HSE wind limits, lightning rules, heat and cold stress thresholds — what outdoor workers need to know about working safely in all UK weather conditions.
Check today's site weather →This table provides general guidance based on HSE publications and industry standards. Always refer to your site-specific method statements, risk assessments and manufacturer guidance for specific equipment.
| Condition | Restriction | Action required |
|---|---|---|
| Wind above 38 mph (sustained) | Stop crane ops | Cease all crane lifting. Lower loads. Lash or secure loose materials. Scaffold inspection required after wind event. |
| Wind above 23–28 mph | Scaffold caution | Check manufacturer limits. Scaffold erection/dismantling should stop. WAH risk assessment triggered. |
| Lightning / thunder within 10 km | Stop all WAH | Immediately descend from all elevated positions. Seek shelter in solid building or enclosed vehicle. Wait 30 minutes after last thunder. |
| Temperature below 5°C | No concrete / mortar | Suspend concrete pours and masonry without heated protection. Frost blankets required for fresh concrete if overnight temp expected below 2°C. |
| Temperature above 27°C | Heat stress risk | Mandatory water provision. Rest breaks in shade. Monitor workers for heat exhaustion symptoms. Adjust work patterns. |
| Heavy rain (10mm+/hr) | Ground / electrical | Assess waterlogged excavations (collapse risk). Check electrical tool safety — GFCI protection required. Scaffold boards may become slippery. |
| Temperature below 10°C | Cold stress risk | Warm rest areas required. PPE includes insulating layers. Watch for signs of cold stress in workers. Hand warmers for fine-motor tasks. |
Lightning is one of the most acute weather hazards for site workers, particularly those working at height or in contact with metal structures, reinforcing steel or electrical equipment.
The industry-standard guidance is the 30-30 rule: if the time between a lightning flash and the corresponding thunder is 30 seconds or less, the storm is within 10km and all elevated work should stop immediately. Workers on scaffolding, roofs, lifting platforms or cranes must descend. Do not wait to see if the storm is moving closer — by the time you can make that judgment, it may already be too dangerous to descend safely. Wait 30 minutes after the last thunder before resuming work.
Construction sites often feature the highest structures in the local area — tower cranes, scaffold, and steel frameworks create elevated conductive pathways that attract lightning. Workers in contact with reinforcing steel (rebar) or metal formwork face additional risk even at ground level, as current can travel through a steel framework from a distant strike. Step potential — where current travels outward through the ground from a strike point — can also be lethal within 10–15 metres of a ground strike. Rubber-soled boots provide minimal protection against step potential.
Site electrical equipment — power tools, site lighting, temporary distribution boards — must be suitable for outdoor use (minimum IP44 rating for rain-exposed equipment). All temporary electrical installations must be GFCI (residual current device) protected. In heavy rain, inspect cable routes for waterlogged areas where cables may be submerged or in contact with water. Extension cables lying in puddles should be raised or removed from service. Switch off and isolate any electrical equipment that has been submerged in water and have it inspected by a competent person before re-use.
Heat stress is a significant and legally recognised risk for outdoor workers in the UK during warmer months. Workers in physical roles — particularly those in heavy PPE, working in direct sun on reflective surfaces — are at significantly greater risk than office workers.
The HSE considers heat stress a serious risk when: air temperature exceeds 27°C in direct sunlight; workers are in full PPE (high-vis vests, hard hats and steel-toe boots significantly reduce body cooling); work involves sustained heavy physical effort; and there is limited or no access to shade or rest areas. The wet bulb globe temperature (WBGT) is the most accurate measure of heat stress risk for workers — it accounts for humidity and radiation as well as air temperature, both of which matter significantly for workers in exposed locations.
Early signs include: heavy sweating; pale, clammy skin; rapid but weak pulse; nausea or dizziness; headache; weakness or fatigue beyond normal effort level. A worker showing these signs should stop work immediately, be moved to shade or a cool area, be given cool water to drink, and have clothing loosened. If symptoms do not improve within 15 minutes, or if the worker loses consciousness, this is a medical emergency — call 999. Heat stroke (hot, dry skin; confusion; loss of consciousness) requires immediate emergency response.
Employers are legally required under the Management of Health and Safety at Work Regulations 1999 to assess and control heat stress risk. Practical controls include: providing cold drinking water freely available — at minimum 250ml per hour per worker in hot conditions; scheduling the most physically demanding tasks for early morning (before 10am) or late afternoon (after 4pm); providing shaded rest areas; and modifying PPE requirements where risk permits — for example, using lighter-coloured high-vis instead of dark PPE in hot conditions.
UK winters regularly produce conditions that create cold stress risk for outdoor workers. Unlike heat, cold stress builds gradually and workers may not recognise when they are at risk.
Cold stress risk increases significantly below 10°C, particularly in wind (wind chill drops feels-like temperature substantially). Below 5°C, mandatory warm rest areas and appropriate insulating PPE are required. Workers' hands are particularly vulnerable — below 5°C, manual dexterity and grip strength decrease, which increases the risk of dropped tools and handling injuries. Fine-motor work (electrical connections, pipework fittings, small fasteners) should be avoided without insulated gloves that maintain dexterity.
Fresh concrete loses a significant proportion of its design strength if it freezes before achieving initial set (typically the first 24–48 hours). The hydration reaction that gives concrete its strength requires liquid water — when it freezes, the reaction stops and the ice expansion can damage the developing microstructure permanently. Under BS EN 13670 and the National Structural Concrete Specification, fresh concrete must be protected from freezing: use frost blankets on flat pours; use timber shuttering or insulated formwork for vertical pours; consider concrete admixtures with frost resistance for pours at temperatures approaching 5°C. Never pour concrete when temperatures are forecast to fall below 2°C overnight without a written cold-weather plan.
Wind speed at height is often significantly greater than at ground level — particularly on exposed sites without surrounding buildings to break the wind. A site in an urban location may have wind readings at ground level that underestimate conditions on the fifth floor by 40–60%.
The Lifting Operations and Lifting Equipment Regulations 1998 (LOLER) require that crane lifts are only carried out in conditions the equipment is rated for. Most tower cranes have a maximum operating wind speed of 38–45 mph (Beaufort Force 8), but specific manufacturers publish individual limits for each crane model. At sustained winds of 38 mph and gusty conditions above that, all crane lifts should cease. The crane operator has the authority and responsibility to stop lifts in unsafe conditions — this cannot be overridden by a project manager seeking to maintain programme.
Scaffold must be inspected by a competent person after any event where sustained winds exceeded 38 mph (Beaufort Force 8). Under NASC (National Access and Scaffolding Confederation) guidance TG20, the maximum design wind speed for standard scaffold is based on site exposure category — exposed coastal and hill sites have lower working limits than sheltered urban sites. Scaffold nets and sheeting dramatically increase wind load on a scaffold structure — these should be removed or rolled up when wind warnings are issued. Loose scaffold boards, materials and tools must be secured or removed from working platforms when high winds are forecast.
Heavy rain affects site safety in several distinct ways — from ground stability and excavation safety to electrical hazards and slippery surfaces.
Water-saturated ground adjacent to open excavations loses shear strength rapidly. This is the mechanism behind most excavation collapse incidents during or after heavy rain. The risk is highest in clay soils (which become plastic and mobile when saturated) and near water features. Ground support (trench boxes, shoring, battering) that may have been adequate in dry conditions requires reassessment after heavy rain. Under CDM 2015, geotechnical risks including water ingress must be managed and documented.
Scaffold boards, aluminium tower decks and metal access ladders become extremely slippery when wet or iced. Anti-slip board covers and tread plates should be used where boards are regularly walked on in wet conditions. Workers should be briefed to take extra care during and immediately after rainfall and to report any slippery access routes to their supervisor. Three-point contact on ladders is always required — in wet conditions, this should be enforced more strictly and checked by supervisors.
Get an instant weather verdict for your site location — wind, temperature, rain and any severe warnings checked together.
Check today's site weather →