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Hazard Detection

Published: 18th Aug 2014 in OSA Magazine

Measures and systems to prevent confined space deaths

Industrial accidents happen due to unsafe working conditions, and confined spaces are one of the most dangerous industrial examples. Special caution must be taken when working in a closed, unventilated area, because the hazards are often invisible, odourless, fast working, and difficult to escape from. Even empty and well cleaned confined spaces can pose risks.

Defining confined space 

The term confined space refers to an area that is enclosed with limited access. An example is the inside of a storage tank, where workers may enter to carry out maintenance tasks, although it’s not ordinarily a regular space to enter.

Hazards in a confined space often include suffocation by asphyxiates or dangerous gases which may be present, submersion in liquids or other free flowing chemicals, petrochemicals or grains, and sometimes even electrocution, depending on the industry. 

Case studies

One of the very common examples of a confined space can be found in a factory where tank containers are manufactured, repaired, stored, cleaned or transported. In a factory of this kind a worker was carrying out manual cleaning work inside an ISO tank. He was found unconscious inside the tank and his co-workers quickly extricated him from the tank to administer first aid, but to no avail. The cause of his death was asphyxiation.

There are numerous cases of incidents where co-workers trying to save a colleague have been fatally trapped. This happened in a confined space where there was an accidental release of chlorine gas. All three employees were working on maintenance of the chlorine buffer vessel. The proper procedures were followed, but they didn’t use a gas detector before they started working on the tank.

Examples of confined spaces include: Utility tunnels, the inside of boilers (only accessible when the boiler is off), the inside of fluid storage tanks, septic tanks that have contained sewage, and small underground electrical vaults. Ships and other vessels also commonly have confined spaces.


The following occurences undoubtedly offer a terrifying pause for thought: 

  • Fire and explosion, OSHA 1982a – 50 confined space incidents from 1974 to 1979, with 76 fatalities. The majority of incidents were caused by worker error or faulty equipment
  • Lockout Tagout, OSHA 1982b – 83 confined space fatalities from 1974 to 1980.This category covers conveyor belts and machinery on the factory floor that are not generally considered confined spaces, but which satisfy the criteria for a confined space
  • Grain handling, OSHA 1983 – 105 confined space incidents from 1977 to 1981 with 126 fatalities
  • Toxic and asphyxiating atmospheres, OSHA 1985 – 122 confined space incidents from 1974 to 1982 with 173 fatalities
  • Welding and cutting, OSHA 1988 – 217 incidents from 1974 to 1985 with 262 fatalities
  • OSHA reports of welding and cutting deaths do not record whether or not an incident has occurred in a confined space, but it is estimated that 22% of the incidents were in a confined space
  • Shipbuilding and repair, OSHA 1990 – 151 incidents from 1974 to 1984 with 176 fatalities. OSHA reports of shipbuilding deaths do not record whether or not an incident has occurred in a confined space, but it is estimated that 36% of the incidents were in a confined space
  • Mining, MSHA Report 1988 – 38 confined space incidents from 1980 to 1986 with 44 fatalities

According to data collected by the US Department of Labor, Bureau of Labor Statistics. Census of Fatal Occupational Injuries programme, fatal injuries in confined spaces fluctuated from a low of 81 in 1998 to a high of 100 in 2000, averaging 92 fatalities per year during the five year period. 

Confined hazards

There can be various hazards in a confined space depending on the type of work but they are mainly:

  • Asphyxiation
  • Electrocution
  • Shock
  • Fire and explosion

Injuries and fatalities involving confined spaces are frequent. They often involve successive fatalities when would-be rescuers succumb to the same fate as the initial victim. Approximately 60% of fatalities involve would-be rescuers and more than 30% of fatalities occur in a space that has been tested and found to be safe to enter. 

Such accidents on the job are not only expensive for the employer, but are painful tragedies for the individual’s family members and colleagues. The fines from regulatory authorities vary from country to country, but they are always huge.

The major dangers of working in confined space are summarised below.

There may not be enough oxygen to breathe. Chemicals or gases may consume oxygen or displace it. Even if there is enough oxygen when you enter, it can be used up quickly just by breathing, or from your work.

Fires and explosions can happen more easily in confined spaces. Cigarettes, static electricity, sparks and heat can ignite invisible vapours and gases. Fires and explosions are dangerous in themselves as they are capable of consuming oxygen so quickly that escape is rendered impossible.

Toxins in the air can harm your respiratory and nervous systems. Often, you cannot see or smell these toxins and by the time you feel their effects it may be too late.

Physical dangers, such as entanglement in moving parts like agitators and blenders, can suffocate or crush you. Loud noise, intense heat and falls can also be dangerous.

Prevention is better than cure 

Confined space accidents are of particular concern in occupational safety and health, because often multiple casualties occur when untrained rescuers succumb to the same hazard as the initial victim. 

Confined space training outlines the skills and protocols for safe entry to confined spaces. It includes such precautions as lockout and tagout of any connecting piping, testing of breathable air quality, forced ventilation, observation of workers in the space, and a predetermined rescue plan with appropriate safety harnesses and other rescue equipment in place. 

The following steps should always be followed before the start of work in a confined space:

  • Internal or external certification of non hazardous atmosphere by a trained or competent person is required before personnel may enter a confined space
  • Work permit system with special job safety analysis of confined space
  • Lockout and tagout indication on work permit required or not
  • People entering the confined space should be trained in the companiy’s safe work procedures related to maintenance or mechanical integrity aspects
  • Local regulations should be under compliance by employer and employees with regard to confined space entry
  • Confined space entry programmes for each piece of equipment should be prepared and followed
  • Administration, supervision, training and auditing should be a top priority for confined space jobs
  • Personal Protective Equipment (PPE)should be applied before entering in confined space
  • Signage such as ‘Prohibited Entry’ should be placed on confined spaces
  • Oxygen monitors and gas detection instruments should be carried during the job, as per the type of confined space and nearby release sources
  • Emergency respirators should be available during the job
  • An emergency rescue plan and team should be available and properly in place before the job starts
  • The employer should ensure that atmospheric testing is performed in the following sequence before entering the confined space: oxygen content, flammability, toxicity

The safety of a person is not limited to the above steps. In addition to the above, understanding gas detection systems is extremely important. These should be always carried to detect the concentration levels of dangerous gases in confined spaces, even when you have already opted for all the other safe procedures.

Safety technology

Gas detection technology is widely used in industry to protect people, plant and the atmosphere from the damage that would take place due to a release of flammable or toxic gases and vapours. 

A gas detector is usually part of safety engineering system, and is a device that detects the presence of various flammable, toxic and normal gases within the area targeted.

This instrument can detect gas leaks from a storage vessel, pipeline, pump or applicable process equipment and sends a signal to control system so that the process is automatically turned off to make the situation safe.

During detection it also gives off an alarm so that people can leave the area immediately. Gas detection systems form an integral part of plant safety. Their main function in the plant is to detect the concentration of toxic and/or combustible gases and initiate an alarm or shutdown functions at a predetermined level – and at a stage sufficiently early to protect both lives and assets.

The gas detection varies for different types of gases, with single gas and multi gas dectectors available on the market.

Gas detectors are usually battery operated. When dangerous levels of gas concentrations are reached and detected they transmit signals through a series of audible and visual devices, such as alarms and flashing lights.

When detectors measure a particular gas concentration, the sensor responds to calibrated gas, which acts as the scale. When a sensor’s detection exceeds the preset alarm level, the alarm or signal gets activated. The alarms are set on the LEL (lower explosive limit) concentration level, generally measured firstly as low alarm activation e.g. 20% of LEL, and secondly as high alarm activation on e.g. 40% of LEL. This may be defined in the design philosophy of your project, or be demanded by your hazard identification study.

A complete gas detection system should consist of hazardous gas detection configurations, ranging from a variety of fixed gas combustible and toxic gas detectors to a complete line of display transmitters, gas controllers, power supplies and gas control panels

The method employed to monitor leakage of hazardous gases is to place a number of sensors at the places where any leaks are most likely to occur, as indicated by your hazard identification study or other specified requirements. 

These sensors are often then connected electrically to a multi-channel controller located some distance away in a safe, gas free area with display and alarm facilities and event recording devices. This is often referred to as a fixed point system. Being a fixed system it is permanently located in the area such as an offshore platform, oil refinery or laboratory cold storage – wherever gas leakage may present a problem. 

Gas detectors are of two types: portable devices and fixed detectors. The first is used to monitor the atmosphere around personnel and is worn on clothing. A portable detector is also used during shutdown operations or maintenance operation. 

Important definitions

  • Alarm – An audible or visual means of indicating equipment or process malfunction, or abnormal conditions to the operator
  • Alarm system – The collection of hardware and software that an alarm state transmits. The message should be displayed to the operator, recorded and an alarm report generated
  • Auto-ignition temperature – Lowest temperature at which there is enough heat energy to ignite vapours spontaneously
  • Flammable gas – A flammable gas is one than can burn when brought into contact with heat or flame
  • Flammable liquid – A flammable liquid is defined as having a flash point below 100°F (37.8°C) with a vapour pressure not exceeding 40 psi (276kPa). It is volatile by nature, constantly giving off vapours heavier than air that cannot be seen with the naked eye
  • Lower explosive limit (LEL) – This is the minimum concentration of flammable gas or vapour mixture that will propagate flames when exposed to a source of ignition. Commonly abbreviated to LEL or LFL (low flammable limit), a mixture below this concentration level is considered too ‘lean’ to burn. An increase in atmospheric temperature or pressure demands a decrease in the LEL of gas or vapour
  • Upper explosive limit (UEL) – This is the maximum concentration of gas in air that will produce a flash of fire when an ignition source is present. Any higher percentage of combustible gas or lower oxygen in the mixture of the two and the mixture will be too ‘rich’ to sustain combustion 

Published: 18th Aug 2014 in OSA Magazine


Sanjeev Paruthi

Mr Sanjeev Paruthi is a postgraduate Chemical Engineer from Punjab University Chandigarh (India), and is presently associated with a multinational EPC Company as its HSE and Process Safety Engineer at Gurgaon-India.

His experience of six years comprises of working with Hindustan Zinc Limited, Tata Coffee Limited and with leading consulting and Training Company in the domain of Process Safety/Risk Management. He also holds PG Diploma in Business Management from ICFAI. He is also pursuing an Advance Diploma in Industrial Fire Safety Management from Mohali Punjab, India.

Mr Paruthi has wide range of consulting and training experience for working with Chemical, Fine Chemical, Refinery, Petrochemical Storage Installations, paints and allied chemical industries. He has also designed Fire Prevention and Detection systems for Refinery in his current company. He has led various HAZOP and HAZID sessions and prepared various HSE documents under a refinery project.

Mr Paruthi has also conducted Operational Process Safety Studies.

His technical expertise is in the following domain areas:
• Quantitative Risk Assessment, HAZOP Studies, Process Hazard Analysis
• Fire Risk Assessment
• Process Safety Training and Development
• Process Safety Management Studies and Audits
• SIL Studies
• Hazardous Area Classification
• Static Hazards Evaluation
• Lockout Tagout
• Chemical Handling Safety (Gas/Vapour/Dust)

Sanjeev Paruthi




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