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:

With the following definitions:

1	Item Malfunction	Failure or unintended behaviour of an item with respect to its design intent	ISO 26262
2	System Failure	System level functional failure leading to a VLH	Dictionary
3	Vehicle Level Hazard	Potential source of harm caused by an Item Malfunction	ISO 26262
4	Hazardous Event	Combination of a hazard and an Operation Situation	ISO 26262
5	Incident/Accident	Undesirable, incidental, and unplanned event directly causing unintentional injury or harm	Dictionary
6	Harm	Physical injury or damage to the health of persons	ISO 26262

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

No.	Item Malfunction	System Failure	Vehicle Level Hazard	Hazardous Event	Incident/Accident	Harm
1	Brake pedal sensor malfunction	No braking demand detection	Loss of braking	Happens at a crossing	Crash with coming car	Crash injuries
2	Battery voltage sensor malfunction	Overcharge	Thermal incident	any situation	Vehicle fire	Burns, intoxication
3	Front light command malfunction	No illumination demand detection	Loss of forward illumination	at night on an unlit road	Crash onto a tree	Crash 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:

• 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 word	Hazard description (ACCELERATION)	Hazard description (BRAKING)	Hazard description (STEERING)
0	NOT	No acceleration	No braking	No yaw angle correction
1	MORE	Excessive acceleration	Excessive braking	Excessive yaw angle correction
2	LESS	Insufficient acceleration	Insufficient braking	Insufficient yaw angle correction
3	AS WELL AS	Fluctuations in acceleration	Fluctuations in braking	Fluctuations in yaw angle
4	REVERSE	Braking instead	Accelerating instead	Opposite yaw angle correction
5	EARLY	Provide acceleration before required	Provide braking before required	Yaw angle correction provided before required
6	LATE	Provide acceleration after required	Provide braking after required	Yaw angle correction provided after required
7	UNINTENDED	Unintended acceleration	Unintended braking	Unintended yaw angle correction

Non Motion-related Vehicle Level Hazards

No.	Vehicle Level Hazard	Description
0	Pressure burst	Critical 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.
1	Parts disconnection	Disconnection 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 incident	Heating 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
3	Toxic gases release	Release of a toxic compound that can be inhaled or touched by the customer. May lead to viscera harm
4	Irritant release	Release of irritants out of containers. May lead to chemical burns harm
5	Electrical energizing	Electrical energizing of the vehicle parts that may lead to electrical shock and electrical burns harm
6	Electrical heating	Electrical heating hazard that may lead to burns harm. May lead to hazardous event – explosion due to release of thermal energy
7	Electrical arcing	Arcing due to an electrical discharge through the air

VLH Nomenclature

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

VLH

–

Symbol 1

M

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;