Recommendations on ISO 26262 Hazards Analysis Procedure

Introduction

As defined in ISO 26262-3 clause 6.4.2.2 the hazards shall be determined systematically based on possible malfunctioning behaviour of the item.
These hazards are essentially vehicle level hazards which in combination with operational situations give exact hazardous event that will be the assessed within risk assessment procedure.

As defined in ISO 26262-3 HAZOP is suitable to support hazard identification at the item level and then it can be supported by brainstorming, checklists, quality history, and field studies to get to the vehicle level effects and hazards (VLH).

A VLH is defined as per the ISO 26262 as being a potential source of harm, and appears in the event chain as follows:

image2018-9-25_9-12-12.png

With the following definitions:

1Item MalfunctionFailure or unintended behaviour of an item with respect to its design intentISO 26262
2System FailureSystem level functional failure leading to a VLHDictionary
3Vehicle Level HazardPotential source of harm caused by an Item MalfunctionISO 26262
4Hazardous EventCombination of a hazard and an Operation SituationISO 26262
5Incident/AccidentUndesirable, incidental, and unplanned event directly causing unintentional injury or harmDictionary
6HarmPhysical injury or damage to the health of personsISO 26262

Examples relating to the above definition are mentioned in the chart below:

No.Item MalfunctionSystem FailureVehicle Level HazardHazardous EventIncident/AccidentHarm
1Brake pedal sensor malfunctionNo braking demand detectionLoss of brakingHappens at a crossingCrash with coming carCrash injuries
2Battery voltage sensor malfunctionOverchargeThermal incidentany situationVehicle fireBurns, intoxication
3Front light command malfunctionNo illumination demand detectionLoss of forward illuminationat night on an unlit roadCrash onto a treeCrash injuries

This post references the typical identified VLHs that can harm directly vehicle occupants and other road traffic participants including pedestrians and cyclists.

A VLH is a direct source of harm inducing a direct exposure to the:

  • vehicle occupants;
  • road traffic participants;
  • pedestrians;
  • cyclists.

The VLHs shall be defined in terms of the conditions or behavior that can be observed at the vehicle level so basically they can be divided into 2 main groups:

  • VLHs from the loss of the vehicle control while in motion (motion-related)
  • VLHs that are not related to the loss of the motion control (non motion-related)

Vehicle Level Hazards

HAZOP

Hazard identification can be accomplished through various hazard analysis techniques. The hazards shall be determined systematically by using adequate techniques. Regarding the existing methodologies and techniques for the hazards analysis it is considered to do hazard analysis through HAZOP methodology described in IEC 61882. HAZOP is an exploratory type of analysis where applicable guide words are applied to each of the functions of an item to postulate malfunctioning behaviors. HAZOP facilitates a structured and systematic examination of the operation of the item within the vehicle. It may be used to identify and evaluate malfunctioning behaviors of an item that could lead to hazards that create the potential for harm to the occupants of the subject vehicle, to other vehicles and their occupants, or other persons at risk such as pedestrians, pedal cyclists in the vicinity of the subject vehicle or maintenance personnel.

Within HAZOP the analyst assumes there are functions defined during item definition phase and in order to identify deviations applies (systematically) a set of Guide Words to each function. The Guide words are chosen based on idea they shall be appropriate to the study and neither too specific (limiting ideas and discussion) nor too general (allowing loss of focus). As an example the following list of the guide words might be used.

Motion-related Vehicle Level Hazards

The 6 degrees of motion freedom of a solid body are the following:

6 degrees of freedom representation
  • Longitudinal
  • Lateral
  • Vertical
  • Yaw
  • Pitch
  • Roll

All of these degrees of freedom shall be taken into account while identifying VLHs. The VLHs identified can be represented as in the following table

No.Guide wordHazard description (ACCELERATION)Hazard description (BRAKING)Hazard description (STEERING)
0NOTNo acceleration No brakingNo yaw angle correction
1MOREExcessive accelerationExcessive brakingExcessive yaw angle correction
2LESSInsufficient accelerationInsufficient brakingInsufficient yaw angle correction
3AS WELL ASFluctuations in accelerationFluctuations in brakingFluctuations in yaw angle
4REVERSEBraking insteadAccelerating insteadOpposite yaw angle correction
5EARLYProvide acceleration before requiredProvide braking before requiredYaw angle correction provided before required
6LATEProvide acceleration after requiredProvide braking after requiredYaw angle correction provided after required
7UNINTENDEDUnintended accelerationUnintended brakingUnintended yaw angle correction

Non Motion-related Vehicle Level Hazards

No.Vehicle Level HazardDescription
0Pressure burstCritical pressure increase that may lead to pedestrians/cyclists/other drivers hitting (by the vehicle parts) harm. May lead to hazardous events due to release of potential energy
– burst;
– flying parts;
– pressure waves.
1Parts disconnectionDisconnection of pats of the vehicle that may lead to pedestrians/cyclists/other drivers hitting harm In case of disconnection inside the cabin may lead to the vehicle occupants hitting harm
2 Thermal incidentHeating of vehicle parts due to radiated energy, convective energy, conducted energy transmission to that parts. Different from electrical heating related to the Joule effect. May lead to burns harm. May lead to hazardous event – explosion due to release of thermal energy
3Toxic gases releaseRelease of a toxic compound that can be inhaled or touched by the customer. May lead to viscera harm
4Irritant releaseRelease of irritants out of containers. May lead to chemical burns harm
5Electrical energizingElectrical energizing of the vehicle parts that may lead to electrical shock and electrical burns harm
6Electrical heatingElectrical heating hazard that may lead to burns harm. May lead to hazardous event – explosion due to release of thermal energy
7Electrical arcingArcing due to an electrical discharge through the air

VLH Nomenclature

The following nomenclature (scheme) might be used to classify hazards with the keys.

VLHSymbol 1M
Symbol 3
number

1st sequence of letters:

VLH: Vehicle Level Hazard

2nd sequence of letters:

Symbol 1:

  • F: forward motion;
  • R: reverse motion;
  • Y: yaw motion;
  • S: standstill;
  • N: non-motion related.

Symbol 3:

  • For Motion related hazards:
    • A: Accelerating
    • B: Braking
    • X: not applicable
  • For NON-Motion related hazards:
    • M: mechanical hazard;
    • E: electrical hazard;
    • T: thermal hazard;
    • C: chemical hazard;

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