Safeguarding Workplaces with CHRA: A Method-Specific Insight

In this article:

1. Key takeaways

2. Introduction

3. For whom is CHRA relevant?

4. Chemical exposure and hazardous substances

5. Purpose of CHRA

6. General description of the CHRA method

7. Participation

8. The CHRA methodology

   1. Identify work activities

   2. Identify the chemicals

   3. Assess exposure

   4. Assess the risk

On paper, hazardous chemicals are often well controlled; in practice, the main challenge is how people use and handle them during real tasks. The NORSOK S-002:2025 Chemical Health Risk Assessment (CHRA) method makes that interaction visible, by testing specific tasks against realistic exposure scenarios. This insight explains the method from NORSOK S-002:2025 (hazard category 1–5, exposure category and risk matrix) and shows how to turn workshop findings into engineering and operational improvements.

Key takeaways

• CHRA is a workshop-based, task-based method: it assesses exposure to hazardous chemicals by reviewing specific work activities (operations, maintenance and non-routine work) and agreeing on realistic barriers/work conditions in a structured worksheet.

• Hazardous chemicals are categorised: assign health hazard category (1–5) using Safety Data Sheets and CLP hazard statements (H-phrases) to represent intrinsic severity.

• Exposure is scenario-specific: consider inhalation and skin exposure routes and set the exposure category (low/moderate/high) based on how the task is performed and barrier effectiveness—typically benchmarked against occupational exposure limit values.

• The matrix drives prioritisation: combining hazard and exposure in the CHRA risk matrix makes the basis for decisions transparent and indicates where risks can be reduced the most.

• Design actions come first: use the results to eliminate/substitute where possible and engineer out exposure (closed systems, ventilation, containment, access/maintainability) before relying on procedures and Personnel Protective Equipment (PPE).

Introduction

Across Europe, frameworks such as REACH and CLP require employers to understand and control chemical risks, not only by listing substances, but by ensuring that work is designed in a way that  people are not harmed. A CHRA supports this by connecting legal duties to day-to-day tasks, barriers and decisions.

In practice, CHRA is a structured, workshop-based review where a multidisciplinary team walks through operations and maintenance tasks, identifies where exposure to hazardous chemicals could occur (inhalation and/or skin contact), and agrees what barriers are relied upon. The outcome is a documented worksheet and a prioritised list of actions to reduce exposure to As Low As Reasonably Practicable (ALARP).

The goal is to design the work, workplaces and processes so that exposure to hazardous chemicals is avoided, or, where it cannot be eliminated, reduced to ALARP.

For whom is CHRA relevant?

The NORSOK S-002:2025 CHRA method is most commonly associated with offshore energy projects, but its real value is broader: it helps any organisation move from “we have hazardous chemicals” to “we understand which tasks create exposure and which barriers we are relying on”. The method transfers well to other sectors as long as you keep the same discipline: task-based scenarios, hazard categorisation (1–5) from SDS/CLP, exposure categorisation, and a transparent risk matrix to drive ALARP decisions. Other sectors may be:

• Manufacturing and processing plants

• Laboratories and hospitals

• Construction and surface treatment

• Food production and cleaning operations

• Battery, hydrogen, or energy facilities

• Waste handling and recycling

Different sectors have different chemical inventories, but the CHRA logic stays consistent: describe the task, challenge the assumed barriers, and use hazard category, exposure category and the matrix to prioritise what to change first. The next section summarises how chemical exposure typically occurs and why the same few exposure routes matter across most workplaces.

Chemical exposure and hazardous substances

In CHRA, “chemical exposure” is not an abstract number; it is what happens when a person is close enough to a source, for long enough, with weak enough barriers. Hazardous substances can enter the body mainly through inhalation and skin contact (and less commonly ingestion), and the practical question is: what form is the contaminant in, and how could it reach the worker during the task?

Airborne contaminants show up in different forms (see Figure 1), and that matters because control measures differ: gases and vapours tend to drive ventilation/containment decisions, while mists, fumes and dusts often require capture, enclosure, and maintenance-friendly cleaning/housekeeping.

Figure 1 The most common types of airborne contaminants.

Hazardous chemicals can cause immediate effects (e.g., irritation, burns, acute toxicity) or long-term harm (e.g., sensitisation, organ damage, cancer). In the NORSOK S-002:2025 CHRA method, this intrinsic harm is captured through health hazard categories, but exposure still depends on the task: whether the system is open or closed, how often the task occurs, and how reliable the barriers are.

Benzene is a useful illustration of why CHRA focuses on both hazard and exposure: it has a high intrinsic hazard (carcinogenic), and it may be present in routine process streams. When routine tasks involve breaking containment (sampling, draining, opening equipment), even “small” releases can drive meaningful exposure potential. Less dramatic substances, such as oil mist, may sit in lower hazard categories, yet still create chronic health risk when exposure is frequent or long-lasting. CHRA is designed to surface these “everyday” exposures that can be overlooked in other design reviews.

Importantly, chemical risk management covers both chemicals that are intentionally used (e.g., cleaning agents, paints, fuels) and substances generated by the work itself (e.g., welding fumes, diesel exhaust). CHRA treats both in the same way: describe the task and barriers, then assess exposure potential against relevant limits.

Purpose of CHRA

The purpose of CHRA is to provide a repeatable, transparent basis for deciding whether exposure to hazardous chemicals is acceptable, or, if not, what must change. Practically, CHRA is used to (1) identify which work tasks require exposure barriers, (2) prioritise risk-reduction measures to achieve ALARP (design first, then operational controls/PPE), and (3) confirm that emergency showers and eyewash stations are located and specified so they are available for the scenarios identified.

General description of the CHRA method

In NORSOK S-002:2025 Working Environment, CHRA is the required way to identify, evaluate and demonstrate, within project governance, that health risks from hazardous chemicals are controlled. In practice, that means starting chemical mapping as early as possible (known equipment, tasks and associated chemicals), typically through WEHRA and package follow-up in the feasibility and concept phases and then performing a more detailed CHRA in FEED and the execution phase. The scope should be proportionate to the project’s nature, chemical inventory and exposure risk.

The workshop itself can be divided into four parts where the following main steps are included:

1. Identify work activities

2. Identify chemicals

3. Assess exposure

4. Assess the risk

   
   

Normally, the CHRA worksheet, exemplified in Table 5, is prepared as far as possible before the workshop by implementing step 1 and 2. Input to the workshop is usually based on, but not limited to, the following:

• Working Environment Health Risk Assessment (WEHRA)

• Dispersion analysis

• Plot plans

• Vendor package information

• Escape routes and safety equipment plans

• Safety Data Sheets

• Measurements from similar work situations can be used as part of the documentation

Participation

CHRA works best as a multidisciplinary discussion. The workshop should include the risk owner (project management and/or the operating company), relevant engineering and technical disciplines, a chemical working environment specialist, end users/operations, and an employee representative (e.g., safety delegate).

The CHRA methodology

CHRA approaches can vary slightly between organisations, for example in worksheet structure and the way the risk matrix is presented. This article follows NORSOK S-002:2025 and uses the health hazard categories, exposure categories and chemical risk matrix defined in that standard.

1.      Identify work activities

Start by identifying the activities and equipment where people could be exposed to hazardous chemicals through inhalation and/or skin contact. In the NORSOK S-002:2025 method, particular attention is given to chemical groups in health hazard category 3 or higher, as these often drive the need for stronger engineered and operational barriers. It is important to capture the full lifecycle of interaction, handling, transport, storage, use, maintenance and disposal, and list each activity together with the associated chemical/chemical group in the CHRA worksheet (Table 5).

2.      Identify the chemicals

In CHRA, “identifying the chemical” is about identifying its intrinsic health hazard. That information is taken from the Safety Data Sheet (SDS), specifically the CLP classification and hazard statements (H-phrases) defined under the EU Classification, Labelling and Packaging (CLP) Regulation (EC) No 1272/2008.

NORSOK S-002:2025 groups chemicals into health hazard categories to make the next steps in the worksheet consistent. The scale runs from 1 (insignificant) to 5 (very serious) and reflects severity by nature, before you consider how the chemical is handled in a specific task.

For example, benzene in process streams carries the hazard statement H350 (“May cause cancer”) and is therefore placed in health hazard category 5 (very serious) in the NORSOK S-002:2025 CHRA method. Table 1 shows the relevant category and other examples from the standard.

Table 1 Health hazard categories – a selection of examples (Source: NORSOK S-002:2025 Working Environment)

Table 2 shows examples of selected chemicals and their typical health hazards.

Table 2  Examples of chemicals in use offshore (Source: NORSOK S-002:2025 Working Environment).

3.      Assess exposure

Assess exposure by comparing the expected exposure potential with relevant Occupational Exposure Limit Values (OELVs). If exposure cannot reasonably be ruled out, for example, where screening indicates it could exceed 10% of the applicable limit, a CHRA exposure assessment should be completed for the task.

The exposure category describes how much people may be exposed during a specific task, given the way the chemical is handled and how effective the barriers are (e.g., closed systems, ventilation, segregation, procedures). It is not a property of the chemical itself; it is a description of the exposure scenario under defined operating conditions.

In the NORSOK S-002:2025 CHRA method, the exposure category is combined with the health hazard category (intrinsic hazard) to determine the resulting health risk in the matrix. The exposure category is typically set by considering the influential factors shown in Figure 2.

Figure 2 Determination of exposure category by including influential factors.

Exposure category levels which are typically used in CHRA are shown in Table 3. Exposure is commonly classified into three qualitative levels, based on comparison with applicable exposure limits: High-, moderate- and low.

Table 3 Exposure category levels (Source: NORSOK S-002:2025 Working Environment).

These categories provide a structured way to express how much exposure is expected, rather than relying on absolute concentration values alone.

4.      Assess the risk

In CHRA, health hazard category describes the chemical’s intrinsic severity (how harmful it is by nature), while exposure category describes the task scenario (how much people may be exposed, given the way the work is performed and the barriers in place). The CHRA risk matrix combines these two perspectives to determine whether the resulting health risk is low, moderate or high, and therefore how urgent and how far risk reduction must go to achieve ALARP.

Returning to the benzene example: benzene is classified as carcinogenic (H350 “May cause cancer”), which places it in health hazard category 5 (very serious) in the worksheet example (Table 5). If the relevant task involves handling or maintenance in an open system with frequent manual interaction (e.g., pig receiver activities), the exposure category is likely moderate to high. When these categories are combined in the CHRA risk matrix (Table 4), the resulting risk is high, indicating that risk-reducing measures are required.

Table 4 Matrix for chemical risk assessment (Source: NORSOK S-002:2025 Working Environment).

Finally, a CHRA only creates value if the outcomes are documented, owned and closed out. High risks require prioritised risk-reduction actions; moderate risks may be considered controlled but should still be challenged against ALARP; and low risks are generally acceptable with no further action. Where possible, risk reduction should be driven through design changes (elimination/substitution and engineering controls) before relying on procedures and PPE. The workshop results, assumptions, decisions and actions, are typically captured in the CHRA worksheet and summarised in a CHRA report.

Table 5 Example of a simplified CHRA Worksheet.