Seat Belt Examinations
Seat Belt Examinations
Seat Belt Examinations

 

 

Introduction

Highlighted terminology is explained at the bottom of the page.

 

We are experienced in the examination of safety belts for vehicle occupant usage in both low and high-speed collisions.

It is vitally important for our clients in litigation to determine whether the active restraints were both operational, i.e. free from defect, and were utilised correctly by a vehicle occupant during a collision.

The examination of safety belts to determine usage is by no means as simple as a quick look. While there is sometimes obvious evidence to determine their usage conclusively, there are many occasions when only less subtle evidence is present.

Safety belt examinations for evidence of usage are primarily restricted for moderate to severe collisions, where significant levels of decelerations are generated. During a collision when a safety belt restrains a vehicle occupant, certain engagements between the component parts create characteristic witness marks due to the high loading forces at their contacting points. This loading creates physical evidence that we can identify during an examination long after the event.

We perform detailed examinations to both identify and analyse these witness marks and is often able to establish conclusively whether or not safety belts were in use during a collision.

These investigative techniques provide important objective analysis for our clients involved in high-value litigations.

As a result of our examinations, we provide the following conclusions:

  1. Conclusive Usage - The vehicle occupant was correctly utilising the safety belt.
  2. Conclusive No Usage - The vehicle occupant was not utilising the safety belt.
  3. Inconclusive Usage - Insufficient physical evidence to determine safety belt usage by the vehicle occupant.

 

 

examination techniques

We inspect the component parts of safety belt systems for webbing friction burns, webbing abrasions, roping, roping and thread cuts, thread disruptions, webbing creases, dislodged stay buttons, trim abrasions, clothing or plastic transfers, body fluid, laterally loaded anchorage, retractor activation and any other relevant witness marks.

If the webbing of a safety belt is locked stowed, then it is most likely conclusive evidence that it was not in use at the time of a collision. However, there are occasions where safety belts have been worn, released and spooled back into the retractor. Then during the process of occupant extraction by the emergency services, the structural integrity of the B or C-pillar has been compromised and effectively crimped and locked the now retracted webbing taught in the stowed position. Where required, we can strip down the components parts to identify other evidence to confirm the safety belt's usage.

If the webbing of a safety belt is locked extended from the retractor, then it is highly likely conclusive evidence that it was in use at the time of the collision. However, as modern vehicles emit a warning noise to the vehicle occupants should it detect a load on a seat without the safety belt being engaged, some vehicle occupants route the webbing around the back of the seat or across its front, with the latch plate entered into the buckle without forming any restraint. If the tongue is then disengaged from the buckle it can give the appearance of being locked out, but often further examination techniques confirm it was not correctly used. Furthermore, there are fake buckles available for purchase on the internet that have their own latch plate that enters into the vehicle’s buckle and stops the warning noise.

If an examination requires more invasive techniques, we remove the entire system for a detailed forensic analysis of the component parts.

Where required, we use both stereo microscopy and digital macro/micro photography to examine and record the components of the system.

Ordinarily, in high-speed collisions, there tends to be more considerable evidence to determine usage. However, it is essential to understand that even in high-speed collisions, not all webbings lock taught, either in the stowed or extended position.

It is important to note that some components of a safety belt system may have been replaced due to historical collisions. Furthermore, a safety belt system may not have been reset from a previous deployment prior to the collision under investigation occurring. During our examinations we consider all potential scenarios.

 

 

operational system

When a safety belt is fastened or unfastened, the latch plate sliding along the webbing is inserted into or removed from the buckle. The buckle is anchored to the vehicle floor and is designed to hold the latch plate firmly while allowing the safety belt to be fastened and unfastened with very little force. In an emergency, it is designed so that another person can easily remove the latch plate from the buckle and free the vehicle occupant.

There is a multitude of safety belts fitted to modern vehicles; for example, two-point, lap, sash, three-point, belt-in-seat (BIS), 4 5 6 or 7 points.

The shoulder guide loop is an oval guide allowing the webbing to travel between the retractor in the base of the pillar, through the latch plate and back over to the anchorage point near the base of the pillar housing the retractor. The shoulder guide loop is often referred to as a D ring due to its oval shape, the pillar loop or webbing guide. The shoulder guide loop is made of metal with a plastic coating and is semi-fixed to the pillar, allowing a limited range of movements for occupant comfort.

Webbing is the part of the safety belt in contact with the vehicle occupant that receives and softens the loading of an impact. Webbings are composed of polyester or nylon material, with polyester having the higher coefficient of friction compared to nylon. They are woven from about 300 warp strands and one weft strand. With a webbing width of approximately 48 mm, they have an approximate three metric ton tensile strength. The webbing that passes across the lap of the occupant is referred to as the lap strap and where it passes across the occupant’s shoulder and chest it is referred to as the diagonal or sash strap. When the safety belt is used correctly, it forms a loop around the seat occupant and successfully restrains them when they are subject to deceleration forces.

The retractor is a winding mechanism allowing the safety belt webbing to be withdrawn and brought back into its housing. It also serves to lock the webbing in place in the event of a collision, thereby helping to restrain the vehicle occupant. The retractor is usually installed either in the pillar section of the motor vehicle or the seat. It has two sensors, one sensor locks the safety belt webbing when the vehicle decelerates quickly or accelerates faster than a certain speed and the second sensor locks the extraction of webbing when it is pulled out at a quicker rate than normal movement. There is a multitude of different retractors fitted to modern vehicles.

 

Fees & Lead Times

Our service level agreements for fees and lead times for our seat belt examination service vary due to the complexity of each case and any additional investigative services required.

This service is part of our all-inclusive investigative reconstruction package.

Please contact us to discuss your requirements.

 

Terminology

Active Restraint – A restraint system that relies on the action of its user.

Adult Safety Belt – An approved webbing used to restrain adults.

Anchorage – Provision to transfer forces applied to the seat belt assembly to the structure of the vehicle.

Body Fluid – Those liquids originating from inside the bodies of living species.

Buckle and Latch Plate – A quick release connector which fastens the belt assembly into a loop.

Conclusive Usage – The vehicle occupant was correctly utilising the safety belt.

Conclusive No Usage – The vehicle occupant was not utilising the safety belt.

Inconclusive Usage – Insufficient physical evidence to determine safety belt usage by the vehicle occupant.

Lap Strap – The part of the loop that passes across the lap of the seat occupant.

Locked Stowed – A safety belt where the webbing is firmly locked in its default stowed location.

Locked Extended – A safety belt where the webbing is firmly locked out having been partially spooled out from the retractor.

Loop – A complete seat belt assembly as it would be installed around the seat occupant.

Retractor – A device for storing all or part of the strap material of a seat belt assembly.

Safety Belt - An arrangement of straps with a securing buckle, adjusting devices and attachments which is capable of being anchored to the interior of a power-driven vehicle and is designed to diminish the risk of injury to its wearer, in the event of collision or of abrupt deceleration of the vehicle, by limiting the mobility of the wearer's body. (United Nations, 2008)

Sash Strap – The part of the loop that passes across the chest and shoulder of the seat occupant.

Seat Belt Assembly – Belt, including a buckle, length adjustor, retractor, and means for securing to an anchorage, that fastens across the pelvic area to provide pelvic restraining during operation and roll-over collisions.

Shoulder Guide Loop - An oval guide allowing the webbing to travel between the retractor in the base of the pillar, through the latch plate and back over to the anchorage point near the base of the pillar housing the retractor.

Strap – A flexible component of webbing designed to transmit forces.

Vehicle Occupant – Road user in or on a vehicle.

Witness Mark – A mark providing contrast against its surrounding surface that serves as an indicator of interaction.

 

our Services

All Inclusive Service Collision Accident

All-Inclusive Investigation
Consultancy

Consultancy
Collision Reconstruction Collision Accident

Investigative Reconstructions
Desktop Analysis Collision Accident

Desktop Analysis
Claim Validation

Claim Validations
Vehicle Examinations Collision Accident

Vehicle Examinations
Laser Scanning Collision Accident

3D Laser Scanning
Forensic Animations Collision Accident

Forensic Animations
CCTV Digital Video Analysis Collision Accident

Digital Video Analysis
Collision Site Analysis Collision Accident

Collision Site Analysis
UAV Collision Accident

UAV Aerial Imagery
Collision Accident Computer Simulations

Computer Simulations
Collision Accident Vehicle Forensics Infortainment

Vehicle Forensics
Collision Accident Crash Data Analysis

Crash Data Analysis
Collision Accident Light Bulb Analysis

Lamp Analysis
Collision Accident Seat Belts

Seat Belt Examinations
Incident Analysis

Incident Analysis
Collision Accident Photography

Site Photography
Collision Accident Scale Plan

Scale Plans
Collision Accident Report Validation

Report Confirmations
Research

Research