Safety Risk Categorization

Definitions

Safety Risk Categorization

the safety work product that categorizes the safety risks associated with accidents and hazardsin terms of accident hazard indicies and safety assurance level

Accident Hazard Indices (AHI)

a category of accidents/hazards associated with a single combination of accident/hazard severity level and accident/hazard frequency level

Safety Assurance Levels (SAL)

a category of hazard indicies that represent roughly the same level of safety risk

Classification

As illustrated in the preceding figure, Safety Risk Categorization is part of the following inheritance hierarchy:

• Type: Concrete
• Superclass: Document
• Subclasses:
  • None

Responsibilities

The typical responsibilities of a Safety Risk Categorization are to:

• Define useful categories of safety risks.
• Support hazard and safety risk analysis.
• Promote communication about safety.
• Set safety policy (e.g., mandatory reporting)

Contents

The typical contents of the safety risk categorization are:

• Accident severity category
• Associated range of negative impact (harm)

Stakeholders

The typical stakeholders of the safety risk categorization are:

• Producer:
  • Safety Team
• Evaluators:
  • Safety Evaluation Team
• Approvers:
  • Project Management Team
  • Customer Representative
• Maintainers:
  • Safety Team
• Users:
  • Safety Team, which uses the hazard indices and safety assurance levels to produce safety evidence assurance levels (SEALs).

Phases

• Business Strategy: Not Applicable
• Business Optimization: Not Applicable
• Initiation: Completed
• Construction: Maintained
• Delivery: Maintained
• Usage: Maintained
• Retirement: Archived

Preconditions

The accident severity categorization typically can be started if the following preconditions hold:

• The initiation phase is started.
• The safety team is adequately staffed and trained in safety program planning.

Inputs

The safety risk categorization typically has the following inputs:

• Work Products:
  • Safety Program Plan
  • Accident Frequency Categorization
  • Accident Severity Categorization
• Stakeholders:
  • Customer Representatives
  • Safety Domain Experts

Guidelines

• Start with an safety risk categorization from some international standard.
• Modify it to meet the needs of the endeavor.
• Group accident hazard indices (AHIs) into safety assurance levels (SALs) of roughly the same level of risk.

Conventions

The safety risk categorization is typically constrained by the following conventions:

• Content and Format Standard
• MS Word Template
• XML DTD
• Evaluation Checklist

Examples

As illustrated by the following example tables, the number and definitions of accident hazard indices and safety assurance levels varies by application domain and international standards. Example safety risk categorization tables from various international standards include:

• Medical Equipment
• Railways
• United Kingdom Ministry of Defense
• United States Department of Defence

Medical Equipment

The International Electrotechnical Commission (IEC) standard, Medical Electrical Equipment - Part 1: General Requirements for Safety (IEC 601-1-4: 1996), defines accident hazard indices and safety assurance levels as follows:

The International Electrotechnical Commission (IEC) standard thus categorizes the 24 accident hazard indices (AHIs) into the following three safety assurance levels (SALs) for dealing with safety risks:

Railways

The European Community standard, Railway Applications: Software for Railway Control and Protection Systems (CENELEC EN 50128: 1997), defines accident hazard indices and safety assurance levels as follows:

The European Community railway standard thus categorizes the 24 accident hazard indices (AHIs) into the following five safety assurance levels (SALs) for dealing with safety risks:

United Kingdom Ministry of Defense

The United Kingdom Ministry of Defense military standard, Safety Management Requirements for Defence Systems Containing Programmable Electronics: Part 1 - Requirements (DEF STAN 00-56 (Part 1)/Issue 2: 1996), defines accident hazard indices and safety assurance levels as follows:

Example accident severity categorization tables, adapted from:

The United Kingdom Ministry of Defense military standard thus categorizes the 24 accident hazard indices (AHIs) into the following four safety assurance levels (SALs) for dealing with safety risks:

United States Department of Defence

The US Department of Defense military standard, Mishap Risk Management (MIL-STD-882D: 1998), uses accident frequency levels to define accident hazard indices and safety assurance levels as follows:

The US Department of Defense military standard thus categorizes the 20 accident hazard indices (AHIs) into the following four safety assurance levels (SALs) for dealing with safety risks:

For software safety risk, the US Department of Defense military standard, Mishap Risk Management (MIL-STD-882D: 1998), uses software control categories to define accident hazard indices and safety assurance levels as follows:

The US Department of Defense military standard thus categorizes the 16 accident hazard indices (AHIs) into the following four safety assurance levels (SALs) for dealing with software safety risks: