Understanding CIMAH.
Managing major accident hazards.

What is CIMAH?

CIMAH stands for Control of Industrial Major Accident Hazards. Malaysia's CIMAH Regulations 1996 address major accidents involving hazardous substances, including serious releases, fires and explosions.

For a facility operator, the practical questions are straightforward: What could go wrong? Who could be affected? What controls are needed? How will the site respond?

FSC Engineering helps clients turn these questions into a clear technical assessment and practical safety documentation.

How do you know whether CIMAH applies?

The starting point is to identify the hazardous substances involved in your operations and the maximum quantities likely to be on site. This includes substances in the process and in storage. A check based only on today's stock may miss the larger quantity that could be present after a delivery or during normal operations.

These quantities are then compared with the relevant values in Schedule 2 of the CIMAH Regulations. This comparison helps establish whether the activity falls within the quantity exemption, the non-major hazard category or the major hazard category.

First, understand the threshold quantity (TQ)

A threshold quantity is the reference quantity listed for a particular hazardous substance or category. Different substances can have different threshold quantities, so there is no single tonnage that applies to every facility.

For a substance assessed individually, express the site quantity as a percentage of its TQ. Use the same units for both quantities:

For example, a result of 50% means that the site quantity is half of the substance's TQ. A result of 100% means that it has reached TQ. This percentage is an inventory comparison. It is not the probability of an accident or a measure of how safe the facility is.

Next, understand what the three classifications mean

The two reference points are 10% of TQ and 100% of TQ. They divide the initial quantity assessment into the following bands.

These bands explain the initial quantity assessment. A complete classification must consider all relevant substances and categories, the applicable quantity rules and any determination by the Director General under Regulation 7(2). See the regulatory references.

The worked example below shows how to apply this comparison to chlorine. It starts with chlorine's published TQ, identifies the two boundaries, and then shows how a change in storage quantity can change the classification.

Worked example: a facility handling chlorine

Assume that chlorine is the only relevant hazardous substance for this example. Schedule 2 lists its TQ as 10 tonnes, or 10,000 kg. The facility's maximum chlorine inventory is therefore compared with 10,000 kg.

The lower boundary is 10% of 10,000 kg, which is 1,000 kg (1 tonne). The upper boundary is the full TQ of 10,000 kg (10 tonnes). The bar below shows where the three bands sit between these boundaries.

Apply the calculation to the site inventory

Suppose the maximum inventory is eight containers, each holding 900 kg of chlorine. For this illustration, assume there is no additional chlorine elsewhere in the process or storage area. The total chlorine quantity is:

At 72% of TQ, the quantity is above the 10% exemption limit and below the 100% MHI boundary. It therefore falls within the NMHI band in this example.

Now suppose the facility increases its maximum inventory to twelve containers with the same chlorine contents:

At 108% of TQ, the inventory has crossed the MHI boundary. This illustrates why a proposed storage increase should trigger a review of the facility's CIMAH classification and the requirements that apply.

In both calculations, 900 kg is the weight of the chlorine contents, excluding the container itself. The container quantities are illustrative; an actual assessment must use the facility's inventory basis.

What happens after classification?

Classification establishes the applicable category. The technical assessment then examines the accidents that could occur, their possible effects and the measures needed to manage them. FSC structures this work around the facility and the reporting scope that applies.

1. Understand the facility

   We review the substances, inventories, process conditions, storage arrangements, site layout and nearby land uses. This establishes the basis for the assessment.

2. Identify credible accidents

   We consider how a loss of containment could occur and develop relevant accident scenarios. Depending on the substance and operation, these may involve toxic releases, fires or explosions.

3. Model the consequences and assess risk

   Consequence modelling estimates the possible effects of an accident. Risk assessment also considers how likely the event is and who could be affected.

   Drawing on our extensive experience in consequence modelling across various industries, FSC Engineering uses in-house software to calculate risk. We can also carry out the assessment using commercially available software to suit the client's preferences or project requirements.

4. Review prevention and mitigation

   We review the measures intended to prevent an accident or reduce its effects. These can include detection, isolation, containment, operating procedures, inspection and maintenance.

5. Prepare clear documentation

   We bring the study basis, assumptions, findings and recommendations together in a report that the client can review and use. Submission support is agreed as part of the project scope.

Connect the assessment to emergency planning

The accident scenarios should help the site plan its response. For example, a chlorine release assessment can inform discussions about alarms, isolation, evacuation, sheltering and coordination with emergency services.

FSC can support the review of emergency arrangements alongside the technical assessment, so the findings lead to practical actions.

How FSC Engineering can help

FSC Engineering brings together an experienced team with extensive process safety experience across different industries. We carry out explosion, fire and toxic dispersion modelling to help clients understand how an accident could affect their facility, their people and the surrounding area.

Our capabilities cover 2D consequence and risk assessments using Phast and Safeti, as well as computational fluid dynamics (CFD) modelling using FLACS. This allows us to select an approach that suits the questions your study needs to answer, from assessing potential impact distances and risk to examining how the facility's three-dimensional layout may influence dispersion and explosion effects.

Alongside these commercial tools, we have developed in-house software to suit specific client needs and have used it in previous studies. These tools support tailored calculations and assessments where a project requires a more specific approach. We can also use commercially available software where this is the client's preference or a project requirement.

We bring this modelling capability into our CIMAH assessments, connecting the technical findings with the site's safeguards, emergency arrangements and reporting needs. Our focus is on helping clients understand the findings and decide what actions are needed.

Whether you are planning a new facility, changing your hazardous substance inventory or reviewing an existing study, speak to FSC Engineering about the assessment your project needs.