Multifunctional device for explosion detection [631713]

Multifunctional device for explosion detection
Davit Khomeriki1*, Nikoloz Chikhradze1 , Edgar Mataradze1, Mikheil Chikhradze1,
Karlo Tavlalashvili1 and Shalva Marjanishvili2
1G.Tsulukidze Mining Institute, 8 E. Mindeli str., Tbilisi, Georgia
2Hinman Consulting Engineers, inc., 601 California St Suite 1710, San Francisco, CA, USA
Abstract. A strategy for physical protection of critical infrastructure
implies the creation of a detective system enabling quick and accurate
identification of the accidenta l and terrorist explosion/fire location and
subsequent transmission of distress signal to the rescue service. Proposed
wireless system for the identification of unauthorized explosions and
activation of protective device in underground facilities consists of
transmitter and receiver modules. A transmitter module contains a sensor
and a microprocessor equipped with blast/fire identification software. A
receiver module produces an activation signal for the operation of an
absorber. The testing has yielded the following results: the time span
between the moment of receiving a signal by the sensor and the moment of
activation of a start signal is 2.4 millisecond; the distance between a
transmitter and a receiver in a direct tunnel – at least 150 m; in a tunnel
with a 900 bending – 50 m.
1 Introduction
Despite the strict regulations for the prevention of explosions and fires in tunnels and
antiterrorist actions, the statistics of accidents and their consequences is extremely grave. It
would be sufficient to m ention terrorist blasts in London (52 people killed and 200 injured),
Madrid (52 people killed and 1800 injured), Paris (8 people killed and 700 injured), Tokio,
South Korea, Moscow and Baku undergrounds. In the case of the fire in the Eurotunnel in
2008, it took 75 minutes for the fire services to respond. Furthermore, throughout this time,
the active ventilation system in the tunnel contributed to the strength of the fire
(<http://en.wikipedia.org/wiki/2008_Channel_Tunnel_fire>). On April 17, 2013 The
devastating explosion at a West Texas fertilizer storage facility killing 15 people, injuring
more than 200 and leveling surrounding homes and businesses in a four -block radius
exposes a chilling trend in the way chemical safety is managed
(www.prweb.com/rel eases/2013/5/prweb10737885.htm). According to statistical data,
several hundred human die each year due to the methane explosion in coal mines. Methane
explosion in one of the mines in Russia, caused by malfunction of the detection system,
took the lives o f 50 people ( http://news.rambler.ru/6289910/?page=2 ).
Hence, the time of response and the reliability of currently deployed detection systems
are failing to meet their requirements and accordingly thei r functions remain limited.

* Corresponding author: davitkh [anonimizat]

Reliable protection from accidental and terrorist explosions requires quick and accurate
identification of the explosion/fire location and transmission of information to ensure the
immediate operation of protection systems and s witch the emergency mode. Considering
the growing threat of terrorist or accidental explosions in tunnels and other underground
infrastructure, it appears urgent to be improved the systems for detecting the threats in order
to protect people from explosion s in underground facilities.
2 Methodolical Issues of Detection System
The development of contemporary detection systems is oriented to the creation of
integrated systems ensuring monitoring of all possible threats that may endanger facilities
to be prote cted as well as respective measures for threat prevention. A comprehensive
security system will enable identification of emergency and pre -emergency conditions and
have WiFi modes of operation. The system will be quick -acting and reliable and not
impede th e normal functioning of the underground facility. In order to achieve realibility,
the system must not depend on the external power. It must have a of possibility controlling
in a test mode. Detection system shall meet the requirements of the Directive 94/ 9/EC on
equipment and protective systems intended for use in potentially explosive atmospheres
(ATEX).
Together with threat monitoring and transmission of information, detective systems
designed for underground structures and manufacturing sites with hazar dous conditions
serve to generate a signal for the activation of explosion suppression equipment, switch the
ventilation system into an emergency operation mode as well as regulation of explosion
protection vents, explosion resisting doors, protection pan els or other automatic protection
facilities [1,2,3]. In general, a structure of an integrated detection system consists of i)
threat identification and emergency signal generation module; ii) emergency signal
transmission module and iii)emergency signal r eception module.
System design process requires the following stages:
• Risk analysis of the facility to be protected; definition of the function of the system;
• Determination of emergency and pre -emergency identification parameters and definition
of res pective limiting values;
• Selection of sensors;
• Development of identification module and electric scheme of emergency signal
generation;
• Selection of a wireless technology of data transmission and determination of working
frequency ensuring signal tra nsmission at a required distance;
• Selection of main technical properties of signal transmission and reception modules and
development of their electric scheme;
• Selection of a power supply source for the system;
• System testing, adjustment and determin ation of its reliability.
3 Wireless System for the Detection of Threat and Activation of
Protective Device
3.1. Structure of system
G.Tsulukidze Mining Institute, CIPPS and Hinman Consulting Engineers, inc. has designed
Wireless system for detection acci dental explosions and fire in underground structure and
coal mines, where the risk and probability of explosion of methane and carbon dust.
The system contains the following elements:

• a module of sensors for the identification of explosions, fires, smok e and methane;
• a module for the identification and generation of an emergency signal;
• an emergency signal transmission module;
• an emergency signal receiving module ;
• a power supply module.
The system design is based on the following principle: it pr ovides constant monitoring
of explosion and fire identification parameters. With the reaching of the values of these
parameters the ceiling values, the module will generate a high -frequency electric signal
which will be transmitted to the receiving module.
The identification criteria and limiting values for generation of alarm signal is given in
Table 1.
Table 1. The identification criteria and limiting values for generation of alarm signal
Threat The identification
criteria Limiting value Sensor

Explosi on

Emergency
conditions Overpressure 12 kPa Pressure sensor
Pre-emergency
conditions Concentrations
methane in air 2% CH4 sensor
Fire Emergency
conditions Flame The area of the
site of the fire
exceeds 0,5m2 IR flame
sensor
Pre-emergency
conditions Smoke The percent of
obscuration per
unit length
exceeds 5%/m Smoke sensor

On the base of identification criteria the softwere was created for the functioning of
identification module (signal transmtter ). The relevant algorithm enables to generate and
process the identified emergency signals for further security actions.
3.2 Wireless technology of data transmission
The data transmitting system consists of: fast receiver, the data coding and decoding knots
and amplitude (peak) radio transceiver. For cod ing and decoding of data microprocessors of
AVR type are used, which work at 18MHz clock frequency. The duration of data signal is
0,8ms. In order to increase the reliability the data signal is transmitted 3 times and the
emergency signal is generated afte r receiving all 3 data signals. The data transfer rate is
30kB/s. The receiver of the system is responsible for the fast processing of the information
in order to generate relevant information for the information board, security service or
external automo tive protective device. The main parameters of the system are given in
Table 2.
Both, the transmitter and receiver modules have two operation modes: on -line and test.
In the on -line mode of operation, both, the transmitter and the receiver are prepared to react
to the blast. The test mode of operation serves to control the working capacity/ability for
the transmitter and receiver blocks.

Table 2. Main parameters of the system
Parameters Transmitter Receiver
Independent source voltage, V 9 12,6
Supply current, mA Min 4; Max 200 10
Operating frequency, MHz 433,92 433,92
Data transfer rate, kB/s 30 30
Data Encoding ASK ASK
Output power of transmitter,
dBm + 30 –
Rreceiver sensitivity, dBm – -115 dBm
4 Results of the Wireless System Testing
Preliminary tests and tests at real explosions of system are conducted. Results of
preliminary tests have shown working ability of the system. The reliable signal
transmission and signal receiving is observed when distance between tra nsmitter and
receiver modules in a direct tunnel was at least 150 m, in a tunnel with a 900 bending –
50 m. Besides, no false or ignorance of signals was observed.
Testing methodology at real explosions envisages the inspection of working capacity of
all the components of the system (detection and signal generation module, transmission and
receiving wireless device, control block of absorber) as well as the determining of time
parameters of the system. Blasts experiments were organised in a special chamb er. The test
bench had a rectangular cross -section and was made of steel sheets. The dimensions of the
bench was: length – 3 m, width – 0,4 m and height – 0,6 m (Fig . 1).

Fig. 1. System testing circuit
During the experiments the following four time char acteristics are measured:
– Moment of Blast;
– Moment of shock wave arrival to sensor;
– Moment of signal arrival to receiving module, which is places in absorber control block;
– Moment of absorber activation.
Two pressure sensors were installed in the test bench at the distance of 2,5 m from the
place of blast. One sensor was connected to the detector, while another to an oscilloscope,

which recorded of shock wave arrival to sensor. A radio signal generated in a detector was
transmitted to receiving mo dule, which is placed in absorber control block. The distance
between the detector and the receiving module was 30 m. The control block gives start
signal to an electrical initiator of the gas generator. A pressure sensor was installed in an
absorber hydro cylinder and connected to an oscilloscope to record peak pressures
generated in a hydro -system under the impact of high pressure after the activation of a gas
generator. The time histories of signal generation, transmission and receiving are presented
on Figure 2.

Fig.2 . The time histories of signal generation, transmission and receiving
The test results showed that the time from blast moment to the moment when the shock
wave reaches the blast sensor is 4 ms, which is relevant to the shock wave velocity of
625 m/s at 2.5 m distance. Besides, 2.4 ms is necessary between the sensor activation and
generation of emergency signal. The total time which is recorded from blast moment to the
absorber activation, is 11ms.
5 Conclusions
Experience shows that devices used to protect from unauthorized explosions in
underground facilities, fail to meet modern requirements. The development of effective
automated protective facilities requires the improvement of the reliability and response
speed of its base component, i.e. the system for blast detection and activation of a
protective device.
The preliminary investigations are carried out and have designed wireless system for
detection accidental explosions and fire in manufacturing sites and coal mines, whe re the
risk and probability of explosion of methane. The system provides the following 2
activities:
a) Sending the information to the security service. This information includes: Emergency
level (emergency or pre -emergency conditions), type of threat (ex plosion or fire), place and
time of the threat/accident;
b) Activation of automatic protective device.
Results of tests of system show that potentially, it can be used for identification of
danger in 2.4 ms after excitation of a sensor of the detector and activation of protection
device in 11 ms after the blast moment.

6 Acknowledgements
This research is sponsored by SRNSF and NATO in the framework of “Science for Peace
and Security Programme”.
References
1. S. Podobrazhin, A. Dzhigrin, A. Gorlov , Explosion protection of coal mines. Fire automatics,
2007 (in Russian).
2. R. Zalosh, New Developments in Explosion Protection Technology. Fire and Emergency
Services , Asia, Singapore (2005 ).
www.firexplo.com/images/New_Explosion_Protection_Technology.pdf
3. N. Bochorishvili , N. Chikhradze, E. Mataradze , I. Akhvlediani , M. Chikhradze,
T. Krauthammer , New Suppression System of Methane Explosion in Coal Mines. Procardia
Earth and Planetary Science , 15, 720-724 (2015).