«TM VESDA ECO by Xtralis White Paper Aspirating Smoke Detection (ASD) with Gas Detection and Environmental Monitoring A Reliable and Cost-effective ...»
VESDA ECO by Xtralis
Aspirating Smoke Detection
(ASD) with Gas Detection and
A Reliable and Cost-effective
This white paper introduces a novel technology that combines aspirating
smoke detection (ASD) with sensors for the detection and monitoring of
gases and other environmental hazards. This unique combination delivers
increased value over individual ASD or conventional gas detection
systems, including full integration with fire alarm control panels (FACPs), heating ventilation and air conditioning (HVAC) systems, programmable logic controllers (PLCs), and building management systems (BMS) and delivers a lower total cost of ownership compared to conventional smoke and gas detection and monitoring technologies.
This paper features three case studies, starting with a battery-charging room, where it is important to monitor for smoke, as well as hydrogen gas, to ensure life safety and avoid a catastrophic explosion or another fire/gasbased disaster. The final two case studies cover car parking facilities and tunnels, both having unique requirements for safety and ventilation monitoring that can be answered with the use of aspirating systems.
VESDA ECO by Xtralis White Paper — ASD with Gas Detection and Environmental Monitoring Background For many years, ASD systems have offered highly sensitive, very early warning smoke detection. Such systems, like VESDA by Xtralis, exhibit installation flexibility with the capacity to be easily modified in response to changing operations within the protected area. While delivering high sensitivity, VESDA also has programmable alarm thresholds that allow for the management of various fire conditions – from a simple alert to the automated call out of fire services or instigating suppression release.
The cumulative effect, where smoke enters more than one ASD sampling hole simultaneously, is particularly useful in high-airflow environments or areas where high levels of smoke dilution is anticipated. Large, open spaces such as warehouses, cold-storage facilities, manufacturing environments, and cable tunnels all benefit from the unique deployment of a VESDA ASD system. ASD devices can, therefore, provide reliable very early warning fire detection in situations that would present a challenge to conventional detection methods. VESDA detectors installed worldwide protect up to 3 billion square feet (300 million square meters) in various environments.
With such an infrastructure in place, it is a small step to increase the scope of the ASD to provide multi-substance detection beyond smoke. Many of the environments protected by a VESDA system are workplaces where codes, legislation, regulations or good working practices dictate that the employer will provide all employees with safe, healthy and comfortable conditions, the most important being ambient air. Breathing air needs to contain the correct concentration of oxygen (20.9% vol) and be free of unwanted gases or vapors.
Other monitored environments need to provide protection against airborne contaminants, especially car parks, garages and road tunnels, where the combination of carbon monoxide (CO), nitric oxide (NO) and nitrogen dioxide (NO2) can be deadly. Shopping malls built on reclaimed land may exhibit a risk of naturally occurring gas seepage, perhaps from old mining operations or the decay of trash in underground landfill sites, particularly methane (CH4) and carbon dioxide (CO2).
Conventional gas detection systems, which are comprised of a network of remotely mounted diffusion gas sensors,
often can be expensive or unsuitable, especially in certain situations:
Where accessibility of cabled detectors for calibration/maintenance is problematic Areas of heavy vibration/shock/impact Where there is no possibility of remote cabling or no remote-alarm requirement Hazardous locations where it is preferable to avoid electrical connections at the potential leak site Low-level fuel spillage – vapor collection at various heights just above liquid level, e.g., bund monitoring Where the air sample needs conditioning (cleaning, drying, heating or cooling) before it can be passed to the gassensing transducer Where vandalism of remote electrical apparatuses is likely General applications where wide-area coverage is required When they are not integrated into other safety equipment or third-party systems Application Areas Gas detection is a mature science, but the majority of these systems use the conventional topology of cabled, remote detectors with power supplies and data communications wired to central controllers and power units. In many applications, such topology is impractical, and using an ASD for combined smoke and gas monitoring delivers both
cost and reliability advantages for:
Transportation centers – car parks, road tunnels, vehicle maintenance workshops Battery-charging rooms – hydrogen risk Utility and cable tunnels Inerting spaces – reduced oxygen monitoring
Technique A VESDA system typically uses a network of sampling pipes through which representative air samples from within an indoor environment are drawn by a remotely mounted pump, which is situated in a cabinet that also contains the smoke-detection apparatus. If the air needs to to be sampled for the presence of unwanted gases or fumes, the VESDA ASD system can be converted quite simply into a VESDA ECO system by the installation of one or more ECO gas detectors, which are inserted into the pipe network as illustrated below.
Air is actively drawn into the sampling pipes for early detection of smoke and gases in one cost-effective, integrated solution.
Each detection point can be fitted with one or two gas sensors. A small portion of the sampled air is directed into a cavity containing the sensors before being returned to the pipe. The detector design is such that its insertion into the pipe network has a negligible effect on smoke transport time. The cavity has a separate, sealed port for testing and calibration purposes, as periodic checking of the gas sensors may be a requirement of workplace codes or regulations.
Digital Technology Each VESDA ECO detector has built-in intelligence and signal-processing capabilities with 2GB of memory for recording events and values locally. Digital transmission of data by Modbus/RS 485 to a central controller enables a single VESDA ECO Controller to support up to 128 detectors with the potential for up to 256 separate gas sensors. The controller can calculate time-weighted averages of gas presence, which is an essential calculation when considering workplace exposures to toxic gas. Alarm or action trigger points can be set, and these also can include setting unique hysteresis bands that enable an alarm relay to be energized at one gas concentration and de-energized at a lower concentration, simplifying demand-controlled-ventilation applications.
Environmental Control and Energy Savings A VESDA ECO system can provide detailed information about the environment being monitored. With knowledge of the ambient conditions, intelligent and automatic decisions can be made about air quality. Digital communications between the VESDA ECO and existing PLC/HVAC/BMS can enable appropriate levels of ventilation to be applied to road tunnels or car parks, dramatically reducing electrical energy consumption when compared with fans that are powered permanently.
System and Network Topology To achieve great savings in cabling and installation costs, mounting a VESDA ECO detector close to the VESDA smoke detector’s inlet manifold may be preferred. However, if the gas characteristics do not allow this, then localized mounting closer to the sampling point may be more appropriate. Or mounting the gas detector on the exhaust port of the VESDA smoke detector could allow a single VESDA ECO installation to monitor gas concentrations coming from any of the multiple zone inputs, providing total-area coverage. Xtralis has significant experience in the deployment of ASD sampling points and can provide expert assistance in gaining as many advantages from the system topology as
possible. These include:
Reducing cabling costs and complexity Allowing maintenance to be carried out away from the monitored site Sampling from hazardous, dirty, harsh or otherwise inconvenient locations Detering vandalism through “invisible” sensing points and to suit site aesthetics
Gas Suitability Only a few simple points need to be considered in assessing the benefits and suitability of a VESDA ASD and pipe network. For example, the distributed coverage of the site by multiple sampling points could lead to dilution of the measured gas concentration. Flow-failure monitoring can be established for high reliability or on long pipe runs, but some species of gas are more suitable for the aspiration technique than others as shown in the following table.
Case Study 1: Battery-charging Rooms Background Electrical energy storage is now a major consideration in many industries, ranging from the need to supply permanent power to computer rooms via an uninterruptible power supply (UPS) to large-scale power generation and storage from renewable resources such as wind energy. Also taking into account the growth in the use of electric or hybrid vehicles and the need to charge traction batteries en-masse (including military applications such as submarines), it is easy to imagine the number of battery-charging rooms that now exist in factories and office buildings.
Rechargeable batteries all use an electrochemical reaction to convert available electrical current into stored chemical energy. This chemical reaction can produce quantities of hydrogen gas (sometimes known as off-gassing), which is highly flammable and has led to some catastrophic explosions when not managed properly. Key to the safety of battery-charging room installations is the ventilation of the air spaces above the batteries (hydrogen is approximately fourteen (14) times lighter than air, so it rapidly rises away from the source of its generation), but permanent ventilation can be inefficient and costly if it is left running when no hydrogen is being created.
The electrochemical reaction that occurs when charging batteries can be more efficient if the ambient temperature is maintained within suitable limits, so it is commonplace to see an air-conditioning apparatus installed in the room.
The large electrical currents flowing into or from the batteries can spike to high levels when a current disturbance occurs, or other heavy load on the batteries is applied, so there is a real risk of heated cables, smoldering insulation, melted plastic fittings and cable fires. Therefore, very early smoke detection is an essential part of the safety infrastructure for a battery-charging room.
Solution A VESDA ECO system combines fire protection and gas-monitoring capabilities in one system. The ASD system delivers the well-known benefits of very early warning fire protection, and the VESDA ECO detector provides the ability to detect flammable hydrogen gas. This unique dual-monitoring concept significantly reduces costs over the installation of separate conventional protection systems, including cabled-smoke detectors and cabled-gas detection. VESDA
ECO also can combine the inputs from its various sensors to subsequently control:
Variable-speed fans, allowing demand-controlled ventilation Early-stage smoke detection, fire alarms and extinguishing systems Gas detection and inputs to FLCP, HVAC and BMS Gas alarms to meet local regulations
Battery room — monitor hydrogen level for explosion protection and demand-controlled ventilation Case Study 2: Car Parks and Garages Background The regulations and recommendations for monitoring air quality within car parks or vehicle garages vary tremendously across the globe. However, ventilation should be installed and used whenever there is a build-up of harmful gases or fumes from vehicle exhausts within the local environment. But which gases should be monitored, how many detectors should be installed, and what are the concentrations that constitute an increase in ventilation or an evacuation?
A review of global guidance shows a lack of consistency. For example, some countries state that carbon monoxide monitoring is sufficient, while others add nitrogen oxides (NO, NO2), as well as the need to monitor for flammable vapors that could indicate fuel spills. If the vehicle engines within these confined spaces primarily use gasoline (petrol) with catalyzed exhaust systems, it is likely that an increase in carbon dioxide, as well as carbon monoxide, will be prevalent. However, if diesel engines dominate, the build-up of NO and NO2 may need to trigger an action. And if recharging points for electric vehicles are nearby, an argument for hydrogen monitoring can be made, as covered in Case Study on previous page. But in theory, maximum protection against gas risks from all vehicle types might require the installation of detectors for all six gases at every monitoring point, which is a cost-prohibitive requirement.
Guidance on the number of detectors and their spacing also is inconsistent. Some regulations state that all parts of the car park should not be more than 25 meters (83 feet) from a gas detection point, while others suggest that placement should be based on a calculation of the number of detectors for a given area – i.e., one detector per 200 square meters (2,178 square feet) or one detector per 400 square meters (4,356 square feet) in some European countries.
Solution To provide adequate gas detection coverage in large car parks or garages using conventionally cabled detectors is likely to be very costly and complex, especially if all of the apparatuses need to be vandal-proof.