One summer too many: the story of a HR director at 39°C

It's 4:12pm on July 18, 2024. Julie, HR Director of an industrial SME in the South-West of France, watches the hygrometer panic: 39°C in the open-plan office, 61% humidity. The air conditioning has just stopped.
In the space of forty-five minutes, she has to manage :

• a clash of voices between two team leaders over a trivial schedule;

• a data entry error that erased two days of customer orders;

• three vagal discomforts, one of which required the intervention of the fire department;

• seventeen angry e-mails demanding fans "immediately".

As Julie steps out into the parking lot, which has become a frying pan, she realizes that heatwave, or heat stress, is no longer just a hydration issue: it's a psychosocial risk. This phenomenon can undermine team cohesion, impair cognitive performance and exacerbate psychosocial risks within the organization.

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When she alerted her executive committee, the first response was: "We've had worse! Three weeks later, the HR indicators speak for themselves: absenteeism +14%, quality errors +19%, customer satisfaction -8%.

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That day, Julie vowed to include temperature in her QVCT action plan, to prevent heat-related psychosocial risks. Her story is not an isolated one: it illustrates a silent shock that is already hitting many European companies.

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1. Why does heat affect our brains?

1.1 Thermoregulation vs cognition: the energy duel

The brain accounts for 2% of body weight, but up to 20% of energy expenditure. When body temperature rises, the hypothalamus triggers a vast emergency plan to maintain life: vessels dilate, sweat and the heart speeds up. This mechanism mobilizes glucose and oxygen to the detriment of so-called "higher" functions. Result:

• Loss of working memory: remembering instructions for more than ten seconds becomes an effort.

• Decreased processing speed: every decision takes longer, especially complex, multi-dimensional ones (crisis management, budget arbitration, negotiation).

• Executive fog: planning, prioritizing, inhibiting impulses is more difficult.

According to a report by the International Labour Organization (ILO), working in temperatures above 24-26°C slows productivity. Above 30°C, productivity drops by half (Oxfam report). Productivity losses vary according to the activity. But the most striking statistic is qualitative: social tolerance melts as fast as the mercury rises.

1.2 Fragmented sleep, heightened anxiety

Tropical nights prevent the thermal drop essential for deep sleep cycles.  

The World Meteorological Organization (WMO) warns that tropical nights (very high temperatures at night) increase the number of nocturnal awakenings and, in particular, reduce deep sleep, essential for recovery.

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A study published in the journal Nature, and carried out by a team of Chinese researchers, shows that when the temperature rises by 10ºC, the duration of sleep over one night decreases by 9.67 minutes, particularly deep sleep.

There's also an increase in cortisol (stress hormone) on awakening, and a drop in empathy.

Sleep deprivation accentuates irritability, anxiety and depressive symptoms. It's the fuel for a vicious circle: a hot day sets the stage for a bad night, which sets the stage for a new, even more vulnerable day.

1.3 Heat and mood

Prolonged exposure to 32-35 °C may result in :

• greater sensitivity to social stressors;

• an increase in rumination (the tendency to dwell on problems);

• an increase in accidental risk-taking (driving, using machinery).

In other words, heat is not just a source of discomfort, it's a biological modulator of our emotions and behavior.

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2. Heat at work: psychosocial consequences

2.1. Heat and tension in open spaces: why incivilities are soaring

Field studies have shown that a tense climate - in the meteorological sense of the word - is a breeding ground for incivilities (abrupt interruptions, disparaging remarks, raising one's voice...).

The mechanism is simple: the ability to deal with negative emotions diminishes, social filters break down, and immediate impulses are unleashed. The equation becomes explosive if pre-existing tensions (high targets, restructuring, overload) are already present.

2.2 Human errors and hasty decisions

Heat can have an impact on all activities. In support departments, for example, we can see e-mails sent without proofreading, important meetings cancelled, and back-ups forgotten. In other professions, we may see an increase in product non-conformities, for example. Heat causes a cognitive let-go, often underestimated because it is perceived as harmless.

2.3. De-motivation, disengagement and latent attrition

Long-term, persistent heat can hamper commitment to work. Employees may feel a sense of injustice if company management has made no provision to counter the heat. This can lead to a loss of meaning: "Why make so much effort if we're left in this heat? The risk of leaving the company is then present.

3. Corporate heat: legal, HR and reputational risks

3.1 What are the legal requirements for heat in the workplace?

The French Labor Code (art. L.4121-1) requires employers to take "the necessary measures to ensure the safety and protect the physical and mental health of workers".

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The "heat risk" decree of May 2025 extends the obligation to include heat waves in the DUERP, and provides for graduated alert levels based on weather vigilance. In the building and civil engineering sector, the "heatwave unemployment" scheme provides compensation for employees affected.

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For management, ignoring the heat factor therefore becomes a criminal risk (aggravated workplace accident) and a social risk (strikes, impact on image).

3.2. The reputation equation

The new generations are particularly attached to the values of health and ecology. A company singled out for letting employees "cook" will be perceived as negligent. Social media can turn a photo of an overheated warehouse into an employer brand crisis in a matter of hours.

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4. Preventing heat at work: practical strategies for HR, managers and QHCT officers

4.1. 5 immediate actions to protect your employees during heat waves

• ‍Staggered shifts: open business between 7am and 2pm during orange/red peaks. This will reduce the risk of errors and improve employee satisfaction. ‍
• Targeted teleworking: allow teleworking for analytical tasks. ‍
• Cool-down breaks : 10 min/hour in a room with a maximum temperature of 26°C. Install a simple mobile air conditioner, water fans or, better still, share an air-conditioned server room.
• ‍Active hydration: refrigerated fountains, "1.5 l/day" challenge.
• ‍Adapted dress code: maintaining decency, allow lighter fabrics, allow open shoes in non-industrial departments.

4.2 Managerial training: from thermometer to emotional barometer

• Awareness: how heat affects the prefrontal cortex; recognizing weak signals (micro-aggressions, reduced attention, lengthened gestures).

• Inner Weather" workshops: at the start of each meeting, each participant expresses his or her feelings between 1 (ice) and 5 (boiling). This ritual replaces sighing with verbalizing, reducing tensions before they explode.

• Express regulation techniques: cardiac coherence (5 min), micro-naps, cold visualization (imagine a polar landscape).

4.3. Organizational adaptation scenarios

Other actions can also be implemented:

• Short-term: thermal audit of premises, heatwave emergency plan, internal alert protocol (SMS, Teams).

• In the medium term: work to reduce heat: solar films, external blinds, "cool roofs", facade greening, mobility plan (avoid overcrowded transport).

• Long-term: bioclimatic overhaul: orientation of new buildings, geothermal energy, Canadian wells, CSR Climate & Mental Health policy.

4.4 Integrating the heat dimension into the QVCT plan

• ‍Heat/RPS key indicators: measure temperature/conflict/error/stop correlation in real time. ‍
• Decision matrix: define HR, HSE (health, safety, environment) and IT measures for each threshold (yellow, orange, red) (e.g. Limit meetings longer than 30 min, force automatic backups). ‍
• 24/7 psychological assistance cell: listening and support line, triggered at the orange threshold: emotional support, redirection to the occupational physician, managerial advice. ‍
• Positive communication: internal newsletters "Keeping a cool head", infographics, "Your fresh break" photo challenges.

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5. Conclusion - Regaining control of your indoor climate

Heat waves are no longer the exception. They are the new backdrop to our working summers. To ignore their psychological influence is to accept a productivity deficit, rising tensions and a legal risk.
Conversely, to anticipate, train and adapt is to turn a climatic phenomenon into a competitive advantage:

• closer-knit teams because they feel protected;

• a pioneering employer image for mental health;

• a more resilient, energy-efficient organization.

Like Julie, every HR person has the power to put warmth on the COMEX agenda, to mobilize collective creativity, to build an environment where the internal temperature - physical and emotional - remains conducive to fulfillment and performance.