the object is screened line by line as it moves on the conveyor belt. After the X-rays pass through the item to be inspected they strike a detector, which splits each line into more than 500 picture elements (pixels). This picture information is electronically processed, stored and finally reproduced on the monitor screen. The picture scrolls across the monitor as the item is being scanned. Image examination may be facilitated in any of 9 freely selectable image sections on the entire picture.

Imaging Sequence:

While system is idle, the scan engine is always running and collecting detector signals without X-rays. This signal is called dark current. Conveyor moves and brings baggage into the tunnel. Baggage blocks LS1 and software turns on X- rays. After a delay to ensure X-ray generator is fully up, software begins to collect data for full signal. This is called light current. After light current is collected software will calculate correcting factor for each channel. This whole process of dark current, light current and correcting factor is called calibration. When baggage reaches LS2, system begins to make an image. If calibration is incomplete, system will use previous calibration. At next time, system will continue light current collection.

Fig 4: Imaging Sequence

After baggage passes LS2 a certain distance, software will stop generating image, but still keeps X-rays ON. If during the time X-rays are still ON, if new baggage reaches LS1, system will continue image processing without recalibration. This is done to prevent turning X-ray generator ON and OFF frequently to prolong its life. After some extra delay, if there is no other baggage entering tunnel, system urns off X-rays. To ensure X-rays are off, system begins dark current collection.

Image Representation: Automatic exposure allows the operator to totally concentrate on the representation in interpretation of X-ray image. The picture quality and clarity helps the operator in making decision of whether the contents are safe or suspicious. The success of screening operation is dependent upon interpretation of image by the operator. The multi energy system distinguishes between materials according to their atomic numbers. The colors, which are displayed on monitor based on atomic numbers, are shown in the Table 2.

X-Ray Protection:

Considerable efforts have been made to ensure operator and equipment safety. XBIS is configured so that it provides reliable protection against hazardous radiation during operational mode. System employs extremely low X- ray dose and is designed in such a way that radiation is emitted only when object is transported. This equipment contains a set of lead-curtains on both entry and exit sides and an extensive lead shielding guarantees that radiation leakage and scatter practically zero. This way, X-rays will endanger neither passenger nor inspection personal even after numerous inspections. Several electronic safety circuits guarantee that radiation is immediately cut off in case inadmissible deviations from preset values are registered.

Table 2 Different atomic numbers and their properties

Advantages of the XBIS System:

1. Screening the contents of the luggage without opening the bag. 


2. Faster way of luggage screening. 


3. The screening is done in a much reduced amount of 
time as compared to that manually. 


4. The system is designed to provide both high through 
put and provide and detailed examination of carry on luggage and other articles by non-technical operating personal. 


5. It is advantageous because it does not produce any radiation dosage threat to the operating personnel. 


Disadvantages of the XBIS System:

1. A tamed pack of bag full of iron, heavy metal will look totally black from which the illegal materials are difficult to be detected.

2. There may be shock hazards,which may prove fatal.

Date: 2016-04-22; view: 1348