Main contractors' site managers and construction managers (CIF members): the wind call, at your height

Every morning, you decide which trades can work at height and until what time. This includes crane operations, MEWPs, roof work, glazing, sheeting, and deliveries. You make this call daily, typically at 06:30, and again at lunchtime to adjust for changing conditions. This decision directly affects your daily programme.

A wrong call can have significant consequences. For example, during Storm Éowyn in January 2025, scaffolding collapse blocked a road in Dublin. The HSENI advised avoiding all work at height and suspending all lifting operations during that storm. Beyond maintaining project timelines, incorrect wind calls can lead to missed completion dates and liquidated damages, which are specific to your contract terms.

Your decision is critical for site operations and project timelines. You need clear information to make these calls consistently, ensuring that work proceeds when conditions allow and is halted when limits are exceeded. The instrument provides a clear view of wind conditions at your working height, helping you to make these daily assessments.

Wind conditions vary significantly with height. The instrument shows wind at 10, 80, 120, and 180 metres, then interpolates this data to your specific working height. This ensures you are looking at the wind relevant to your operations, not just ground-level readings.

For work at height, the critical measurement is often the gust at your working height, not the mean wind speed. Your own site rules and risk assessments (RAMS) will specify whether to use gust or mean wind for particular activities and machines. For example, a standard outdoor MEWP might have a limit of 12.5 m/s gust, while roof work might be 10.3 m/s, and mobile alloy access towers 7.6 m/s.

Your limit for a specific activity is set by the manufacturer's specifications, your site rules, or your risk assessment. You input this limit into the instrument, which then shows the wind conditions in relation to that threshold. Heights below 10 metres are extrapolated below the lowest model level and are badged as such, indicating that these are derived values.

The instrument provides the probability (P(above your limit)) by the hour, computed from ensemble members at 10, 80, 100, and 120 metres. This fraction of ensemble members indicates how many of the different model runs predict wind speeds above your set limit for that hour. It is not a calibrated certainty, but a measure of how widespread the prediction is among the models.

The Agreement Spine shows where the various weather models agree on wind conditions and where they do not. This helps you understand the confidence level in the forecast. If the models largely agree, the forecast is more reliable. If they disagree, there is more uncertainty, and you might need to be more cautious.

Here is how you might act on different probabilities for your work:

• 20 per cent: This low probability suggests that most models predict conditions below your limit. You would likely proceed with work, monitoring for any changes.
• 50 per cent: At this level, half the models predict exceeding your limit. You might plan to proceed but with a contingency, such as having alternative tasks ready or preparing to stand down specific trades.
• 80 per cent: A high probability indicates that most models predict conditions above your limit. You would typically re-plan work, postponing height-related tasks and informing affected trades the night before.

This is an example of how you might use the instrument during a typical workday:

• 06:30: You check the instrument. For your crane, set to 40 metres with a gust limit of 12.5 m/s, the P(above your limit) shows 10 per cent until 14:00, then 60 per cent from 14:00 to 17:00. The Agreement Spine shows good model agreement for the morning, but increasing divergence in the afternoon.
• 06:45: You brief the crane team, confirming they can operate until 14:00, but must be ready to stand down or switch to ground-level tasks after that. You also check the forecast for roofers (10.3 m/s limit) and MEWP operators (12.5 m/s limit), seeing similar afternoon probabilities.
• 12:30: You re-check the instrument. The 14:00 to 17:00 P(above your limit) for the crane has increased to 70 per cent, with stronger gusts now forecast. The Agreement Spine shows continued model divergence, but with a trend towards higher wind speeds.
• 12:45: You inform the crane team to complete their current lift and prepare to stand down by 13:30. You also notify the roofers and MEWP operators that their work at height will be suspended from 13:30. You assign alternative tasks for the afternoon.
• 17:00: You review the day's record on the instrument, noting the forecast, the observed wind, your set limits, and the decisions made. This record is stored for your project documentation.

Your working limit for wind speed is specific to each activity and piece of equipment on your site. This limit is not set by the instrument; it comes directly from your own operational documents, such as manufacturer's manuals, site-specific risk assessments, or method statements. For instance, a standard outdoor MEWP might have a manufacturer-set limit of 12.5 m/s gust, while roof work might be 10.3 m/s, and mobile alloy access towers 7.6 m/s, as per HSENI guidance.

When you use the instrument, you will input these limits directly. The instrument provides a preset for a crane at 40 metres with a gust limit of 28 mph (approximately 12.5 m/s), which you can adjust. This ensures that the instrument's display is always relevant to your specific operational thresholds.

By typing in your exact limits, you ensure that the wind data is presented in a way that directly supports your decisions. The instrument helps you monitor conditions against your specific thresholds, allowing you to make informed calls based on your own documented requirements.

The instrument maintains a dated record page of what was forecast, what was observed, the limit you used, and the call you made. This record is a critical component for your project documentation and for demonstrating due diligence.

For site managers, this record serves multiple purposes. It provides an auditable trail for internal reviews, external inspections, or in the event of an incident. If a question arises about a decision made on a particular day regarding work at height, this record provides objective data to support your actions. It shows that you consulted available information and made a considered decision based on the wind conditions and your operational limits.

This record is often requested by project auditors, clients, and regulatory bodies. It demonstrates a systematic approach to managing wind-related risks on site. Having a clear, unalterable log helps you account for your decisions and contributes to the overall project management system. The record page captures the wind data, your limit, and your decision, providing a comprehensive snapshot of each day's wind management.

Ireland's geographical position means it is frequently exposed to strong winds, particularly during the autumn and winter months. The storm season typically runs from October to March, bringing named storms that can significantly impact construction operations. For example, Storm Éowyn in January 2025 caused disruption and prompted specific advice from the HSENI regarding work at height.

These conditions make accurate wind forecasting and monitoring essential for construction sites across the island. The Atlantic exposure means that wind speeds can change rapidly, and gusts can be particularly challenging for work at height. Met Éireann provides national weather forecasts, but site-specific data at working height is crucial for daily operational decisions.

Understanding these seasonal patterns and the potential for sudden changes is key to effective site management. The instrument helps you anticipate and respond to these conditions, allowing you to re-plan work the night before a predicted storm or adjust schedules during the day as conditions evolve. This proactive approach helps to minimise disruption and maintain operational standards.