When is an Assessment Body (AsBo) required?

An AsBo is required whenever a change to the railway system (technical, operational, or organizational) is classified as 'significant' according to the criteria defined in the CSM-RA regulation.

What is the difference between AsBo and ISA?

While both assess safety, an ISA typically focuses on technical compliance with CENELEC standards (like software safety in EN 50128) for specific products. An AsBo focuses on the broader risk management process of the entire system integration as required by EU law (CSM-RA).

Can the same company be both NoBo and AsBo?

Yes, many certification companies are accredited to act as both NoBo and AsBo. However, the personnel performing the assessments must maintain independence and objectivity for each specific role.

The Safety Validators: Understanding the Assessment Body (AsBo)

Safety requires verification. Understand how an Assessment Body (AsBo) evaluates risk management processes under CSM-RA to ensure safe railway integration.

December 11, 2025 8:26 am

What is an Assessment Body (AsBo)?

An Assessment Body (AsBo) is an independent organization responsible for assessing the safety and risk management processes of significant changes within the railway system. Their authority stems from the European Union’s CSM-RA (Common Safety Method for Risk Evaluation and Assessment) regulation.

Whenever a “significant” technical, operational, or organizational change occurs in the railway network (e.g., introducing a new signaling system or modifying operational rules), the proposer must appoint an AsBo. The AsBo’s role is to verify that the risk management process described in Regulation (EU) No 402/2013 has been correctly applied and that the system is safe for operation.

Core Responsibilities of an AsBo

CSM-RA Compliance Check: Verifying that hazard identification, risk estimation, and evaluation follow the legal framework.
Independence: Offering an unbiased third-party opinion, separate from the project design and implementation teams.
Safety Assessment Report (SAR): Producing the mandatory final report that concludes whether the system is safe to be integrated into the network.
Hazard Record Review: Auditing the Hazard Log to ensure all safety requirements are closed or transferred correctly.

Comparison: AsBo vs. NoBo vs. DeBo vs. ISA

Railway projects often require multiple types of assessors. Understanding the boundaries of each role is critical for successful authorization.

Role	Full Name	Focus Area	Governing Standard/Law
AsBo	Assessment Body	Safety & Risk Process	CSM-RA (EU Reg 402/2013)
NoBo	Notified Body	Interoperability (EU)	TSI (Technical Specifications for Interoperability)
DeBo	Designated Body	National Compatibility	NNTR (National Notified Technical Rules)
ISA	Independent Safety Assessor	Technical Safety (Product)	CENELEC Standards (EN 50126, 50128, 50129)

The CSM-RA Process Flow

The interaction with an AsBo typically follows these project phases:

1. System Definition & Significance Test

The project “Proposer” (e.g., Metro Operator) defines the system and determines if the change is “Significant.” If yes, an AsBo must be appointed immediately.

2. Hazard Identification

The AsBo reviews the project’s Hazard Analysis (HAZOP) to ensure all reasonably foreseeable hazards have been identified.

3. Risk Acceptance Principles

The project must demonstrate safety using one of three principles: Codes of Practice, Similar Reference Systems, or Explicit Risk Estimation. The AsBo validates the evidence for the chosen principle.

4. Final Safety Assessment Report (SAR)

Upon completion, the AsBo issues the SAR. This document is a critical part of the technical file submitted to the National Safety Authority (NSA) for the “Authorization for Placing in Service” (APIS).