Wind limit for a tent, hoist and drone

First: mean wind or gust?

The wind figure in a weather forecast is usually a 10-minute mean wind. A gust is a momentary wind lasting a few seconds, and according to the Finnish Meteorological Institute gusts are typically about 1,5 times and at most about twice the mean wind. If the forecast promises a mean wind of 8 m/s, gusts can therefore be about 12–16 m/s.

Tents, lifts and drones topple or fly away in a momentary gust, not in the average wind. That is why you should always compare the equipment's wind limit with the forecast gusts. Wind warnings for land areas are based precisely on gusts, whereas warnings for sea areas are based on average wind.

Pop-up tent and event tent

The rescue sector's guidance contains minimum weights for tarpaulin-roofed tents when loose weights are used. The weights are dimensioned for wind of up to 15 m/s. In a storm or in wind above 15 m/s, tents must be secured more effectively or their use stopped, and people are moved away from the vicinity of the tents.

A tent is secured according to the manufacturer's or a qualified designer's instructions. For tents up to 300 m², securing is done with ground anchors or weights with lines whose tensile strength is at least 1,000 kg; ordinary string is not acceptable.

According to Tukes, counterweights alone do not necessarily prevent a lightweight tent from sliding sideways, so sideways movement is prevented with stakes or additional weights. In tents over 300 m², illuminated exit signs that run on backup power are also required.

2 × 2 m tent: at least 15 kg on each leg
4 × 4 m tent: at least 62 kg per leg
5 × 5 m tent: at least 96 kg per leg
6 × 6 m tent: at least 139 kg per leg

Aerial work platform

The wind limit of an aerial work platform is found in the marking attached to the machine. According to the International Powered Access Federation IPAF, the maximum design wind speed of a platform intended for outdoor use under standard EN 280 is 12.5 m/s. Machines intended only for indoor use have no wind limit suitable for outdoor work.

IPAF reminds that wind strengthens with height and at a height of 20 metres can be about 50 % stronger than at ground level. Boards and signs carried in the basket act as a sail, and tall buildings can channel the wind locally. Wind can be measured at working height with an anemometer.

Drone

There is no single m/s limit written into law for flying a drone. According to Traficom, the manufacturer states the maximum recommended wind for commercial drones, and the remote pilot must find out and observe it. A drone carrying a payload may not cope even in the wind the manufacturer states.

According to Traficom, wind generally strengthens at altitude, and behind buildings, forest edges and other obstacles there is strong turbulence. In the open category, flights are made at a maximum height of 120 metres and within visual line of sight, so the wind aloft can be considerably stronger than at the take-off site.

A wind warning is not the wind limit for the work

The Finnish Meteorological Institute's yellow wind warning is issued for land areas in the summer season at gusts of 15 m/s and in the winter season, starting 1.11., at gusts of 20 m/s. Many devices are dimensioned for lower wind: a typical limit for a mobile elevating work platform is 12,5 m/s, and tent weights are calculated for 15 m/s wind. Work or an event may therefore have to be interrupted even if no warning has been issued.

How to make the wind decision in advance

The clearest way is to decide the limits before the event or job and write them down. If at least 200 people are present at the same time at a public event, a rescue plan is required, which must be submitted to the rescue authority no later than 14 days before the event. Weather risks and wind limits should be handled in the same plan.

Record the manufacturer's wind limit for every tent, stage and machine.
Appoint a person who follows the forecast gusts and the local wind.
Decide in advance in what wind conditions the tent will be emptied or the lift interrupted.
Follow up-to-date wind warnings and the Beaufort scale in Wind Radar.

Frequently asked questions

In how strong a wind does a pop-up tent hold?

The minimum weights in the rescue sector's guidance are dimensioned for wind of up to 15 m/s. In stronger wind the tent must be secured more effectively or its use stopped. The manufacturer's instructions always take precedence.

What is the wind limit for a personnel lift?

The limit stated by the manufacturer on the machine is decisive. According to IPAF, the design wind speed of an outdoor lift complying with EN 280 is 12.5 m/s.

Is there a legal wind limit for flying a drone?

There is not. According to Traficom, the remote pilot must observe the maximum recommended wind stated by the manufacturer.

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Sources

The article is general information and does not replace the guidance of an authority, a lawyer or an adviser. Check up-to-date information from the sources.

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