Overcoming confined space hazards

July 1, 2007
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In Kentucky, a police officer and two sewer workers were overcome by gas at the bottom of an underground pumping station while attempting to rescue a third worker. All four were pronounced dead at the scene.

At an Oklahoma wastewater treatment plant, one worker died of asphyxiation and another was injured after entering a confined space. OSHA cited the victims’ employer for not providing appropriate equipment and training.

Confined space entry presents a potential hazard in numerous industries. Whether you are inspecting an aircraft fuel tank, entering the hold of a barge, working in an underground utility vault or cleaning a wine fermentation tank, education and safety are crucial when entering confined spaces. Confined space incidents frequently have many common factors, even if they take place under very different circumstances. Unfortunately, many incidents claim multiple victims because, in addition to the initial casualty or casualties, would-be rescuers are also killed or injured.

Establishing and adhering to safe confined space entry procedures is a must. When entering a confined space, workers must be properly trained and equipped, and procedures followed.

Define “confined”
According to OSHA, a confined space is defined by three factors:

1. The space must be large enough for a worker to enter;

2. It cannot be designed for continuous worker occupancy;

3. A confined space has limited openings for entry and exit.

Permit-required confined spaces may contain known or potentially hazardous atmospheres. There may also be material with the potential for engulfment, inwardly sloping walls or dangerously sloping floors. Any additional serious safety hazards also require a permit before confined space entry. Employers must clearly identify permit-required confined spaces by posting danger signs.

Confined spaces can contain toxic hazards that can only be detected through testing. Oxygen (O2) deficiency, hydrogen sulfide (H2S), carbon monoxide (CO) and methane (CH4) are common hazards in confined spaces that can be detected with a portable gas monitor. Depending on the industry, other gas hazards may be present. For example, in the beer and winemaking industry, carbon dioxide is a serious hazard because it is produced as a by-product of fermentation.

Common hazards
An oxygen-deficient atmosphere can be the result of oxygen displacement by a toxic or inert gas. Microbial action, oxidation caused by rusting metal, combustion and absorption can also create an oxygen-deficient environment. Air is generally considered to be oxygen deficient whenever the concentration is lower than 19.5 percent v/v. Impaired judgment, increased pulse and respiration rate, fatigue and loss of coordination can occur when oxygen levels fall between 19.5 percent and 12 percent. Between 6 percent and 10 percent, nausea, vomiting and a loss of consciousness leading to death are possible.

Another confined space hazard is the possible presence of H2S gas. H2S is produced as a by-product of microbial activity. At very low concentrations, H2S smells like rotten eggs. However, at slightly higher concentrations, people rapidly lose their sense of smell. Relying on a portable gas detector for H2S readings — and not sense of smell — is the most reliable method of ensuring that workers are notified well before dangerous levels are reached. In a range of 200 to 300 ppm, eye inflammation, respiratory tract irritation and a loss of consciousness can occur. When levels of H2S reach 500 to 700 ppm, death will occur within 30 minutes to an hour.

Because H2S is heavier than air, it can collect in low lying areas and confined spaces. Knowing the vapor density of gases can be heavier or lighter than air means it is essential to test at various levels in a confined space. Stratified testing prior to entering a confined space will alert workers to potentially dangerous environments. A confined space gas detector kit makes stratified testing easy and generally includes a multi-gas monitor with pump, 10-foot sampling hose for pre-testing (longer lengths available), spare batteries (rechargeable or alkaline), quad-gas cylinder for bump testing and calibration with gas regulator, all conveniently contained in a rugged carrying case.

Besides H2S, the decomposition of organic waste materials can also produce methane. Leaks in gas pipelines can be another source of methane in confined spaces. Although methane is the most commonly encountered combustible gas hazard, it is important to monitor for additional combustible gases. A combustible sensor that reads in the %LEL range is excellent for measurement of methane, propane and other common combustible gases that are not detectable by PID.

Carbon monoxide, which is produced as a by-product of incomplete combustion, presents another hazard in confined space entry. The internal combustion engine exhaust from vehicles, pumps and compressors running in the vicinity of a confined space can create a build-up of carbon monoxide. A concentration of only 1,600 ppm can be fatal within hours. Even lower levels of exposure can result in death if there are underlying medical conditions or when there are additional factors such as heat stress.

Sensor selection
A portable multi-gas detector with H2S, CO, O2 and combustible (%LEL) sensors is ideal for the majority of confined space entry applications. A five-gas monitor can provide an extra sensor to protect against other potentially deadly hazards that are specific to a jobsite or industry. Adding a non-specific PID sensor allows detection of a broad range of dangerous volatile organic compounds (VOCs). In some European countries, it is also mandatory to monitor for CO2 in confined spaces. The types of sensors selected should reflect the known and potential atmospheric hazards associated with the environment to be monitored.

After initial testing is complete, testing of the atmosphere within the space must continue to ensure the area remains safe. If a hazardous atmosphere is detected during entry, employees should exit immediately, re-evaluate the space and take corrective measures.

Do not rely on human senses for detection of potentially harmful gases in confined spaces. Multi-sensor confined space instruments are increasingly compact, rugged, easy-to-use and much less expensive than ever before. Any confined space entry program must include the use of properly maintained gas detectors. Given the human costs associated with a confined space incident, using a confined space monitor could be your wisest decision.

SIDEBAR: Permit required?

An employer must determine whether a confined space meets the criteria for being “permit required.” A permit-required confined space must:

  • meet the definition of a confined space, then
  • contain or have potential to contain a hazardous atmosphere, OR
  • contain or have potential to contain an engulfment or entrapment hazard, OR
  • contain physical hazards, OR
  • other serious safety and/or health hazard not in any of the three above.


Permit-required confined space entry requirements:

  • complete permit application
  • identify work to be performed and estimate time to complete
  • perform special requirements, such as lockout, ventilation, etc.
  • take and record air monitoring readings
  • ensure monitors are charged and within calibration dates
  • ensure monitor sensors are not compromised
  • designate an assigned attendant
  • signature of authorized supervisor after review of permit
  • post permit at entry of space
  • advise confined space rescue personnel of entry
  • follow established procedures


Permit-required confined space duties include:

  • eliminate or reduce exposure to known hazards prior to entry
  • may re-classify to non-permit required space if hazard(s) is removed
  • entrants, attendant, supervisor with knowledge of hazards present
  • maintain communication link with attendant and each other
  • exit upon monitor alarm or attendant instructions to evacuate space
  • ensure all entrants are accounted for upon space exit
  • return permit and monitor to storage area when work is complete

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