At about 17.09 local time on 4 March 2026, heavy rain and strong wind toppled a piece of heavy equipment on the Kaligawe segment of the Semarang-Demak toll road project. The project's commitment officer said no one was killed or injured (kumparanNEWS, 2026). Three weeks later, Indonesia's weather agency BMKG warned of whirlwinds during the transition season, events that are short-lived but can still damage buildings and bring down trees (Galuh, 2026).
April is a transition month in much of Indonesia, and the weather on a project site can turn within minutes. An interim report for the Florida Building Commission notes that incidents caused by high winds account for almost a quarter of crane accidents (Bridge, 2026). The practical question is which wind figure should decide whether a lift may start or must stop.
How We Compare
We compare three common approaches against four criteria: what is measured, at what height, what data are needed, and whether the shape of the load is taken into account. In Indonesia, Minister of Manpower Regulation No. 8 of 2020 requires employers to apply occupational safety and health requirements to lifting and conveying equipment (Kementerian Ketenagakerjaan, 2020), while the operational wind limit itself comes, in practice, from the manufacturer's manual and load chart (European Materials Handling Federation [FEM], 2017).
The Weather Forecast
BMKG forecasts and warnings help plan lifting days, postpone major lifts and put cranes in a safe configuration before the weather turns. The weakness lies in how the number is defined. Weather stations usually report a 10-minute average at 10 metres above ground, whereas the figure in a crane load chart under EN 13000 is a 3-second gust at the highest point of the boom system, and that gust can be twice the average or more (FEM, 2017).
FEM (2017) gives an example. A weather station reports 6.2 m/s at 10 metres. At a lifting height of 50 metres, the expected 3-second gust reaches 13 m/s, above the 9 m/s allowed in the load chart, so the lift must not go ahead. A forecast that sounds moderate turns out to exceed the machine's limit.
The Load Chart Limit
The second approach uses the wind limit in the load chart, read from an anemometer at the boom tip. EN 13000 requires a wind speed indicator on mobile cranes with a jib combination longer than 65 metres or a stowing time of more than 5 minutes, and FEM recommends visual and functional checks of the anemometer at least once a year (FEM, 2017).
Its strength is that the reading is the same kind of number as the chart. Its weakness is that the chart assumes a load with a projected area of 1 square metre per tonne and a drag coefficient of 1.2, or a wind area of 1.2 square metres per tonne. Wind from the side is also not detected by the crane's rated capacity limiter, so the crane can be overloaded without any warning (FEM, 2017).
Calculating Each Load
The third approach calculates the permissible wind speed for a specific load: the chart limit multiplied by the square root of 1.2 times the load mass divided by projected area times drag coefficient, capped at the chart limit. In the FEM (2017) example, a 50-tonne load with a projected area of 77 square metres and a drag coefficient of 1.3 has a wind area of about 100 square metres, or 2 square metres per tonne, so the 9 m/s chart limit drops to 7 m/s. That 7 m/s is not programmed into the crane's computer, so the operator must watch for it.
This approach is the most precise but needs the mass, dimensions and shape of the load and a planner who understands them. In our view it is also the step most often skipped on building and road projects, even though precast wall panels, roof trusses and formwork all have a large wind area relative to their mass.
Which One to Use
The three work together. Forecasts serve planning and scheduling, the chart limit read from an anemometer serves the start and stop decision on site, and per-load calculation is essential for loads with large surfaces. Stop thresholds belong in the lift plan and the permit to work, together with who has the authority to halt a lift. The Florida report adds that idle cranes also need preparing for high winds, for example by lowering booms and letting tower crane jibs weathervane freely as the manufacturer recommends (Bridge, 2026).
The evidence has limits. The FEM calculations were written for mobile cranes in Europe's wind turbine sector, and the quarter-of-accidents figure comes from a US literature review. Data on wind-related crane accidents in Indonesia are not publicly available.
How Nusa Safety Helps
Nusa Safety helps project teams write lift plans and stop thresholds through its risk assessment and JSA workshop, prepares operators and riggers through lifting operator and rigger training delivered with licensed PJK3 partners, and assesses equipment condition through a machine safety assessment.
This article is general information, not legal or professional advice for any specific case.
References
- Bridge, J. A. (2026). Best practices for hurricane season utilization of tower cranes and hoisting equipment (Interim report). Florida Building Commission and University of Florida. https://www.floridabuilding.org/fbc/commission/FBC_0426/HRAC/Crane_Interim_Report.pdf
- European Materials Handling Federation. (2017). FEM 5.016: Safety issues in wind turbine installation and transportation (3rd ed.). https://www.fem-eur.com/wp-content/uploads/2016/02/CLE-5016-EN-2017.pdf
- Galuh, M. (2026, March 23). Waspada puting beliung saat pancaroba, kenali tanda dan cara menghadapinya [Beware of whirlwinds in the transition season: signs and responses]. Kompas TV. https://www.kompas.tv/info-publik/658640/waspada-puting-beliung-saat-pancaroba-kenali-tanda-dan-cara-menghadapinya
- Kementerian Ketenagakerjaan. (2020). Peraturan Menteri Ketenagakerjaan Nomor 8 Tahun 2020 tentang Keselamatan dan Kesehatan Kerja Pesawat Angkat dan Pesawat Angkut [Minister of Manpower Regulation No. 8 of 2020 on occupational safety and health of lifting and conveying equipment]. https://peraturan.bpk.go.id/Details/163270/permenaker-no-8-tahun-2020
- kumparanNEWS. (2026, March 4). Diterjang angin kencang, alat berat proyek Tol Semarang-Demak roboh [Heavy equipment on the Semarang-Demak toll project collapses in strong wind]. kumparan. https://kumparan.com/kumparannews/diterjang-angin-kencang-alat-berat-proyek-tol-semarang-demak-roboh-26x5qmGFsGa
