Temporary structure, marquee and staging companies: the wind call, at your height

As an Operations or Site Manager, you are the competent person on site. You make the calls about when to build, when to derig, and when to take action on a temporary structure. These decisions are made per build and per event day, often under pressure.

A wrong call can lead to significant issues. If you misjudge conditions, you might face overtime costs for derigging, or the expense of replacing damaged structures. More critically, there are implications for personnel if a structure is compromised by wind.

Your decisions are guided by the maximum wind load ratings of each structure. You need clear information to plan your build and derig windows, and to know precisely when to strike a roof or lower trusses to prevent damage or collapse.

Your role involves protecting your crew, your equipment, and your client's event. Having clear, timely wind data helps you make these critical decisions with confidence, ensuring operations run smoothly and without incident.

For temporary structures, the crucial wind measurement is the gust at roof and truss height. This is typically around 15 metres above ground, but it depends on your specific structure's height. Wind speeds can vary significantly with height, so knowing the wind at your working level is essential.

The instrument interpolates wind speeds to your exact working height, showing you the gust beside the mean wind speed. This allows you to focus on the most impactful measurement for your structures.

Your limit is set by the supplier's wind calculation competent person, based on each structure's design. This is not a general guideline but a specific threshold for your equipment. You will enter this limit into the instrument, which then uses it to provide relevant alerts.

Understanding the difference between mean wind and gust is vital. Gusts are short, sharp increases in wind speed that exert sudden, powerful forces on structures, often exceeding the mean wind speed by a considerable margin. It is these gusts that typically dictate when you need to take action.

The instrument shows you the probability (P) that the wind will be above your set limit for each hour. This is calculated from an ensemble of weather models. If, for example, 20 per cent of these models predict wind above your limit, it indicates a low but present risk. At this level, you might proceed with caution, perhaps allocating extra crew for monitoring.

If the P(above your limit) rises to 50 per cent, it suggests a significant chance of exceeding your operational threshold. At this point, you might consider delaying non-essential work, preparing equipment for securing, or initiating preliminary steps to strike roofs or lower trusses.

When 80 per cent or more of the ensemble members show wind above your limit, the risk is high. This would typically trigger immediate action, such as halting all work at height, securing structures, or initiating full roof strikes or truss lowering procedures. The Agreement Spine shows you where the models agree or disagree, providing further context for these probabilities.

These percentages are not absolute commands, but a clear indication of risk, allowing you to align your operational decisions with your company's own action triggers, such as those in the Purple Guide.

Here is an example of how you might use the instrument during an event build:

• 06:00: Check the instrument for the 15-metre gust forecast. The P(above your limit) is 10% for the morning, rising to 30% by 14:00. You decide to proceed with the main structure build.
• 10:00: An alert arrives: P(above your limit) has risen to 45% for 16:00, with gusts of 40 mph forecast at 15m. You instruct the crew to prepare for potential roof striking later in the day.
• 13:00: A second alert shows P(above your limit) is now 65% for 17:00, with gusts of 45 mph. You decide to begin striking the roof of the main marquee, ahead of the forecast.
• 16:00: The wind increases as forecast, with gusts reaching 42 mph. The roof is already down, and the structure is secure. You notify the client of the proactive measures taken.
• 20:00: The wind has eased. You review the recorded forecast versus actual observations, noting your decision to act early prevented potential issues. The record is ready for sign-off.

Your operational limit for wind is a critical piece of information. It comes directly from your own documentation, typically derived from the manufacturer's specifications for each temporary structure. This might be expressed as a maximum wind speed, or more commonly, as action triggers at percentages of the structure's maximum wind load.

For example, industry guidance, such as the Purple Guide, often recommends taking action at 60% and 80% of a structure's maximum wind load. You will input these specific limits into the instrument. The instrument's preset height for this work is 15 metres, focusing on gust at roof and truss height.

Once entered, the instrument uses these values to calculate P(above your limit) and trigger alerts. This ensures that the wind information you receive is always directly relevant to your specific operational thresholds and the structures you are working with.

This precise setting means you are not relying on generic forecasts, but on data tailored to your operational needs, allowing you to make informed decisions based on your own established protocols.

For temporary structure operations, a clear and dated record of wind conditions and decisions is essential. The instrument provides a dedicated record page, documenting what was forecast, what was observed, the specific limit you used, and the call you made.

This record is invaluable for several reasons. Councils, particularly during event licensing, often require proof of due diligence regarding wind management. Having a single, dated page that shows what you knew and when, along with your actions, provides this necessary documentation.

Beyond regulatory requirements, this record serves as an internal audit trail. It helps you review past decisions, understand how forecasts aligned with actual conditions, and refine your operational procedures for future events. It also provides a factual basis if questions arise from clients or other stakeholders about your wind management decisions.

This archived information removes ambiguity and provides a transparent account of your decision-making process, protecting both your company and your crew.

Working with temporary structures in Ireland means contending with specific wind conditions, particularly due to the country's Atlantic exposure. The storm season typically runs from October to March, bringing higher wind risks, but significant wind events can occur at any time, impacting the main event season from April to October and Christmas markets.

Irish councils often apply guidance from documents such as the Purple Guide or IStructE recommendations as best practice during event licensing. This means your wind management plans need to align with these recognised standards.

The national forecaster, Met Éireann, provides general weather information, but for the precise, height-specific gust data needed for temporary structures, a more tailored approach is required. The instrument helps you meet these specific needs.

Understanding and preparing for these conditions is key to successful and incident-free operations. By focusing on gust forecasts at your specific working height and integrating your own structure limits, you can manage the challenges posed by Ireland's variable weather.