1. Introduction
The Czech government and authorities consider security problems to be crucial issues of interior policy. Chemical terrorism and protection against it have been thoroughly focused on by the Czech government and authorities. Means of public transport and especially the Prague subway represent sites potentially threatened by a terrorist attack.

There is just one subway in the Czech Republic. It is located in Prague, its capital. The Prague subway serves three lines. Recently, several state funded projects have dealt with a possible chemical attack in the underground. Nevertheless, their results have not been published because outcomes of such studies are rarely made public; they are usually subjected to concealment because the survey conclusions might easily be misused by terrorists to implement a chemical attack in the subway.

2. National directives
Legislation has been regarded a priority by the Czech politicians. This chapter illustrates their awareness of necessity to be prepared for possible threats.
The Chemical Weapons Convention, an international agreement (Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on their Destruction), was being prepared by the United Nations bodies for more than 20 years. In January 1993, the treaty was signed in Paris and it entered into force as late as on April 29, 1997, four years later. At that time, Hungary, the 65th signatory, sent their instruments of ratification to Paris. In 1997, the Czech Republic had already prepared its own national Act No. 19/1997 Coll. on chemical weapons prohibition and also its executive decree that was later subjected to essential modifications and released as a new regulation in 2008.
The unique approach of the Czech authorities is reflected in authorization of the State Office for Nuclear Safety in Prague with solving problems of ban on chemical weapons. Details on activities and orientation of the office can be found elsewhere(1); further information is provided in the chapter on Chemical weapons prohibition.

Besides, the directive Strategy of the Czech Republic in the fight against terrorism has periodically been issued since 2002. At first, this nation-wide regulation was made public annually, followed by a biannual release at a later stage.

3. The threat of chemical terrorism in the subway
The vulnerability of undergrounds to chemical terrorist acts was firstly proved in the 1995 Tokyo subway sarin attack. Even if many common chemical warfare and also toxic industrial compounds can be misused, major attention is justifiably paid to possible use of nerve agents like sarin, cyclosarin, soman, and tabun.

Unfortunately, quite many toxic industrial compounds with suitable physico-chemical properties and high toxicity can also be misused in terrorist attacks in undergrounds. The list of easy-to-misuse substances comprises compounds such as phosgene, phosphane, chlorine, hydrogen chloride, hydrogen sulphide, or less, but deadly toxic chemicals like ammonia, sulphur dioxide, and carbon disulphide. Huge amounts of toxic industrial compounds are stored in plants and transported throughout the Czech Republic. They can be stolen and easily used by terrorists to implement chemical attacks.

Possible scenarios of an act of chemical terrorism in the underground have been elaborated to install preventive, repressive, protective, liquidation, rescue, and recovery measures; nevertheless, modelling propagation of hazardous chemical toxic substances in underground with its specific air flow is very difficult. In the Czech Republic, tests and experimental measurements of contaminant proliferation were implemented by using safe simulation substances. The use of air conditioning system supports the propagation of a distributed toxic substance(2). The results of the experiments have not been made public.

4. New emergency plan Response to a chemical attack in the underground
In July 2013, a completely new type of a response plan to a chemical terrorism act was put into operation in the Czech Republic. This 108-page emergency managerial plan of response to an attack in the underground has not been published since it is subjected to concealment. The directive was compiled after implementation of many simulation experiments with proliferation of contaminants in the underground. Implementation of the above model tests is regarded unique within Europe(3). Strong air flow showing special effects like so called piston effect, that is pushing air by train movement in the tunnel, use of ventilation system and shafts are considered the crucial factors in proliferation of contaminants in the subway.

The above new directive in response to a chemical attack in the underground provides detailed information on a possible act of chemical terrorism in the Prague subway and on recovery of its operation. It specifies response activities of individual components of the Integrated Rescue System (IRS) such as the Fire Rescue Service, Medical Rescue Service, Czech Police and other bodies. The emergency plan also gives details on their mutual collaboration in rescue operations and other instructions for a successful intervention after a chemical attack including delivery of information to underground passengers and to people outside the subway(3). The emergency response plan can save hundreds to thousands lives and protect health of possible victims of a terrorist attack in the subway. Brief information on the above emergency instructions was published in the Czech journal called 112 that focuses on fire protection, IRS and population protection(4).

The conception, content and extent of the emergency response plan make it a unique methodical material intended for the IRS bodies. A chemical attack in the underground is not supposed to affect only the subway, but also life in the Czech capital. The collapse of the Prague transport system is expected thanks to the fact that three subway lines form its linchpin.

Many authorities and bodies such as the Ministries of Interior, Health and Defence, the State Office for Nuclear Safety and other institutions participated in preparation of the emergency response directive4. Firstly, a basic concept of passenger rescue, decontamination and first aid was elaborated by the Fire Rescue and First-Aid Services and then it was completed based on discussions with experts from the Police, Czech Army, and Prague Municipal Government and with forensic medicine specialists; results of experiments and tests with simulated propagation of suitable chemical substances in the Prague subway were also considered3. Naturally, the emergency directive is built on theoretical background, thorough safety study and literature search.

The Czech public was briefly informed about the new emergency instructions in specialized Czech journals and conference proceedings by experts like Zdenek Hanuska and Petr Kysilko. Sketchy information was provided so as to prevent its misuse.

5. Conclusion
Many practical tests implemented in the Prague underground showed how to protect passengers against threat and effects of chemical terrorism. Passenger lifesaving, protection of their health and safe transport represent permanent priorities of the Prague Public Transit Company. Prague subway passengers are to be informed about the threat of a possible chemical attack in a suitable way. They will also be shown simple and effective protection against a possible chemical attack.

Travelling comfort of the underground passengers will be enhanced by their awareness of the new thorough emergency response plan that organizes all the essential activities after a possible attack and also by their consciousness of outstanding preparedness of rescue bodies.

This article has been co-authored by Dr. Lenka Fiserova, who specializes in the problems of chemical terrorism and in mitigation of terrorism threats.

Acknowledgement
The authors gratefully acknowledge the assistance received from the Czech Ministry of Education, Youth and Sport within the project Problemy bezpecnosti 21. stoleti a ochrana obyvatelstva (Safety threats in 21st century and population protection) (CZ.1.07/2.2.00/28.0068).

Notes
1https://www.sujb.cz/en/

2Navratilova, L. Protection of population in case of leak of a toxic agent in public building. The Science for Population Protection 2013, 4, 23-34

3Hanuska, Z. Typova cinnost “Reakce na chemicky utok v metru” (In English: Emergency plan: Response to a chemical attack in the subway), in Sbornik prednasek, proceedings of the MEKA conference, Brno, Czech Republic, 2014, available at http://www.meka-brno.cz/sbornik_2014/default.htm on May 20, 2014

4Neklapilova, V. Siroke spektrum projednavanych temat (In English: Wide spectrum of discussed topics), 112 2014, 4, 14-15