Open HSI menu
Subscribe Login

Home / Articles and Press Releases / Article / Safety Hazard Detection

CATEGORIES

  • Latest Issue
  • Above The Neck Protection
  • Chemical Protection
  • Confined Space
  • Construction
  • Emergency Procedures
  • Energy, Oil and Mining Industries
  • Eye Protection
  • Fall Protection
  • Gas Detection
  • Hand Protection
  • Hazardous and Explosive Atmospheres
  • Health and Safety Awareness
  • Hearing Protection
  • Heat and Flame
  • Lighting and ATEX
  • Noise Monitoring
  • Personal Protective Equipment
  • Respiratory Protection
  • Safety Footwear
  • Safety Technology
  • Safety Training
  • Slips, Trips and Falls
  • Wellbeing at Work
  • Working at Height
  • Working Rights

MORE

  • Press Releases
  • Events
  • Videos
  • Webinars
  • Magazines

COMPANY

  • About
  • Advertising
  • Newsletter
  • Contact
Open HSI menu
Subscribe

Home / Articles and Press Releases / Article / Safety Hazard Detection

CATEGORIES

  • Latest Issue
  • Above The Neck Protection
  • Chemical Protection
  • Confined Space
  • Construction
  • Emergency Procedures
  • Energy, Oil and Mining Industries
  • Eye Protection
  • Fall Protection
  • Gas Detection
  • Hand Protection
  • Hazardous and Explosive Atmospheres
  • Health and Safety Awareness
  • Hearing Protection
  • Heat and Flame
  • Lighting and ATEX
  • Noise Monitoring
  • Personal Protective Equipment
  • Respiratory Protection
  • Safety Footwear
  • Safety Technology
  • Safety Training
  • Slips, Trips and Falls
  • Wellbeing at Work
  • Working at Height
  • Working Rights

MORE

  • Press Releases
  • Events
  • Videos
  • Webinars
  • Magazines

COMPANY

  • About
  • Advertising
  • Newsletter
  • Contact

CATEGORIES

  • Article
  • Press Release
  • Above The Neck Protection
  • Chemical Protection
  • Confined Space
  • Construction
  • Emergency Procedures
  • Energy, Oil and Mining Industries
  • Eye Protection
  • Fall Protection
  • Gas Detection
  • Hand Protection
  • Hazardous and Explosive Atmospheres
  • Health and Safety Awareness
  • Hearing Protection
  • Heat and Flame
  • Lighting and ATEX
  • Noise Monitoring
  • Personal Protective Equipment
  • Respiratory Protection
  • Safety Footwear
  • Safety Technology
  • Safety Training
  • Slips, Trips and Falls
  • Wellbeing at Work
  • White Papers
  • Working at Height
  • Working Rights

Article

Safety Hazard Detection

By Ramanathan Somasundaram

| Read Bio

Published: January 01st, 1970

Share this article

This article provides insight into the planning, design, installation, operation and maintenance of fixed gas detectors in the oil and gas industry.

The analysis of past accidents in the oil and gas sector leads us to believe that the loss of primary containment could trigger a major accident, which would pose potential risk to people, assets and the environment – let alone the reputation of the operating company involved.

While oil and gas plants are designed to contain, one should recognise that they are asset intensive and each section has a number of flanges to connect valves, gauges and pumps. In addition to wear, corrosion and human error, these flange joints are the weak links for a potential leak. Any such leak must be detected early to prevent and mitigate the major consequences. The main objective of installing gas detectors is to identify any dangerous conditions, including flammable or explosive atmospheres, oxygen deficient environments and high levels of toxic airborne contaminants.

These environmental conditions translate into the categories of sensors required to detect:

• Flammable gases

• Toxic gases

• Oxygen

In terms of fixtures, gas detectors can be divided into fixed and portable types. As indicated by their name, fixed detectors are permanently installed in a chosen location to provide continuous detection of gas leaks. These detectors provide early warning of leaks, which can then be actioned appropriately to prevent and mitigate the consequences. Portable detectors are small, handheld devices that can be used for testing an environment prior to entry or carrying out a task, for example, testing a confined space for the presence of flammable or toxic gas or vapour before entering.

Plan and design

Gas detector arrangement has to be optimised based on the hazards associated with specific scenarios, as well as to cover the entire facility, reduce the potential for false alarms and enable access during inspection and maintenance. It is important to understand that installing high quality detectors at inappropriate locations may not serve the gas detection objectives. As outlined in the following sections, there are four approaches for planning and designing a gas detector arrangement for any given condition: experience based, prescriptive standards, risk based, and a combination of all the above.

Experience based In this approach a facility relies on the experience of staff and in particular their previous experience of installing gas detectors in similar facilities. This is neither based on any scientific justifications nor on the standards.

Generally a walk through is conducted on the facility to ascertain the gas detector requirements and arrangements. This approach may identify locations, but may overlook the gas accumulation zones and may not fulfil the requirements of the local standards and regulations.

Prescriptive standards In this method the detectors are designed based on standards and regulations. The most widely adopted standards are NFPA 72, fire alarm and signalling code and EN 54, fire detection and fire alarm standards. These standards are encyclopaedic and cover entire aspects including selection, installation and maintenance. Standards also specify requirements for signalling after detection.

• Generally the following factors are specified as guiding principles in locating gas detectors in prescriptive standards:

• Vapour density – below potential leak source for products heavier than air and above potential leak sources for products lighter than air

• Leak pattern and environmental conditions – close to potential leak sources along the predicted leak trajectory

• Location of potential ignition sources

• Impediments

• Access for inspection and maintenance

Due to the innovations, technological changes, evolving compliance requirements and changing market conditions, over time gas detector placement techniques have transformed. Companies have started providing complete and optimal solutions rather than just supplying equipment. These factors drive the oil and gas community towards adopting more scientific approaches. Further to this, it is to be recognised that prescriptive standards have shortcomings, as they are oriented towards occupied buildings and not oil and gas processing facilities.

The oil and gas sector is evolving to meet the changing market conditions. Changes in environmental legislation, for example, led to changes in gasoline and diesel fuel specifications. These changes encourage the oil and gas facilities to use hydrogen for improving the product specification. Further, the ever increasing crude oil prices have compelled processing of heavier crudes, requiring more extensive conversion and product treatment processes, which eventually require more scientific and risk based approaches in gas detection regimes.

Risk based In the risk based approach, a quantitative risk of individual hazards is assessed and risks are quantified to ensure they are as low as is reasonably practicable (ALARP). Use of this technique enables the facility to be more responsive and specific to the gas detection needs. The entire facility is classified into different zones to determine gas detector coverage.

The following factors can be used to determine this zoning:

• The nature of the material handled and its inventory

• Process parameters such as pressure and temperature

• Layout considerations and ventilation patterns such as open area, congested or confined

• Asset protection value

• Occupancy rate

Once the zones are identified, a computer simulation model is used to map the potential gas dispersion in all the zones. A preliminary gas detector arrangement can then be designed by considering the potential gas dispersion and the gas detection targets to be set by the designer. The detection target is driven by the minimum gas cloud size that could result in a significant consequence. Some empirical values can also be used to set detection targets.

A study by the UK’s Health and Safety Executive (HSE), for example, determined that in an offshore platform the energy contained in a six metre propane or methane gas cloud could create damaging pressure waves after ignition. The HSE determined that gas detectors placed at five metre intervals could potentially minimise the damage levels. Readers should also note that toxic gas mapping is more challenging, as there is no general rule for toxic gas cloud size. In this case, concentrations that are considered as immediately dangerous to life or health (IDLH) could be a guiding factor. If the toxic gas concentration can reach levels IDLH, then there is a need to detect its release.

Selection of appropriate performance targets plays a critical role in effective gas detection. The general rule of thumb is the smaller the gas cloud size, the smaller the hazard size and the more effective the gas detection system. Such an approach, however, will require a plethora of detectors all over the facility, which will incur huge cost. This emphasises the need for optimisation, which can be achieved by adopting the ALARP principle. In simple terms, ALARP attempts to strike a balance between cost and benefits.

Based on the above principle, a preliminary gas detector arrangement should be designed. This arrangement must then be verified with the manufacturer’s specifications for suitability and facility visits will be made to check for impediments and access for inspection and maintenance. If it is a facility to be built then this could be verified during the model review process.

Combined approach It is ideal to use both prescriptive and risk based approaches for designing gas detector arrangements. It will be particularly beneficial to use a prescriptive approach for occupied buildings outside the process areas. The location of the gas detector should be determined by analysing the air movement in the building. In an oil and gas facility these approaches compliment each other to formulate an optimal arrangement.

Signalling requirements In determining the signalling requirements, the following factors should be considered:

• Standards and requirements to ensure compliance

• Time required to respond to the signal

• Actions to be taken following the signal

• Toxicity of the gas or vapour

• Any other locality specific factors

It is also necessary to account for ventilation of dead spots where vapours could accumulate, as well as the variability of natural ventilation. To overcome this, it is industry practice to set two levels of signals. One signal, at a lower level, is set as a warning of a potential problem requiring investigation. The higher level signal could trigger an emergency response, such as evacuation or shutdown or both. In general, the lower level signal is set at less than or equal to 10% of the lower explosion limit (LEL) and the higher level signal is set at less than or equal to 25% LEL.

There is a threat that gas detectors are prone to false detection, which can lead to emergency shutdowns. To avoid this a voting system is adopted in the design. Gas detector signalling response should be designed based on the voting system. As an example, a voting configuration of two out of three implies at least two out of the three detectors must detect hazardous gas levels before any signalling system is activated. One limitation of the voting system is that the gas cloud has to grow and be big enough to be detected by multiple detectors before the signalling system will activate.

On the contrary, a false signal in a system indicates that it is partly or completely not functional and in the case of a gas leak the system may not respond as intended.

Management of change Any changes in the materials or process should go through the change management process to ensure the detection and signalling systems are appropriate for the change. If not, measures should be taken to redesign the detector and signalling system.

Gas detection technology

Various gas detection technologies are available in the market place, which can broadly be grouped into:

1. Point gas detection such as catalytic bead sensors or infrared sensors, which work on the gas diffusion principle.

2. Open-path detectors, also called beam detectors, typically consist of a radiation source and a remote detector. The detector measures the average concentration of gas along the path of the beam. The unit of measurement is concentration multiplied by path length, % LEL x m or ppm x m. Systems can be designed with path lengths ranges from 40-140 m.

3. Ultrasonic Gas Leak Detectors (UGLD) have emerged to overcome certain limitations of the above traditional technologies. In traditional gas detection systems the gas has to form a cloud and it should be either in close proximity to detector or within a defined area. UGLD respond by sensing the sound emitted by high pressure gas leaks. The advantages of these detectors are they are not affected by the wind direction or gas diffusion, but they can be affected by background noise within the facility.

Installation

After planning and design the gas detectors have to be procured and installed in the facility. It is important to maintain integrity standards during manufacturing and installation. A well-designed detector arrangement will be effective only if it is installed as planned and designed. Location and orientation of the detectors are the primary factors to be strictly adhered to while installing the detectors. If for any reason the detectors cannot be placed at the specified locations and orientations, it is then essential to rerun the risk models to confirm the coverage of hazards.

Installation should then be followed by a loop test and Site Acceptance Test (SAT) to confirm that the detectors are functioning as per design intent.

Operation and maintenance

After successful completion of SAT, gas detectors should be put into normal operation. Throughout the operation phase regular functional tests have to be performed to ensure proper function of gas detectors. Successful function of a gas detector system not only depends on the function of the gas detectors, it also depends on the functions of the interfaces such as emergency shutdown, blow down system and ventilation, as well as utilities including an uninterrupted power supply. Signals activated by a gas detector will also provide insights into the facility’s maintenance schedule.

Similar to any other equipment, gas detector performance deteriorates over time. It may become aggravated further if gas detectors are installed in harsh environmental conditions. Gas detectors should be included in facility inspection and maintenance schedules, considering manufacture’s recommendations and the local environmental conditions. Depending upon the criticality some of the gas detectors may require replacements while others are taken out for maintenance.

As part of the maintenance activities, gas detectors must be calibrated at a definite frequency using the same gas that the gas detector is designed to detect. The calibration gas should contain the same mixture and concentration to those being monitored. Sometime this is not practical, in which case another gas mixture that gives a similar response to the target gas can be used. The calibration output then has to be corrected with a calibration or correction factor, generally provided by the manufacturer. After calibration, the calibration mixture gas has to be disposed of safely as per local regulatory requirements.

Conclusion

Unfortunately, many gas releases are not visible to the human eye. Further to this, our limited experience of gas behaviour and dispersion after release adds to the complication. In today’s world we rely on our experience with smoke clouds caused by fires to understand gas releases. It is worth note, however, that these are two different subjects, as thermal energy generated by fire dictates the behaviour of smoke clouds, which is not the case in gas releases. The gas release will have a high concentration close to the leak source and this reduces over distance, until the release reaches a point where harmful effects are unlikely.

Companies put a great deal of effort and resources into the planning and design of facilities and none are designed to leak. Unfortunately, some equipment still has the potential to leak, and a combination of minor leaks may lead to major accident. Having an effective gas detection system in place, therefore, could prevent and mitigate the major consequences.

It should be understood that the intention is to achieve excellence and optimise spending. Sound integration between safety and operations can lead to cost savings in production, replacement, insurance and lost time. It is necessary to develop solutions that are supported by an appropriate business strategy that includes the necessary policies, regulations and tools. Safety should no longer be perceived as a cost proposition. It adds value if it is understood, appreciated and applied consistently.

Published: 29th Oct 2014 in Health and Safety Middle East

Share this article

ABOUT THE AUTHOR

Ramanathan Somasundaram

Connect with Ramanathan Somasundaram

Visit Website

POPULAR POSTS BY Ramanathan Somasundaram

Article

Safety Hazard Detection

Get email updates

Sign up for the HSI newsletter

Keep up-to-date through the power of email with Europe's largest audited safety magazine - delivering the latest news and products to satisfy all your occupational safety needs.
  • This field is for validation purposes and should be left unchanged.

FEATURED ARTICLES

Article

 Thameslink Traffic Management Programme

Press Release

‘Working At Height’ Remains Biggest Danger

Press Release

“Uncertainty and Ignorance” Risks More Asbestos Deaths

Advertisement

SOCIAL MEDIA

HSI on Facebook

https://www.facebook.com/HSIMagazine/

Advertisement

SOCIAL MEDIA

HSI on Twitter

hsimagazine HSI Magazine @hsimagazine ·
25 Jan

Global gas sensing leader @ionscience has today formally announced the addition of a high-specification Particulate Matter (PM) sensor to its portfolio.

Read all about this exciting addition!
https://www.hsimagazine.com/press-release/worlds-best-performing-particulate-matter-pm-sensor-now-available-from-ion-science-ltd/

#hsimagazine #ionscience #particulatematter

Reply on Twitter 1618280038557970432 Retweet on Twitter 1618280038557970432 Like on Twitter 1618280038557970432 Twitter 1618280038557970432

Advertisement

SUBSCRIBE

Stay up to date with our newsletter

    • Keep up-to-date with Europe’s largest audited safety magazine

 

    • Delivering the latest news and products to satisfy all your occupational safety needs

 

This field is for validation purposes and should be left unchanged.

Subscribe

SUBSCRIBE TO HSI MAGAZINE

5 reasons to subscribe to our digital and print package

  • Stay up to date from anywhere in the world, with instant access to the latest issue straight from your phone, tablet or laptop.
  • Trust that you’re getting the best content from our range of internationally accredited authors.
  • Get full access to our archives and see how occupational safety has evolved with us over the years.
  • Enjoy our monthly newsletter curated with up-to-the-minute news and a selection of editor’s top picks.
  • Hot off the press and straight to your door – look forward to your own glossy copy of HSI, delivered five times a year
Subscribe View Subscription levels

STAY SAFE & INFORMED

Subscribe to the best health & safety articles, news, products and regulations

Find out more

Stay up to date with our newsletter

  • This field is for validation purposes and should be left unchanged.

ABOUT

  • About HSI International
  • Advertise
  • Contact Us

YOUR ACCOUNT

Sign In Register Account Subscribe to HSI

RESOURCES

Request Media Pack

CONNECT

ACCREDITATIONS

Copyright Bay Publishing 2023. All Rights reserved.

Designed & Built by:
  • Terms & Conditions
  • Privacy Policy
  • Cookie Policy
We use cookies on our website to give you the most relevant experience by remembering your preferences and repeat visits. By clicking “Accept”, you consent to the use of ALL the cookies.
Cookie settingsACCEPT
Manage consent

Privacy Overview

This website uses cookies to improve your experience while you navigate through the website. Out of these, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website. We also use third-party cookies that help us analyze and understand how you use this website. These cookies will be stored in your browser only with your consent. You also have the option to opt-out of these cookies. But opting out of some of these cookies may affect your browsing experience.
Necessary
Always Enabled
Necessary cookies are absolutely essential for the website to function properly. These cookies ensure basic functionalities and security features of the website, anonymously.
CookieDurationDescription
cookielawinfo-checbox-analytics11 monthsThis cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Analytics".
cookielawinfo-checbox-functional11 monthsThe cookie is set by GDPR cookie consent to record the user consent for the cookies in the category "Functional".
cookielawinfo-checbox-others11 monthsThis cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Other.
cookielawinfo-checkbox-necessary11 monthsThis cookie is set by GDPR Cookie Consent plugin. The cookies is used to store the user consent for the cookies in the category "Necessary".
cookielawinfo-checkbox-performance11 monthsThis cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Performance".
viewed_cookie_policy11 monthsThe cookie is set by the GDPR Cookie Consent plugin and is used to store whether or not user has consented to the use of cookies. It does not store any personal data.
Functional
Functional cookies help to perform certain functionalities like sharing the content of the website on social media platforms, collect feedbacks, and other third-party features.
Performance
Performance cookies are used to understand and analyze the key performance indexes of the website which helps in delivering a better user experience for the visitors.
Analytics
Analytical cookies are used to understand how visitors interact with the website. These cookies help provide information on metrics the number of visitors, bounce rate, traffic source, etc.
Advertisement
Advertisement cookies are used to provide visitors with relevant ads and marketing campaigns. These cookies track visitors across websites and collect information to provide customized ads.
Others
Other uncategorized cookies are those that are being analyzed and have not been classified into a category as yet.
SAVE & ACCEPT