What hotter summers mean for the health of people on and around the railway

Higher average temperatures, more frequent heatwaves, and an increased number of sunny days in the UK will increase the risks of several short- and long-term health issues. Many of these risks can be reduced through simple awareness and minor behavioural changes, which can go a long way in protecting the health of people on the railway. 

Immediate health impacts

Several illnesses are directly caused by hot weather. For many heat-related conditions, the best treatment is typically to move the person to somewhere cooler and to cool them down. These are some consequences that might arise from extreme heat:  

• heat cramps, which often arise following exercise and are caused by dehydration and loss of electrolytes
• heat rash 
• heat oedema 
• heat syncope, or dizziness and fainting due to dehydration, medications, or cardiovascular issues 
• heat exhaustion, a serious condition that can evolve into heatstroke, which can be life threatening 
• overheating
• death, typically among those with preexisting cardiovascular or respiratory conditions.

When the ambient temperature is higher than skin temperature, of the four methods the human body normally has available for cooling, only sweating remains. Therefore, overheating becomes a risk for anyone who is dehydrated, wearing clothing that reduces the effectiveness of sweating, or taking certain medications. Young children, older adults, and people with certain health conditions may feel the effects of high temperature more severely than others.

Furthermore, temperatures higher than 25°C are associated with excess deaths, meaning more deaths being recorded at a population level than the average for that period. The higher the temperature, the more excess deaths occur. Many of these excess deaths are among people with preexisting cardiovascular or respiratory diseases, which the heat exacerbates. In particular, heart attacks and strokes occur more often in hot weather. 

Long-term health impacts

Over time, prolonged and routine exposure to extreme heat could lead to poor health, increased sickness absence among staff, and greater health burdens. This may be due to:

• skin cancer, several forms of which can be caused by exposure to ultraviolet (UV) radiation from the sun, with more exposure resulting in a higher risk
• eye problems such as cataracts and macular degeneration, which UV light exposure contributes to. 

Preventing heat-related health issues

To minimise the health risks associated with heatwaves, protective measures mostly revolve around keeping cool. These are some effective ways to do that: 

• Stay out of the heat: try to avoid the sun between 11.00 and 15.00, and keep sun off the skin while outside by sticking to the shade and wearing light clothing. 
• Keep your body cool: consume cold drinks and food, avoid excess caffeine and alcohol, and take cold showers or sprinkle your clothes with cold water.
• Keep your environment cool: monitor your environment’s temperature, use shading, insulate your spaces, keep plants if possible, and turn off any non-essential electrical equipment.
• Look out for others, particularly young people and older adults, and know the signs of heat-related illness.
• Wear suncream, light clothing, sunglasses, and a shading hat to avoid the damage that UV radiation causes to the eyes and skin.

Hot weather has been linked to temporary reductions in cognitive ability, increased workplace accidents, and increased aggression. The precise nature of these relationships is not fully understood due to the number of confounding factors involved with studying this link in real-world situations. However, research to date shows a clear need for rail to understand this link and implement mitigative measures to protect staff and passengers. 

Aggression

Both laboratory and real-world studies have found a link between hotter weather and increased aggression. In laboratory conditions, people in hotter rooms perceived others to be more aggressive, and they responded to situations more aggressively themselves. Meanwhile, studies observing real-world situations have found that violent crime increases in warmer weather. For example, London’s Metropolitan Police have reported that, between 2010 and 2018, violent crime was 14% higher when the temperature was above 20°C than when it was below 10°C. Furthermore, a 2019 study conducted in South Africa found that definite homicides were 1.5% more common for every degree higher the day’s maximum temperature was.²

Lots of factors could contribute to this increase, and while most studies control for a few of those factors, more research is needed to understand exactly what causes this relationship. It probably has multiple components: 

• Feeling uncomfortably hot could shorten people’s tempers.
• People are more likely to leave their homes in hot weather, creating more opportunities for assault.
• More events happen in the summer, and people spend longer periods outside drinking alcohol.
• Infrastructure might fail during hot temperatures, leading to disruption and subsequent aggression among those affected.

Only a minority of people who travel on the network are aggressive to staff and other passengers. However, it is worth mentioning that issues such as signal failures and buckled rails—which do occur more often during extreme heat—can cause delays and have the potential to perpetuate aggressive tendencies in those already predisposed to them, especially on very hot, bothersome summer days.   

No one should face abuse or violence on the rail network. Finding ways to prevent excessively hot environments and the risks—both direct and indirect—they can bring to staff and passengers is very important. We can look at data about incidents on the network to identify weather-related hazards or situations where the risk of violence is likely to be higher than normal. We could then respond to these insights by deploying measures such as reducing crowding at those times, handing out free water above certain temperature thresholds, and liaising with the British Transport Police. RSSB already studies work-related violence and will consider the role of extreme heat in upcoming work. 

Cognitive impairment

There also seems to be a link between higher temperatures and worse performance on cognitive function tests. However, research on this subject is difficult to draw solid conclusions from because of how much variation there is in the methods used to try to quantify this link in scientific literature. The measures of cognitive performance tested, the people who participated in the studies, the humidity, the duration of exposure, the hydration level of the participants, and the study design all vary so much that while ‘heat reduces cognitive ability’ is stated as fact in both scientific and mainstream literature, articulating to what degree and at what temperatures is very difficult. 

Evidence supporting this link looks at associations between high temperatures and worse performance on cognitive tests measuring reaction time, attention, and productivity.³,⁴ One study of workers at a casting plant showed they made more errors and performed worse on cognitive tests above a 32.9°C ‘wet bulb globe temperature’, which is a measure of how hot situations feel to those in them, taking into account humidity, wind, and the actual temperature. Similar results have been described when studying soldiers in deserts.⁵ The effect is more significant when more complex tasks are concerned. Factors thought to contribute to this effect include discomfort, cognitive fatigue, and sleep disturbances, all of which are believed to reduce people’s capacity to process task-related information and are known to happen when people are too warm. 

Additionally, a study that investigated how long bus drivers could safely operate for in hot weather in China found that, based on measures of physiological stress and reaction times, the safe driving times for drivers operating at 32°C, 36°C, and 40°C were 80 minutes, 73 minutes, and 53 minutes, respectively.⁶ The study authors suggested that safe driving times could be prolonged by making several behavioural and environmental modifications, including drinking water often, increasing ventilation, and wearing cool clothing. The physical fatigue that can result from working outdoors in hot weather has been shown to make those experiencing it more prone to safety and health risks, making accidents at work more likely.⁷

It is difficult to determine from the literature under what conditions heat should start to be a concern for people performing safety-critical tasks on the railway. This is due to the different situations these studies investigate and because individual differences probably play a significant factor in the heat levels that different people can tolerate. Cognitive impairment can also be a direct result of dehydration, for example, which is more common in hot weather.

Studies investigating dehydration and cognitive functioning have some of the same problems as studies investigating the link between cognitive function and heat. While the results of individual studies vary considerably and are hard to compare, dehydration has been shown to lead to impairments in memory, numerical ability, psychomotor function, attention, and perception. People self-report that dehydration can negatively impact their mood, alertness, concentration, and tension and cause fatigue. A review of literature on this topic found that evidence generally supported the notion that dehydration leads to cognitive impairment—but like research on heat, it could not give precise details of the strength and characteristics of this link.⁸

Fortunately, dehydration is relatively easy to manage in the UK; people just need to drink enough water and implement measures that reduce water loss from sweating, such as seeking shade and wearing appropriate clothing. ‘Voluntary dehydration’, where people choose not to drink enough water, is a very common problem. People might become ‘voluntarily’ dehydrated because they underestimate the amount of water they need to drink, because they don’t have easy access to sufficient water, or because they have limited opportunities for bathroom breaks, among other factors. 

Educating people about the amount of water they need, and removing barriers to their consuming enough water, can reduce the prevalence of voluntary dehydration in the workforce. Providing adequate welfare facilities is key to this, and it’s something the industry is already working on with RSSB’s assistance.⁹ Messaging that includes both the health consequences for the individual and the dangers that their voluntary dehydration could pose to coworkers during safety-critical work could be particularly effective. Similar messaging about the importance of keeping cool could be useful to help people be more mindful of how they are thinking and behaving when it’s hot—whether they feel fatigued, feel they aren’t thinking clearly, or feel more frustrated and aggressive. RSSB’s research and guidance around fatigue could also be helpful in dealing with heat, as cognitive impairments resulting from heat and fatigue might be similar, or directly linked, during heatwaves.

Hot weather can also negatively impact air quality. Ozone, for instance, is a pollutant that forms more readily at ground level during sunny weather, as sunlight is necessary for its production. The interaction between sunlight and other chemicals in the air—such as nitrogen oxides from vehicle exhausts—can cause dangerous amounts to collect, beginning in cities and then spreading to rural areas.⁹ In the 2022 heatwave, the UK saw levels of ground-level ozone that exceeded the World Health Organization’s (WHO’s) safe guidelines. 

During hot weather, the air is stiller. So, in areas like cities, where a lot of air pollution in the form of particulate matter is created, the still air prevents it being cleared away. This leads to a buildup of pollutants. The makeup and distribution of different pollutants also appears to change in hot weather, with a higher proportion being organic matter and black carbon in the heatwave of 2022. Organic matter pollutants have worse health consequences than non-organic pollutants when inhaled. In hot, dry weather, dry soil increases dust inhalation, and dry vegetation can cause wildfires, which have significant health impacts on those who inhale their smoke.¹⁰

Outdoor workers, people with asthma, children, and older adults are particularly susceptible to health problems caused by exposure to pollutants in the air. Ozone, in particular, can cause airway inflammation and damage, make lungs more susceptible to infection, and aggravate existing respiratory conditions. Children are particularly vulnerable because their lungs are still developing, because they are generally more active than adults while outside, and because asthma is more common in children. 

The UK has air quality monitoring systems to warn us when pollution levels are high. However, having a better understanding of the makeup of that pollution and its implications for people working on or using the railway could help us improve our protection efforts. RSSB does extensive air quality work to understand why pollution may be worse on some areas of the network than others, and where these areas are. Overall, rail does have a positive effect on the communities it serves in terms of air quality, as it provides a less polluting alternative to private vehicles.

Longer, drier summers bring an increased risk of wildfires, which we are now seeing in parts of Europe. For our rail network, miles of which are lined by vegetation on land owned by the railway, fires represent a serious health and safety risk to people nearby. Globally, extreme fires are projected to increase by 14% by 2030, and researchers have identified wildfires as an emergent risk for the UK.¹¹

In 2020, prolonged hot, dry weather led to serious wildfires in Australia. And beyond the immediate destruction and loss of life caused by the fires, nearby communities are now seeing a range of health issues emerging that were caused by smoke inhalation. Heart failure, lung disease, muscle weakness, and speech impairment cases have increased. Inhalation of smoke, poisonous gases, and small particulate matter from the fires has contributed to approximately 400 deaths. Several years on, there is also mounting evidence that pregnancies at the time were more prone to complications, and that children who were in utero during the fires are now experiencing poor health and lung development issues. These emerging long-term health impacts demonstrate the grave risk to public health created by wildfires, which necessitate robust plans to prevent them.

In the UK, Network Rail manages vegetation along the lines carefully to minimise the risk of wildfires. They do this by selecting and locating vegetation in accordance with the Forestry Commission Practice Guide on Building Wildfire Resilience into Forest Management Planning. As the risk of fires increases, however, the network should be open to adopting new research about how to minimise the health risks that fires pose to people nearby. The WHO intends to release a report soon about the impact of fires on public health and what steps communities can take to protect themselves.