Task: Update Dependability Analysis

The dependability analysis - including the hazard analysis (safety), reliability analysis, and threat analysis (security) should be frequently reviewed and updated as design decisions are made, solutions are modified, and requirements change.

Purpose

The purpose of this task is to ensure that the dependeabilty analyses of the system remains valid throughout the life of the project.

Relationships

Roles	Primary: Safety Czar	Additional: Reliability Czar	Assisting:
Inputs	Mandatory: Hazard Analysis	Optional: Failure Modes and Effect Analysis Fault-Tree Analysis Threat Analysis	External: None
Outputs	Failure Modes and Effect Analysis Fault-Tree Analysis Hazard Analysis Threat Analysis

Main Description

The hazard analysis is a key document for safety critical systems as it combines the description of the hazards, the level of risk, system faults that can lead to the hazard, and the control measures all together in a single view. The Fault is a non-compliance of the system that can lead to the identified hazard. The severity is a measure of how bad the hazard is (an arbitrary scale of 1-10 is used often used). The Risk is a value computed by the likelihood multiplied by the severity of the occurrence. This task keeps the hazard analysis up to date, re-performing fault tree and failure modes and effect analyses as appropriate.

Reliability analyses are often maintained in Fault Means Effect Analyses. As technology decisions are made, this can impact the reliabilty of the system and availability of services. These analyses must reflect actual reliability numbers are development progresses.

Security analyses are represented in many ways, but a threat assessment or threat analysis document or model is most common. These analyzes identify the assets requiring protection, their vulnerabilities, and the countermeasures put into place to protect them. These analyses must also be kept up to date.

Steps

Examine changed elements for dependability impact

As requirements change or design decisions are made, these can increase or decrease safety, eliability or security (or all three). Those changes must be examined to see if they impact or even invalidate the existing hazard, reliabilty, and/or threat analysis.

Perform Fault Tree Analysis

FTA analyses how faults and conditions interact to produce hazards.

Perform Failure Modes and Effect Analysis

FMEA looks at how failures accumulate to produce undesirable conditions (hazards).

Perform Threat Analysis

Threat analysis examines the important assets of the system, the vulnerabilities they exhibit, and the countermeasures put into place to protect them.

Identify new and changed dependabilty concerns

As designs progress, design decisions are made that can positively or negative affect the dependability of the system by adding or changing dependability concerns.

Quantify risks for new or changed dependability concerns

Risks need to be determined by quantifying the nature of the dependabilty concerns in terms of likelihood and severity.

Update Dependability Analyses

The depoendability analyses must need be updated when a change in requirements, design, or environment affects the dependability of the system.

More Information

Guidelines	Fault Tree Analysis Hazard Analysis Guideline