SEA/Specific/TBT-SEA-015

Weather Monitoring and Stop Work Triggers

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Weather monitoring provides the data needed to decide whether construction activities can proceed safely.
Stop work triggers are pre-defined weather thresholds that require specific activities to cease immediately.
Common triggers include wind speed for crane operations, rainfall for earthworks, and temperature for concrete.
Wind speed limits for tower cranes are typically 38 mph; for MEWPs and mobile cranes, often 25–30 mph.
Lightning detection systems trigger evacuation of workers from exposed positions including roofs and scaffolds.
Rainfall intensity triggers halt earthworks compaction, concrete pours, and waterproofing operations.
Temperature triggers affect concrete placing (min 5°C), asphalt laying, and worker heat stress management.
Weather data can come from on-site stations, Met Office forecasts, or specialist construction weather services.
Trigger levels should be defined in the site safety plan and method statements for weather-sensitive activities.
The decision to stop or continue work rests with the site manager based on monitored data and trigger levels.

Prevent incidents	Weather-related incidents including crane collapse, scaffold failure, and lightning strike are preventable with triggers.
Quality protection	Work carried out in unsuitable weather produces defective results requiring costly rework.
Clear decision-making	Pre-defined triggers remove the pressure to continue working in dangerous conditions.

Don't

Define weather stop work triggers in the site safety plan for all sensitive activities
Monitor weather conditions using on-site instruments or specialist forecast services
Include wind, rain, temperature, and lightning triggers in crane and MEWP method statements
Brief site teams on the trigger levels at the start of each shift
Stop the relevant activity immediately when a trigger threshold is reached
Record weather monitoring data and all stop work decisions in the site diary
Evacuate workers from exposed positions when lightning is detected within range
Resume work only when conditions have improved and remain below the trigger level
Review trigger levels if site conditions or work methods change during the project
Use anemometers on cranes and at height to measure actual wind speed at work level

DON'T continue weather-sensitive activities when trigger thresholds have been reached
DON'T rely on ground-level conditions to judge wind speed at crane or scaffold height
DON'T override stop work triggers under programme pressure — safety takes priority
DON'T wait for conditions to worsen before acting — triggers exist to prevent incidents
DON'T ignore weather forecasts because current conditions look acceptable
DON'T leave trigger levels undefined — they must be in the plan before work starts
DON'T resume work immediately after a storm passes — confirm conditions are safe first
DON'T place concrete or lay asphalt below the specified minimum temperature
DON'T keep workers in exposed elevated positions when lightning is approaching
DON'T treat weather monitoring as someone else's responsibility — everyone should be aware

See also: Working in High Winds | Lightning Strike Procedures

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