Thousands of migrant construction workers employed on huge infrastructure and building projects ahead of next year’s Expo 2020 exhibition in Dubai are likely to have been exposed to dangerous levels of heat stress, a Guardian investigation has found.

Dubai will host the Expo 2020 next year, in which 190 countries will come together to celebrate themes of mobility, innovation and sustainability in a series of bespoke, themed pavilions across a 4.38 sq km site in Dubai South economic zone.

Yet a Guardian investigation has found that migrant workers who have been building the infrastructure, accommodation blocks and national pavilions across the summer months could have been working in unsafe and potentially fatal conditions.

Construction work for the Expo 2020 began in 2015 and British construction firms including McLaren and Laing O’Rourke are among dozens of foreign companies involved in multi-million-pound construction projects for the global exhibition. To date, 60% of the Expo work has already been completed.

The United Arab Emirates is a dangerous place for the hundreds of thousands of migrant labourers who travel from their homes in India, Nepal, Pakistan and Bangladesh to work in the heat and dust of one of the wealthiest countries in the world.

Every year hundreds of workers – mostly young men – who have travelled from India, Nepal, Pakistan and Bangladesh, die while working in the Gulf state.

Worker fatality numbers are difficult to access, but according to data from the Indian government, 5,185 Indian nationals died between 2012–2017. Many of these deaths are recorded as cardiovascular events such as respiratory failure, cardiac arrest or “natural deaths”. Of the 126 “blue collar” workers the Indian government said died in the UAE last year, 70% were recorded as dying from heart attacks.

Heat places a huge strain on the cardiovascular system with extreme heat stress leading to potentially fatal heart attacks and other cardiovascular failures.

Recent research by cardiologists and climatologists concluded that exposure to extreme heat stress was linked to the deaths of hundreds of Nepali migrant workers in Qatar, which has similar weather conditions to the UAE.

The authorities in the UAE, in line with other countries across the Gulf, has said they are protecting workers from heat-related injuries through a work ban that prohibits manual labour in unshaded outdoor areas between 12.30–3pm from June–August.

However the Guardian’s weather analysis found that the summer work ban in the UAE does not keep workers safe. Anyone working outside who is performing even moderate physical labour is exposed to potentially fatal levels of heat stress for the majority of the working day from June–September every year.

British companies McLaren and Laing O’Rourke are currently working on Expo 2020 projects.

The UK’s Department for International Trade awarded the £21m contract to build the UK Expo 2020 pavilion, which is inspired by Stephen Hawking’s “breakthrough message” initiative, to Pico and McLaren. McLaren is also working on construction at Dubai airport.

Laing O’Rourke is working on a contract to build the Leadership and Media pavilions, as well as the “Hammerhead” access road to the central event space for Expo 2020 Dubai.

The companies said that they have robust heat strategies in place that go above and beyond the 12–3pm summer work ban imposed by the UAE government.

McLaren said that construction work on the UK pavilion is being timed to coincide with cooler temperatures. It also has detailed heat mitigation measures in place including chilled welfare areas, shaded rest areas on site and amended work schedules based on expected heat levels.

Laing O’Rourke said that it had specific summer working policies in place and well-defined procedures on how to implement these measures.

UK non-profit organisation the Business and Human Rights Resource Centre (BHRRC) said that a survey it conducted of construction companies operating in the UAE last year found that many did not have robust heat monitoring programmes in place.

“Although British companies are doing comparatively well at taking the issue of heat stress seriously compared to many of their peers, all international construction companies in the UAE operate with an unacceptable level of risk to their workers,” said Diana Eltahawy, Gulf programme manager at BHRRC.

The glamour of Expo 2020’s design contrasts with the conditions endured by constructors. Photograph: Expo 2020

The Guardian used weather data from 2008–2017 to calculate the wet-bulb globe temperature (WBGT) for UAE, an internationally used metric that uses wind speed, solar radiation, humidity and air temperature to assess the impact of heat stress on the human body.

A WGBT reading of 28C (82F) and above is internationally accepted as the point at which the human body is dangerously affected by heat stress.

The analysis found:

In July, despite the work ban, anyone working outside will have been exposed to dangerous levels of heat stress between 9am-9pm. Between 9am-3pm workers can only safely work outdoors in unshaded areas for a maximum of 15 minutes an hour for almost every day of the month.

In June, heat stress exposure was at a dangerous level between 9am–6pm. Before the outdoor working ban came into effect on the 15th, no work at all could be done safely between 9am and 3pm.

In August, anyone working outside was at risk of suffering from dangerous levels of heat stress between 9am-6pm for the entire month. For most days between 9am–3pm, workers should have been working a maximum of 15 minutes an hour.

The second half of September, after the end of the outdoor work ban on the 15th, was particularly dangerous. Virtually no work could be done safely between 12pm and 3pm and workers should have been working just 15 minute intervals between 9am and 12pm.

The first half of October was also dangerous. Between 9am and 3pm labourers should have worked for a maximum of 15 minutes an hour.

An Expo 2020 spokesperson said, “Our assurance standards require contractors to develop and implement an all-year-round ‘weather working plan’ detailing arrangements for working safely in the heat (over and above the UAE legislation on summer-time working). All contractors are required to establish calibrated project weather stations which monitor the thermal work limit, which takes into account wet-globe temperature, dry-bulb temperature, globe temperature and wind speed. Contractor plans include specific action levels and arrangements to be undertaken at each level. Our working in the heat policies, procedures and associated arrangements apply throughout the year and we run courses and programmes to support them.”

The UK’s Department for International Trade said: “DIT has taken a series of measures to ensure high health and safety standards are maintained for all workers at the UK pavilion at Expo 2020 Dubai site.”

The United Arab Emirates government did not respond to requests for comment.