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Journal of Public Health Advance Access originally published online on September 11, 2008
Journal of Public Health 2008 30(4):391-397; doi:10.1093/pubmed/fdn073
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© The Author 2008, Published by Oxford University Press on behalf of Faculty of Public Health. All rights reserved

Review of acute chemical incidents involving exposure to chlorine associated with swimming pools in England and Wales, June–October 2007



H. Lucy Thomas, Specialist Registrar in Public Health

Virginia Murray, Head of Unit and Consultant Medical Toxicologist
Chemical Hazards and Poisons Division (London), Health Protection Agency, London WC1V 7PP, UK

Address correspondence to H. Lucy Thomas, E-mail: lucy.thomas{at}hpa.org.uk

Background Acute chemical incidents involving chlorine have potentially important public health consequences. Swimming pools are the single most common setting for such incidents in the UK. This study systematically describes the distribution, characteristics and public health consequences of all acute chemical incidents associated with swimming pools in England and Wales over a 5-month summer period.

Methods All chemical incidents occurring from June to October 2007 reported to the Health Protection Agency or identified through media reports were included. Standardized information on the incidents was collected from local Health protection units, emergency services and/or local authorities.

Results In the study period, 13 incidents were identified. In many of the incidents, evacuation and dispersal of those involved occurred before the arrival of emergency services and some individuals self-presented to clinical services. During the study period, no individuals suffered from severe health effects due to chlorine exposure.

Conclusions Acute chemical incidents associated with swimming pools are relatively common and can lead to the evacuation of large numbers of people even when the release is confined to the pool plant room. The evacuation and dispersal of wet, poorly clad swimmers may have negative health consequences. Incident management protocols should include consideration of when full pool evacuation is justified and mechanisms to ensure the correct advice is available for affected individuals.

Keywords: chemical hazards, health protection


   Introduction
TOP
 Introduction
Methods
 Results
 Discussion
 Acknowledgements
 References
 
Chlorine and chlorine derivatives are widely used in industry, with 55 percent of Europe's overall chemical production being directly or indirectly dependent on chlorine.1 Chlorine is a highly toxic gas that causes severe irritation to the mucous membranes and respiratory tract at concentrations as low as 5 ppm, with toxic pneumonitis and pulmonary oedema developing at levels >30 ppm.2 In addition to these acute symptoms, acute inhalation exposure can lead to a chronic reduction in forced expiratory volume. Acute releases of chlorine thus have substantial public health consequences, leading to the evacuation of buildings, acute and delayed respiratory symptoms and potential loss of life.3 Recent chlorine gas attacks in Iraq4 have raised concerns about the potential use of chlorine as an agent in a deliberate release.5

From 2003 to 2006, 56 incidents involving the acute release of chlorine were reported to the Health Protection Agency (HPA) in England and Wales [HPA Chemical Hazards and Poisons Division Surveillance System (CHaPD) for Chemical Incidents] (unpublished data). These incidents occurred in a variety of settings, but the single most common setting involved (accounting for 34% of incidents) was in swimming pools. Similarly, in a series of chlorine-related incidents reported to the British Health and Safety Executive from 1992 to 1998,6 incidents associated with swimming pools accounted for the largest proportion (22%) of the 59 incidents reported.

Owing to their capacity to oxidize organic substances, chlorine-based products (such as sodium hypochlorite, calcium hypochlorite and chloroisocyanurates) are the most common disinfectants used in swimming pools.7 Inadvertent contact between these chemicals and the acids used for regulating the pH of pool water will lead to the production of chlorine gas.8 Although such chemicals are stored separately, and often introduced into the water using an automatic dosing system, the co-location of these chemicals in swimming pool plant rooms leads to the potential for inadvertent mixing due to mechanical or human error.

In the published literature of the past two decades, there have been a number of individual reports on the clinical consequences of acute chlorine exposure incidents at swimming pools.9–17 In one of these incidents,11 116 people were taken to hospital and persistent respiratory symptoms and impaired lung function were found in 25 patients up to one month after the incident. Four of the incidents resulted in patients requiring intensive care management9,13,15 and, in one incident, a patient died following accidental exposure to pool chlorinators.9

The only previously published study of a series of such incidents reports on six swimming pool chlorine intoxication incidents occurring in Israel in the summer of 2005.18 This study found that although there were a total of 80 patients (range 4–40 years) associated with the six incidents, the vast majority (78) had mild or mild-moderate symptoms, with only two suffering from symptoms of moderate severity. Information on the source of the event and its public health management is only provided for one incident.

These previous reports provide useful documentation of the potential clinical consequences of acute chlorine exposure. However, as they have a predominantly clinical focus, they provide a limited picture of the public health management and consequences of such incidents. In addition, with the exception of the Israeli study,18 they only report on incidents with important clinical consequences, and therefore do not provide an overview of the frequency and severity of acute chemical incidents associated with swimming pools. The aim of this study was to systematically describe the distribution, characteristics and public health consequences of all acute chemical incidents related to swimming pools in England and Wales over a 5-month period to identify key health protection issues around their management.


   Methods
TOP
 Introduction
 Methods
Results
 Discussion
 Acknowledgements
 References
 
The study aimed to capture all chlorine-related chemical incidents involving swimming pools in England and Wales occurring over a 5-month period from June to October 2007 (inclusive). This time period was chosen as such incidents are more frequent in the summer months, with >70% of incidents occurring between May and October in the years 2005 and 2006 (HPA, unpublished data). Four partially overlapping sources of information were used to identify these incidents:

  • The CHaPD Surveillance System for Chemical Incidents at the HPA, which receives information from a wide number of governmental and non-governmental sources19
  • The London Chemical Incident Early Alerting System, which ensures that the HPA is informed of acute chemical incidents involving the emergency services in London20
  • An HPA national briefing note21 informed all local Health Protection Units (HPUs) and HPA regions of the study and asked them to inform CHaPD London of all chemical incidents related to swimming pools during the study period
  • A weekly media review of the BBC news website, on-line local newspaper and other news agencies websites, and a news cutting service from national newspapers was used to gather relevant stories that had not been reported to the HPA.22
A questionnaire was developed for collecting systematic information on all the incidents identified. Following the identification of an incident that fulfilled the inclusion criteria, a member of CHaPD contacted the local HPU for further information in the first instance. Additional information was collected from the ambulance service, the fire service and the local authority if appropriate, either directly or via the local HPU.


   Results
TOP
 Introduction
 Methods
 Results
Discussion
 Acknowledgements
 References
 
Summary of incidents
In the 5-month period (June–October 2007), there were 11 acute chemical incidents related to swimming pools reported to CHaPD. An additional two incidents were identified from a trawl of local media, giving a total of 13 incidents that were identified as having occurred during the study period. A summary of these incidents is provided in Table 1.


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  		Table 1 Summary of acute chemical incidents associated with swimming pools, England and Wales, June–October 2007

 
Causes of incidents
The most common causes of chemical release in the incident were chemical tank or pipe leaks (responsible for five (42%) of the incidents), followed by the incorrect mixing of chemicals (responsible for four (33%) of the incidents) (Table 1). Sodium hypochlorite was one of the chemicals involved in all 10 of the incidents for which specific chemical information was available. This was mixed with an acid (hydrochloric acid or sulphuric acid) in three incidents, and combined with sodium bisulphate in two incidents, resulting in the release of chlorine gas.

Evacuation
Information on the specific location within a pool or leisure centre complex from which individual(s) were evacuated was hard to obtain because evacuation and dispersal occurred before the arrival of the emergency services.

Information on the number of people evacuated during the incident was available for 7 of the 13 incidents:

  • In two of the incidents involving chemical release at a domestic swimming pool, no evacuation was carried out;
  • For the two incidents occurring in commercial health club swimming pools, in one incident only one person was evacuated (the only person in the pool at the time) and in the other incident approximately 100 people were evacuated;
  • In the incident at a school swimming pool, 210 people were evacuated;
  • In two incidents that occurred in large local authority pools, 10 and 18–19 people were evacuated, respectively.
For the remaining six incidents, it was not possible to obtain information on the number of people who had been evacuated as evacuation without documentation occurred before the arrival of the emergency services. In two of these six incidents, members of the public self-presented to Emergency Departments.

Number of people with chemical exposure
In the vast majority (70%) of incidents that occurred in non-domestic settings, the incident was confined to the swimming pool plant room (see Table 1). In these incidents, only small numbers of staff entering this area were exposed to the chemicals released.

  • During two incidents, no one was exposed to the chemicals released, the plant room being secured before the arrival of the emergency services;
  • In two incidents, a single member of staff was exposed;
  • During one incident six members of staff had entered the plant room and been exposed to the chemicals released.
Two incidents occurred when concentrated doses of chemicals entered the swimming pool itself following pump failure/routine maintenance work. In one of these incidents 19 people were exposed to the chemicals, and in the other (which occurred in a commercial health club pool) there was only one swimmer in the pool at the time of exposure.

For the two incidents involving incorrect mixing of chemicals in domestic swimming pool settings, only the one person who was involved in the mixing was exposed to the resultant chemicals in each case.

Attendance of emergency services
In all but 1 of the 13 incidents, the fire brigade attended the scene. Ambulance services also attended 9 of the 10 incidents where there were persons exposed. It appears that in one incident (in which concentrated doses of chlorine entered the pool in which one member of the public was swimming), the emergency services were not informed of the incident.

Number of casualties associated with the exposure
For five of the incidents, there were no casualties.

For the remaining seven incidents, casualties were between one and nine per incident (mean 2.7). The symptoms reported were breathing difficulties (four incidents), coughing (three incidents) and nausea, vomiting, sore eyes or rash (one incident).

In only five of the incidents were any casualties taken to hospital. One casualty from each of three incidents was hospitalized; two for observation/monitoring and one due to respiratory difficulties. No information was available regarding hospitalization of casualties for the remaining two incidents.

In one of the incidents, three members of the public who were evacuated and had dispersed before the arrival of the emergency services self-presented to the Emergency Department.

Following the incident, to which the emergency services were not called, the member of the public exposed was advised by the swimming pool manager to attend hospital for a check-up. The person exposed did this and was hospitalized overnight for monitoring of breathing difficulties.

Information provided to those with chemical exposure who were not taken to hospital
In seven of the incidents, there were person(s) exposed to the chemical who did not require conveyance to hospital. For five of these incidents, the ambulance service completed Chemical Indcident Response Forms (documents recording the demographic details and potential chemical exposures of those involved) on all those exposed. In all of these incidents, information was provided to these persons on the importance of seeking medical care if delayed respiratory symptoms developed. There was no information available about whether this information was provided for the remaining two incidents.

Decontamination
At four of the incidents, decontamination of exposed persons was carried out on scene. In two of these incidents, decontamination was carried out using the pool showers. None of the incidents resulted in casualties requiring decontamination at hospital.

Exposure of healthcare workers
For all five incidents for which information is available, the healthcare workers attending exposed persons wore gloves, and for one incident they also wore aprons. There were no reports of healthcare workers developing symptoms of exposure in any of the incidents.

Post-acute respiratory syndrome
For only 1 of the 10 incidents in which there were people exposed to chlorine was there clear documentation available to show that no one had been admitted to hospital with post-acute respiratory syndrome. This information was not available for the remaining incidents.

Communication
The local HPU was informed of 11 of the 13 incidents via local emergency services or via established links between local emergency services and CHaPD. In one instance, the HPU was informed after the incident had been stood down. The local HPU was not informed of two of the incidents until reports were spotted in the local media (including one large incident with 19 people exposed and 9 casualties).

Media coverage
All the incidents that occurred in large local authority pools resulted in reports in the local print media. In addition, the incident that occurred in a school swimming pool, one of the incidents in a commercial health club swimming pool and one of the incidents related to a domestic pool were reported in the local press.


   Discussion
TOP
 Introduction
 Methods
 Results
 Discussion
Acknowledgements
 References
 
Main findings of this study
The most common cause of chemical release in the 13 incidents reported during the study period was either human error (incorrect mixing of chemicals or a chemical spill) or leakage from a chemical pipe or tank. In the majority of incidents, the chemical release was confined to a plant room. Although a large number of people were often evacuated, very few people were significantly exposed and none exhibited severe health effects.

In many of the incidents evacuation of the pool and dispersal of those involved occurred before the arrival of the emergency services and we found that information about those who evacuate early is not documented. Such dispersal could have resulted in people exposed to chlorine not receiving information about the health effects of exposure and the importance of seeking medical care if respiratory symptoms develop.

In two incidents, symptomatic individuals self-presented to emergency departments and in one of these incidents one person required overnight hospitalization to monitor respiratory difficulties.

In the majority of incidents in which chemical exposure occurred, information was available to demonstrate that appropriate documentation of exposed individuals had been carried out by the emergency services, and appropriate written or verbal advice had been provided to those persons who remained at the scene.

Decontamination of exposed individuals was only required in 4 of the 13 incidents, and for half of these the pool showers were used for decontamination.

In the majority of incidents the local HPU was informed through established early alerting links. However, two incidents were not reported to the HPU, and the HPA only became aware of these incidents due to local media coverage.

HPUs have difficulty in collecting information on the existence of any patients with delayed symptoms following an acute incident. The recording systems of hospitals do not enable such information to be easily acquired.

What is already known on this topic?
The toxicological effects of acute exposure to chlorine are widely documented. Chlorine is extensively used in the chemical, manufacturing and water treatment industries. Swimming pools are the largest single location of acute chemical incidents involving chlorine reported to both the Health and Safety Executive and the HPA. Isolated published reports of acute chemical incidents associated with swimming pools have described situations in which a large number of people are exposed and/or high levels of chlorine inhalation occurred.9–17 There is only one previously published report on a series of chlorine incidents in swimming pools, which just presents information on the number and severity of patients associated with each incident.18

What this study adds
This is the first published study that systematically reports on the causes, population exposure and public health management of all acute chemical incidents associated with swimming pools over a given time period. This study has demonstrated that such incidents are relatively common and can lead to the evacuation of a large number of people and cause significant anxiety and media coverage. However, in contrast to the isolated events previously published, in the majority of incidents that occurred during the study period, the chemical release was confined to a plant room. Although large numbers of people were evacuated, very few, if any, people were exposed and no one exhibited severe health effects.

The majority of incidents occurred during the study period were caused by leaking chemical pipes/tanks or by human error leading to inadvertent mixing of chemicals. This suggests that preventative strategies should be directed at improving plant room maintenance procedures and staff training and supervision. In addition, the fact that the majority of incidents were confined to the swimming pool plant room suggests that incident management procedures should ensure that plant rooms are rapidly secured following a chemical leak/release to limit exposure.

In many of the incidents evacuation of the pool and dispersal of those involved occurred before the arrival of the emergency services. In several cases, this occurred even when the chemical leak was confined to the pool plant room. Evacuation of wet, poorly clad swimmers into the external environment may have other health consequences. Hypothermia is a recognized risk when wet decontamination is used following a chemical incident, and children are particularly susceptible.23 In addition, early dispersal from the site may result in exposed persons not receiving appropriate advice and/or treatment.

To address these issues, we suggest that swimming pool regulators (Health and Safety Executive or Local Authority24) work with pool operatives to develop clear incident management protocols to prepare for such incidents, with appropriate advice from health protection colleagues. Such protocols should include consideration of when full pool evacuation is justified and mechanisms to ensure that advice on the consequences of chlorine exposure and the need to seek medical care if delayed symptoms develop is available at the pool to provide to affected individuals. In addition, as set out in the HPA Acute Chemical Incidents—Basic Checklist,25 health protection services should contact Primary Care Trusts when an incident occurs so that local general practices and emergency departments can be warned of the possibility of people self-presenting for clinical care.

Limitations of this study
This study included only incidents reported to the HPA or reported in the local or national media. It is possible that some smaller incidents that did not result in the involvement of the emergency services or media interest may have been overlooked.

This study was limited to a 5-month summer period (June–October 2007). However, this study period was chosen to correspond to the season in which the majority of chemical incidents associated with swimming pools (over 70%) have occurred in previous years.

The information collected about the incidents was obtained from local HPU, emergency services and local authorities, and was sometimes incomplete. For one incident, it was not possible to obtain information about whether the person exposed had any symptoms, and for two incidents there was no information about whether the causalities who had attended hospital required in-patient admission. There was very little information available about whether anyone was admitted to hospital with delayed symptoms due to post-acute respiratory syndrome following these incidents. This highlights the difficulties HPU have in accessing clinical information about individual patients admitted to hospital after chemical incidents.


   Acknowledgements
TOP
 Introduction
 Methods
 Results
 Discussion
 Acknowledgements
References
 
We would like to thank all the members of the emergency services, local authorities and Health Protection Units who provided information for this study.


   References
TOP
 Introduction
 Methods
 Results
 Discussion
 Acknowledgements
 References
 

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