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01/09/2005 European Safety @ Work council annual meeting


Shipyard industry consists an occupational environment of high risk, where severe accidents have occurred including fatalities and cases with days away from work, job transfer or restriction. While existing legislation regarding health and safety issues has been recently expanded, its implementation is problematic, mostly due to lack of technical expertise and insufficient official supervision.




Abstract

Shipyard industry consists an occupational environment of high risk, where severe accidents have occurred including fatalities and cases with days away from work, job transfer or restriction. While existing legislation regarding health and safety issues has been recently expanded, its implementation is problematic, mostly due to lack of technical expertise and insufficient official supervision. The objective of the present project was the development of a wireless on line Gas Monitoring System (GMS) for the measurement of flammable gases in ship tanks, in order to prevent relative accidents. The system built includes a wireless network of two Remote Measurement Terminals (RMTs) and one Remote Host Terminal (RHT). The RMTs are equipped with properly selected Infrared (IR) gas detectors. The RHT collects, registers and processes the data obtained by RMTs from remotely located measurement sites. The RHT can also display the results graphically, in real time, and produce audio messages. The System’s energy demands are covered by a battery, rechargeable through a photovoltaic system.

The System was tested through concurrent measurements of GMS and well-calibrated portable gas detectors inside ship tanks. The results were highly comparable (deviation 1% LEL), although there was a small lag of GMS response, in highly altered concentrations, especially in small vessels; this is mainly because IR sensor is based on diffusion, while portable instruments use suction pump. For larger vessels, however, response times were similar for both detectors.

The proposed GMS can prevent exposure from harmful burnout events and has the possibility to drastically decrease fatalities and injuries. Only in free ship repair zone in Perama, 12 workers died in six accidents since 1998. Under a cost-effective approximation, the prevention of only one severe injury excuses the implementation of GMS in a workplace. Therefore this System may prove extremely useful when planning the safety strategy for hazardous occupational environments where flammable gases are present.

Introduction

The twentieth century witnessed remarkable reductions in the number and rate of occupational fatalities and injuries. However, many preventable injuries and deaths still occur. More than 300 major chemical accidents have been registered in the European Chemical Accident Center during 1985 – 1997. A large part of these accidents were caused by release of flammable gases and liquids, particularly vapor cloud explosions (Abbaspour, 2005).
Recently, many research and development activities have been conducted world wide for the purpose of putting together computerized systems for risk assessment and emergency planning (Alhajraf, 2005). Shipyard industry consists a characteristic example of an occupational environment of high risk, where severe accidents have occurred including fatalities and cases with days away from work, job transfer or restriction. While existing legislation regarding health and safety issues has been recently expanded, its implementation is problematic, mostly due to lack of technical expertise and insufficient official supervision.
The objective of the present project was the development of a wireless on line Gas Monitoring System (GMS) for the measurement of flammable gases in ship tanks, in order to prevent relative accidents. This system provides the possibility of constant control and recording of the flammable gases concentration inside an occupational environment, with the ultimate goal to prevent occupational accidents that have in the past occurred due to explosions during repair works.

Methodology

The design of an on-line gas monitoring system combines a number of different technologies, such as:

Gas detection
Data transfer
Presentation and utilization of the data collected
Autonomous energy supply

The system built includes a wireless network of two Remote Measurement Terminals (RMTs) and one Remote

Host Terminal (RHT).

GMS Components

1. Remote Measurement Terminals (RMTs)
The RMTs are equipped with the gas detectors as well as with process / transmission units.

1.1. Gas detector
Two different detection methods were proposed:

Direct detection, where the detectors are placed inside the under study tank and indirect sampling, where a flexible tube is dipped into the tank. Gas samples are drawn with the use of a pump and are then lead to the detector, which is placed onto the vessel’s deck
Indirect sampling was found to be problematic since the response time could exceed 60 sec, depending on the length of the sampling tube. In addition, the moving parts of the pump have larger maintenance and energy needs.
Therefore, direct detection was chosen.
Between Infra Red (IR) and Pellistor detectors, an IR detector was preferred since IR detectors are not influenced by substances that may poison the Pellistor catalysts. Moreover, IR detectors have a larger lifetime and easier maintenance.

According to the Greek Legislation, the designated limit concentration, for Petroleum products into a tank, is equal to 4% of the LEL (Lower Explosion Limit). In the case of hot works this limit is equal to 1% of the LEL. Thus, a sensor with a range of 1-20% of the LEL was selected.

1.2. Process / Transmission Unit

The Process / Transmission Unit consists of:
A processing module that receives the data collected from the gas detector and transforms them to an appropriate digital form so that they may be managed and transmitted.
A build-in radio frequency (RF) module that transmits the data and
An energy supply system, which includes a battery, rechargeable through a photovoltaic system.

2. Remote Host Terminal (RHT)

The RHT collects, registers and processes the data obtained by RMTs from remotely located measurement sites.

2.1. Central Collection / Process Unit

The Central Collection / Process Unit includes:

- An energy supply system
- An RF receptor module
- A central processor unit that is responsible for the linking of the receptor with the Computer.

2.2. Computer

Through a specially designed software, the Computer displays the results from the measurement of flammable gases graphically and in real-time. It may also produce audio and graphic messages whenever there is an alarm.

Results and Discussion

The System was tested through concurrent measurements of GMS and well-calibrated portable gas detectors inside ship tanks. The results were highly comparable (deviation 1% LEL), although there was a small time lag of GMS response, in highly altered concentrations, especially in small vessels; this is mainly because IR sensor is based on diffusion, while portable instruments use suction pump. For larger vessels, however, response times were similar for both detectors. The System’s development and application tests have brought out new possibilities for further development and interesting fields of application, such as:

The alarms may be sent, through SMS, to the mobile phones of the responsible security personnel.
Depending on the emergency of the situation, the alarms may be also sent to an administration center inside the Shipyard or to other centers, such as the Fire Brigade.
Predefined response actions (such as start-up of ventilation fans, shut-down of pumps, valves, etc.) may be initiated when there is an alarm.
Different types of sensors, such as for toxic gases, may be incorporated to the System to cover a broader range of hazard events.
On the other hand, the collected data archives could be an important source of information for risk assessment and management studies. The GMS collects and stores data from all alarms (date, time, location, flammable gases concentration). These data, when combined with periodic control measurements and other parameters (such as temperature and ventilation), may be used to prevent dangerous situations in the future.
Thus, the proposed GMS can prevent exposure from harmful burnout events and has the possibility to drastically decrease fatalities and injuries. Only in free ship repair zone in Perama, 12 workers died in six accidents since 1998. Under a cost-effective approximation, the prevention of only one severe injury excuses the implementation of GMS in a workplace. Therefore this System may prove extremely useful when planning the safety strategy for hazardous occupational environments where flammable and toxic gases are present. It may proove to be an indispensable part of the overall security system design for the Shipyard Industry.

Acknowledgements

This work was funded by the Hellenic Institute of Occupational Health and Safety and the European Fund for

Regional Development.

References

Abbaspour M., Mansouri N., “City Hazardous Gas Monitoring Network”, Journal of Loss Prevention in the Process Industries, Vol. 18, p. 481-487, 2005.
Alhajraf S., Al-Awadhi L., Al-Fadala S., Al-Khubaizi A., Khan A.R., Baby S., “Real-Time Response System for the Prediction of the Atmospheric Transport of Hazardous Material”, Journal of Loss Prevention in the Process Industries, Vol. 18, p. 520-525, 2005.
Haddix A.C., Mallonee S., Waxweiler R., Douglas M.R., “Cost Effectiveness Analysis of a Smoke Alarm Giveaway Program in Oklahoma City, Oklahoma”, Injury Prevention, Vol. 7, p. 276-281, 2001.
Stout N.A., Linn H.I., “Occupational Injury Prevention Research: Progress and Priorities”, Injury Prevention, Vol. 8, p. 9-14, 2002.


 
   

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