Abstract

Background

Heatwaves are hot weather events, which breach regional or national thresholds, that last for several days. They are likely to occur with increasing frequency in some parts of the world. The potential consequences were illustrated in Europe in August 2003 when there were an estimated 30,000 excess deaths due to a heatwave. Electric fans might be used with the intention of reducing the adverse health effects of a heatwave. Fans do not cool the ambient air but can be used to draw in cooler air from outside when placed at an open window. The aim of the fans would be to increase heat loss by increasing the efficiency of all normal methods of heat loss, but particularly by evaporation and convection methods. However, it should be noted that increased sweating can lead to dehydration and electrolyte imbalances if these fluids and electrolytes are not replaced quickly enough. Research has also identified important gaps in knowledge about the use of fans, which might lead to their inappropriate use.

Objectives

To determine whether the use of electric fans contributes to, or impedes, heat loss at high ambient temperatures during a heatwave, and to contribute to the evidence base for the public health impacts of heatwaves.

Search methods

We sought unpublished and published studies that had been published in any language. The review team were able to assess studies reported in English, Chinese, Dutch, French and German; and reports in other languages would have been translated into English as necessary. We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, CINAHL, the Indian biomedical literature (IndMED and MedIND) and databases of Chinese literature (Chinese Journal Net and Digital Periodical of WanFang Data). The most recent electronic searches were done in April 2012. We also checked the reference lists of relevant articles and the websites of relevant national and international organisations, and consulted with researchers and policy makers with experience in strategies to manage heatwaves to identify additional studies. The titles and abstracts from each search were checked independently by two review authors. The full text articles that we retrieved were checked independently by at least two authors for their relevance and for references to potentially eligible studies.

Selection criteria

Randomised trials and other experimental designs, such as interrupted time series and controlled before‐and‐after studies, comparing the use of electric fans with no fans during a heatwave were eligible for this review. The electric fans could be hand‐held (battery operated), portable or mounted on the wall or ceiling, or in a window. We sought interventions delivered to anyone for whom a heatwave was likely to have serious adverse health impacts. This would include people of all ages but with a particular focus on some groups (for example older people). Populations from high‐, middle‐ and low‐income countries were eligible for the review.

Data collection and analysis

If we had identified eligible studies, they would have been assessed independently by at least two review authors and data would have been extracted on the characteristics of the study, its participants and interventions, as well as the effects on health outcomes. The primary outcomes were mortality, hospital admission and other contacts with healthcare services.

Main results

We did not identify any eligible studies despite the extensive searching and correspondence with several experts in this topic area. We identified retrospective, observational studies, usually with a case‐control design, that investigated the association between the use of electric fans and health outcomes, including death. The results of these studies were mixed. Some studies found that the use of fans was associated with better health outcomes, others found the reverse.

Authors' conclusions

The evidence we identified does not resolve uncertainties about the health effects of electric fans during heatwaves. Therefore, this review does not support or refute the use of electric fans during a heatwave. People making decisions about electric fans should consider the current state of the evidence base, and they might also wish to make themselves aware of local policy or guidelines when making a choice about whether or not to use or supply electric fans. The main implication of this review is that high quality research is needed to resolve the long standing and ongoing uncertainty about the benefits and harms of using electric fans during a heatwave, for example randomised trials comparing the health effects in people with electric fans to those in people without them.

Author(s)

Saurabh Gupta, Catriona Carmichael, Christina Simpson, Mike J Clarke, Claire Allen, Yang Gao, Emily Y Y Chan, Virginia Murray

Abstract

Plain language summary

Electric fans for reducing the health effects of heatwaves

Heatwaves are set to become more common and their effects can be devastating. For example, up to 30,000 people may have died because of the heatwave that occurred in Europe during August 2003. One way to try to get relief from the heat is to use an electric fan, but whether this will do more good or harm is uncertain. A fan might help to increase heat loss if the temperature is below 35 °C and the fan is not directly aimed at the person, but, when temperatures are above 35 °C, the fan might actually contribute to heat gain. Excess sweating can also lead to dehydration and other health problems. It is important, therefore, to know about the potential benefits and harms of electric fans when choosing whether to use one. This applies if the decision is about your own use of a fan, but it is also relevant to broader public health decisions, such as whether to give electric fans to groups of people during a heatwave. This is particularly important for people who are considered more vulnerable to the effects of heat, such as older adults who are less able to cool down through sweating or increasing the flow of blood to their skin.

This Cochrane Review tried to provide some of the answers that would help decision makers. We looked for high quality research that had compared groups of people using fans with groups who didn't use them during a heatwave However, we didn't find any research that met our requirements. We did find some studies which used designs that are less reliable for answering this sort of question, and these had mixed results. Some suggested that fans might reduce health problems, while others suggested that the fans might make things worse.

Therefore, the research that has been done to date does not resolve uncertainties about the health effects of electric fans during heatwaves. People who have to make decisions should consider the current evidence, alongside local policies and guidelines when making their choices. They may wish to help resolve the continuing uncertainty by conducting the type of high quality research that would provide the reliable evidence needed to determine the benefits and harms of using electric fans during a heatwave.

Author(s)

Saurabh Gupta, Catriona Carmichael, Christina Simpson, Mike J Clarke, Claire Allen, Yang Gao, Emily Y Y Chan, Virginia Murray

Reviewer's Conclusions

Authors' conclusions 

Implications for practice 

In light of the lack of any eligible studies for this review and the uncertainties around the effects of electric fans in the observational studies that we identified, and the potential for harm as well as for benefit in their use, this review does not support or refute the use of electric fans during heatwaves. People making decisions on their own behalf, on behalf of others or for inclusion within local or national guidance and policies should consider the current state of the evidence base when making a choice about whether or not to use or supply electric fans.

The main implication of this review is that research is needed to resolve the long standing and ongoing uncertainty about the benefits and harms of using electric fans during a heatwave. Therefore, decision makers and policy makers may wish to help resolve this uncertainty by encouraging and conducting the type of research that is needed to measure reliably the benefits and harms of using electric fans during a heatwave. Any findings of future research in this area would have potential implications not only for individuals, but also have significant influence on the evidence base on which policy (local, national and international) is based. Such research findings would serve to potentially strengthen national heat wave plans and health care guidance. Public health professionals may wish to give details regarding the potential benefits and disadvantages of using an electric fan during a heatwave, to help individuals make informed decisions regarding their use.

Implications for research 

The need for research to resolve the ongoing uncertainties about the potential beneficial and harmful effects of the use of electric fans during heatwaves was highlighted by several of the studies that we found, but which were not eligible for this review because of their study design. For example, Semenza et al wrote “The effectiveness of fans in preventing death during periods of high heat and humidity remains a matter of controversy and deserves further attention” (Semenza 1996); and Bouchama et al drew the general conclusion that “other common recommendations, such as using a fan, drinking extra water, taking extra showers, and reducing outdoor activities, would need further evaluation, particularly as they are not without potential adverse effects” (Bouchama 2007). We obtained similar views from our correspondence with various international organisations as well as policy makers across the world.

No reliable evidence to estimate the effects of electric fans during heatwaves has been found for this Cochrane Review. Such evidence could be generated by an appropriate randomised trial in a naturally occurring heatwave of electric fans versus no fans within the general adult population of an area, but with a focus on older people, measuring outcomes such as heat‐related morbidity and mortality. We have, therefore, suggested the design for one such trial using the framework proposed by Brown et al (Brown 2006). This design has been provided as an outline only and the details would need to be adapted to the area in which any such a study is undertaken. Furthermore, studies of this topic might adopt similar methods to those used in studies to determine the effects of smoke alarms in residential settings (DiGuiseppi 2001).

We recognise that there are some characteristics of such a study which would make it particularly challenging. For example, the unpredictable nature of extreme events such as heatwaves, where the researchers would need to adopt a watch and wait approach with the trial and the necessary resources being ready to activate, potentially for several years. Examples already exist of such plans, for example in a series of studies funded by the National Institute for Health Research in the UK which will be activated in an influenza pandemic and the work of the International Severe Acute Respiratory Infection Consortium (ISARIC) (Yong 2012).

It would also be important to ensure that any recommendations on interventions to be used, either alongside the electric fans or as a comparator, are evidence‐based. This systematic review has not assessed the evidence behind any of the other interventions used in heatwaves and even where evidence is available the comparisons would have to be done carefully. For example, a comparison of the effects of electric fans versus air conditioning on health and environmental impact would be dependent on the context of their use, particularly in terms of the comfort temperature requirements of the occupants, the level of heat gain in the space and zoning. Air conditioning energy use may be affected by choice of local or multiple room systems, or their unintentional combination via doors and stairways, the outside air heat rejection temperatures coincident with operation, and the selection and appropriate setting of controls for comfortable temperatures and operating periods. The comparison with air conditioning is therefore not straightforward due to the variations in system choice and method of operation. Comparisons may also need to consider the ability of fans to manage high internal heat gain and noise generation issues.

Another challenge might be to ensure that all important aspects of the atmosphere (meteorological conditions such as wind speed, humidity, temperature inside various rooms, insulation of building, placement of doors and windows, etc) can be measured and reported accurately, reliably and consistently to show that any effect attributed to the electric fans is not affected by confounding by any other factor.

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