How X-Ray Baggage Scanners Work: Colour Coding, Material Discrimination & Operator Training

X-ray baggage scanners are a frontline defence at courthouses, government offices, hotels, and airports across Bangladesh. Yet most security managers know surprisingly little about how these machines actually work. Understanding the technology behind them helps you select the right equipment, train your operators effectively, and get maximum detection capability from your investment.

This guide explains the complete picture: from the physics of dual-energy X-ray to the colour coding that operators interpret on screen, tunnel sizing, throughput rates, and the training standards that separate a professional screening operation from a checkbox exercise.

The Physics: How X-Ray Penetrates Baggage

An X-ray baggage scanner generates a focused beam of electromagnetic radiation at high voltage — typically between 140 kV and 160 kV for standard units. This beam passes through objects placed on the conveyor belt. Different materials absorb X-rays at different rates, and the detector array on the far side of the tunnel measures how much radiation passes through each point.

Dense, heavy materials such as metals absorb more X-rays and appear darker on the image. Lighter organic materials such as food, paper, explosives, and narcotics absorb fewer X-rays and appear lighter. The scanner's software converts these absorption differences into a colour-coded image the operator reads in real time.

The key variable is atomic number (Z). Materials with a low Z value — organics like carbon-based explosives, drugs, and plastics — interact with X-rays differently from high-Z materials like lead and steel. This difference is the foundation of material discrimination.

Dual-Energy X-Ray: The Technology Behind Material Discrimination

Standard single-energy X-ray shows you an image, but it cannot reliably tell you what a material is made of. Dual-energy X-ray solves this by generating two separate X-ray beams at different energy levels simultaneously — typically a high-energy beam and a low-energy beam.

Each material interacts differently with the two energy levels. By comparing how much of each beam passes through an object, the system calculates its effective atomic number. This Z-number maps to a material category. The processor assigns a colour to each pixel based on this calculation, giving the operator an immediate visual classification of every object in the bag.

Modern dual-energy systems can distinguish between:

Organic materials (low Z: explosives, drugs, food, paper, plastic)
Inorganic materials (high Z: metals, ceramics, glass)
Mixed materials (mid-range Z: alloys, some composites)

This discrimination is far more powerful than visual shape recognition alone. A block of plastic explosive inside a book looks very different on a dual-energy system than it does on a single-energy machine.

The Colour Coding System: What Each Colour Means

Every X-ray scanner manufacturer uses a standardised colour scheme. Operators must learn this scheme instinctively, because they typically have 2–4 seconds to assess each bag before it exits the tunnel.

Orange: Organic Materials

Orange indicates low-Z organic material. This category includes food, paper, wood, fabric, and — critically — most explosives and narcotics. When operators see dense orange areas of unusual shape, they should investigate further. A folded garment appearing orange is expected. A dense, regular orange rectangle in a bag that should contain only electronics is a red flag.

Blue: Inorganic Materials

Blue indicates high-Z inorganic material. Metals, ceramics, and glass appear in shades of blue. A metal water bottle appearing blue is entirely expected. An unexpected blue mass concealed beneath other items — particularly one with an unusual profile — warrants a secondary inspection.

Green: Mixed-Composition Materials

Green indicates materials with mid-range atomic numbers — things that are neither clearly organic nor clearly inorganic. Many manufactured goods fall into this category. Batteries, circuit boards, and certain polymers commonly appear green. Operators learn the typical green signatures of common items and flag those that deviate.

Black: Total X-Ray Absorption

Black areas represent objects so dense that the X-ray beam cannot penetrate them. Thick steel components and lead items appear black. Operators should note the shape and context of black areas — a lead-lined compartment hidden inside an otherwise transparent bag is a serious indicator.

Colour Inversion and Enhancement Tools

Professional scanners include image enhancement tools that operators use during secondary review. These include high-penetration mode (reveals detail inside dense objects), organic stripping (removes organic material from the image to reveal hidden inorganic items), and inorganic stripping (the reverse). These tools are not used for every bag — only when the operator's initial assessment raises questions.

Tunnel Sizes: Matching the Machine to Your Throughput

Selecting the wrong tunnel size is one of the most common procurement mistakes. A tunnel too small slows your queue and forces guards to manually remove items. A tunnel too large wastes budget on capability you do not need.

Standard Tunnel: 100 cm × 80 cm (W × H)

This is the most common size for court buildings, office lobbies, hotels, and government facilities in Bangladesh. It handles briefcases, laptop bags, handbags, and small backpacks comfortably. Most international carry-on luggage fits through a 100×80 cm aperture. This size accommodates approximately 15–20 bags per minute at standard conveyor speeds.

Medium Tunnel: 140 cm × 100 cm (W × H)

This size suits logistics hubs, port facilities, and large government complexes where checked-luggage-sized bags and parcels are screened. It handles larger backpacks and multiple items placed side by side, improving throughput at high-volume checkpoints.

Oversized Tunnel: 180 cm × 150 cm (W × H)

Oversized tunnels are for cargo screening, freight terminals, and port environments where pallets, large boxes, and industrial packages must be X-rayed. These units require significantly higher generator power (typically 320 kV or above) and specialised operator training for cargo interpretation. Customs authorities and export processing zones in Bangladesh increasingly use oversized tunnels for export cargo verification.

Throughput Rates: Planning Your Security Queue

Throughput directly determines how many lanes you need and how long your security queue will be at peak hours.

A standard 100×80 cm scanner with a conveyor speed of 0.2 m/s processes approximately 15–20 bags per minute under ideal conditions. Real-world throughput is lower because:

Passengers take time to remove laptops, belts, and shoes
Operators pause the belt when they spot items requiring further review
Secondary screening removes one officer from primary duties

For planning purposes, use 12 bags per minute as your operational throughput for a standard scanner with one trained operator. For a facility expecting 500 visitors in a 2-hour peak period, you need at least 2 scanner lanes plus a secondary screening area.

High-volume facilities — such as the main entrance of Dhaka's High Court or a major government ministry during public hours — typically operate 3 to 4 lanes during peak periods. Oversizing your checkpoint for peak capacity prevents bottlenecks that compromise security by rushing operators.

Generator Voltage and Detection Performance

The generator voltage directly affects how well the scanner penetrates dense items and how clearly it renders detail. Higher voltage means better penetration but requires more shielding and power draw.

For standard checkpoint applications, a 160 kV generator provides excellent performance for mixed bag contents. For cargo and freight applications where dense pallets are screened, generators of 320 kV or 450 kV are standard. The resolution specification — measured by the smallest wire gauge the scanner can detect — should be 0.1 mm wire diameter or better for a professional security checkpoint. Lower-cost scanners with 0.2 mm or 0.3 mm resolution miss fine wires and thin blades.

Operator Training: The Human Factor in X-Ray Screening

The best scanner on the market produces zero security value if the operator does not know how to interpret the image. Research consistently shows that operator performance degrades significantly after 20–30 minutes of continuous screening. This is called the vigilance decrement, and it is why professional security operations rotate operators every 20 minutes.

Core Training Curriculum

Every X-ray operator must complete training covering:

Image interpretation fundamentals — colour coding, material discrimination, shadow effects
Threat item recognition — firearms, bladed weapons, improvised explosive device components, narcotics packaging
Prohibited and restricted items — context-specific to your facility's rules
Operator interface — image enhancement tools, how to call for secondary screening
Security procedures — what to do when a threat item is detected, escalation protocols

Threat Image Projection (TIP)

Advanced X-ray systems include a Threat Image Projection feature. The system randomly superimposes images of known threat items onto real bag scans. The operator does not know which bags contain projected images. Their detection rate and false-alarm rate on TIP images are logged automatically, providing objective performance data for supervisors.

TIP training is mandatory at international airports and is increasingly adopted by major corporate campuses and government facilities. We strongly recommend specifying TIP capability when procuring scanners for any high-security application in Bangladesh.

Certification Requirements

Operators should receive a minimum of 40 hours of initial training before operating independently. This includes classroom instruction, simulator exercises, and supervised live screening. Refresher training should occur every 6 months. Annual certification testing — where operators must meet a defined detection rate threshold — keeps skills sharp and provides documentation of professional standards.

In Bangladesh, there is currently no mandatory national certification standard for X-ray operators outside of aviation. However, leading organisations align their training programmes with the ICAO Doc 8973 aviation security training standard as a benchmark for best practice.

Leading Brands: Astrophysics, Smiths Detection & UVScan

Selecting a reputable brand ensures consistent image quality, reliable calibration, and access to spare parts and technical support in Bangladesh.

Astrophysics produces the widely deployed XIS series, popular across South and Southeast Asia for its reliable dual-energy performance and competitive total cost of ownership. The XIS-6550 (65×50 cm tunnel) suits small office checkpoints; the XIS-100100 suits high-volume government facilities.

Smiths Detection (now part of Smiths Group) manufactures the HI-SCAN series, which is the international airport standard in many countries. The HI-SCAN 100100T is a benchmark product for large-aperture security screening with exceptional resolution. Smiths Detection systems support TIP and integrate with security management platforms.

UVScan offers strong mid-range options that have gained traction in the Bangladeshi market for their price-to-performance ratio, particularly for hotel lobbies, private corporate campuses, and educational institutions.

When evaluating any brand, verify that the system carries a CE marking and complies with IEC 60950 (electrical safety) and applicable radiation safety standards. In Bangladesh, the Bangladesh Atomic Energy Regulatory Authority (BAERA) governs the use of radiation-emitting equipment including X-ray scanners. Ensure your supplier provides BAERA-compliant documentation.

Bangladesh Context: Where X-Ray Scanners Are Deployed

X-ray baggage screening has become standard at a growing number of facilities across Bangladesh:

Courts and Judicial Buildings: The Bangladesh Supreme Court and major district courts use baggage scanners at all public entrances. High footfall and the presence of sensitive proceedings make these mandatory installations.

Government Ministry Buildings: Key ministries in Dhaka's government district screen all visitor bags. Many government buildings upgraded their scanners following security reviews conducted between 2022 and 2025.

International Hotels: Five-star hotels in Dhaka — including major chains along Gulshan and Banani — screen all vehicles and pedestrians entering the property. Hotel operators face reputational liability if a security incident occurs in their premises.

Hospitals and Healthcare: Leading private hospitals in Dhaka increasingly deploy scanners at main entrances to manage patient and visitor safety.

Banks and Financial Institutions: Bangladesh Bank's ICT Security Guideline v4.0 does not directly mandate X-ray scanning, but physical security addenda for bank branches in risk-elevated zones commonly specify scanner deployment.

Maintenance and Calibration

An X-ray scanner is a radiation-emitting instrument. It requires scheduled calibration to maintain accurate material discrimination and image quality. Calibration should occur:

Daily: Operator-level image quality check using a calibration test object provided by the manufacturer
Quarterly: Technician-level calibration using certified phantoms to verify Z-number accuracy
Annually: Full service including X-ray tube inspection, conveyor belt and roller inspection, and lead curtain replacement if worn

Maintain a calibration logbook. FSCD and other regulatory inspectors may request evidence of maintenance during facility audits.

Get Expert Help

Selecting and deploying an X-ray baggage scanner requires matching the equipment specification to your facility's threat level, throughput demand, and regulatory environment. SSAL has deployed X-ray scanning solutions across courts, government buildings, hotels, banks, and industrial facilities throughout Bangladesh.

Our team handles the full project — from threat assessment and specification design to supply, installation, BAERA documentation support, and operator training. We work with leading brands including Astrophysics and Smiths Detection to ensure you receive a solution that meets international performance standards.

Talk to Our Expert — contact SSAL today for a free site assessment and checkpoint design consultation.