An Activity-Based Costing Framework for Occupational Safety and Health Management Costs in Modular Building Installation

In the world of construction, safety is not just a matter of wearing a hard hat; it is a massive, complex system of planning, equipment, and human coordination that costs money. In South Korea, the law requires construction companies to set aside a specific budget for safety, but this money is tracked using a simple list of categories, like "training" or "protective gear." This method works well for checking if a company has spent the right amount of money on the right types of items, but it struggles to explain how that money is actually used during the specific, high-stakes moments of a job. Imagine trying to understand how a car engine works by only looking at the total amount of fuel in the tank, without knowing which part of the engine burned that fuel or why the consumption changed when the car went up a hill. This gap between the total budget and the actual work being done is the problem researchers are trying to solve, especially for a modern building technique called modular construction.

Modular construction is like assembling a giant set of prefabricated rooms. Instead of building a wall brick by brick on the site, large three-dimensional units are built in a factory and then trucked to the location. Once they arrive, a massive crane must lift them into place, land them, align them perfectly, and bolt them together. This process happens in rapid, repeated cycles. The danger is that all the risks—falling loads, unstable platforms, and communication breakdowns—happen in a very short window of time. Because the work is so fast and repetitive, the safety costs do not stay the same; they change depending on how many units are being lifted, how long the crane is working, how many connections need to be made, and how many shifts the crew works. The current system, which just looks at the total bill, cannot see these changes. It cannot tell a manager if a cost went up because the job got bigger, or because the wind made the lifts take longer.

To fix this, a researcher at Gyeongsang National University developed a new way of looking at these safety costs, called an activity-based framework. Instead of just counting the total money spent on safety, this new system breaks the job down into the actual steps where safety matters most. The researcher identified five main stages of the modular installation process: the arrival of the modules, the preparation for lifting, the actual lifting, the landing and alignment, and the final connection. For each of these stages, the system identifies specific safety tasks, such as setting up barriers, checking the wind, or holding a safety briefing. It then links the money spent to these specific tasks and the people responsible for them.

The researcher tested this new system using a simulated project where the total eligible safety cost was normalized to 100 units, representing a case with 20 modules and 12 lift-hours. The goal was not to find out exactly how much a real building costs, but to see if the new math worked correctly. The test showed that the system was perfectly balanced. Every dollar of the original safety budget was accounted for, moving from the general categories into the specific tasks, and finally into the five stages of the job. Nothing was lost, and nothing was invented. The system successfully showed that if you increase the number of modules to be lifted, the cost for lifting-related safety tasks goes up, but the cost for tasks unrelated to lifting stays exactly the same. This is a crucial difference from the old way of doing things, where a change in one part of the job might accidentally change the budget for everything else.

The study also proved that this new method makes it much clearer who is responsible for what. In the old system, it was often hard to tell who needed to prepare a specific safety measure before the work began. In the new system, every safety task has a named owner, a specific time by which they must be ready, and a list of proof that they are ready. For example, before a crane lifts a module, the system requires proof that the lifting plan was approved, the route was checked, and the wind was monitored. If any of these pieces of evidence are missing, the system flags it as a problem before the dangerous work starts. This shifts the focus from simply paying bills to ensuring that the safety controls are actually in place when the workers need them.

The results of this simulation suggest that construction managers could use this framework to plan their safety budgets more intelligently. Instead of guessing how much money they need for a new project, they could look at the specific drivers of their work, like the number of lifts or the number of connections, and calculate the exact safety resources required. The system allows them to see that adding more modules will increase the cost of lifting safety, but adding more shifts will only increase the cost of shift-based briefings. This level of detail helps managers understand exactly why their costs are changing and ensures that they are not overspending on things they do not need or underspending on things that are critical.

However, the researcher is careful to note that this is a model, not a final rulebook for the industry. The numbers used in the test were hypothetical, designed to show that the logic works, not to represent the actual prices of safety gear or labor in South Korea. The study proves that the framework is mathematically sound and logically consistent, but it does not yet prove that it will save money or prevent accidents in the real world. To do that, the system would need to be tested with real data from actual construction sites. The researcher concludes that while the current law requires a specific list of safety expenses, this new framework offers a way to understand the story behind those expenses, linking every dollar to a specific action, a specific person, and a specific moment in time. It turns a static list of costs into a dynamic map of safety, helping to ensure that the right resources are ready exactly when the danger is highest.