Gas Well Blowout in Gao Qiao, Chongqing, China
23 December 2003
243 people died, 9,000 were injured, and 64,000 were evacuated

Brief Description
Many of the confirmed dead are children or elderly people who were unable to flee after the explosion. Those who did not escape in time suffered burns to their eyes, skin and lungs from the gas.

A gas well blowout in an underground well happened at 10:00 pm on Tuesday, 23 December. The disaster took place at Chuandongbei gas field in Gao Qiao town in the north eastern part of Chongqing province and resulted in the release of natural gas and hydrogen sulphide, which is highly toxic when inhaled. The blowout - the worst of its kind in China's history - is thought to be caused by a puncture to the highly pressurised gas well caused by drilling.

According to press reports, the accident occurred as a drilling team was working on the 400 meter deep well. The accident sent toxic fumes (sour gas - a high concentration of natural gas and hydrogen sulphide (H2S)) shooting 30 metres out of a burst well.

The explosion occurred late at night, while people in the neighbouring villages were sleeping and affected 18,000 families in the surrounding rural farming communities including the towns of Yihe, Shangba and Zishui. Xiaoyang village, the village closest to the explosion was the most devastated, where entire families were lost due to the inhalation of the toxic fumes.

As of 5 January 2004, 243 people have died from inhaling the toxic fumes, 396 people are still receiving medical attention of which 27 are said to be in a critical condition. Overall 9,000 people were poisoned.

About 64,000 people ran away from their native places into the downtown of Kaixian County. Many domestic animals were killed due to gas inhalation and crops have been contaminated. The poisonous gas made an area of 25 square km a death zone as many villagers were intoxicated by the fumes in their sleep.

Rescuers were only able to ignite the gas spewing from the well on Wednesday in an attempt to burn it off. Officials have criticized a slow emergency response as leading to more deaths.

Chinese insurers will pay the equivalent of about $48.3 million US to cover the losses, the insurance regulator said.

Personal Quotations from the Community Affected

One man in Xiaoyang village near the well told the Yanzhao Metropolitan Daily that the only reason he did not die was because he was evacuated with the drilling team, while those who remained in the village perished.

"If you were higher up on the mountain, then it was disaster because there was no place to run up there," Peng Bian said.

"Some people thought that they could just close the windows and wait it out, but that was disastrous too. So many people died in their homes."

"In this kind of disaster, the township must tell the village and then the village leader must tell the villagers. The result here was that there was no notification at all, it is just chaos, so people died."

Chilling accounts have appeared in state media of emergency crews finding silent villages strewn with bodies of adults and children, some overcome as they tried to flee along mountain paths.

Survivors described the gas as an acrid black fog that clung to the ground, choking them and burning their eyes and skin.

Possible Causes

A five-day investigation by a State Council team found the disaster "was caused by numerous acts of workplace negligence".

The investigation found that developers had underestimated production capacity of the well and were not technically prepared for a well producing so much gas with such a high sulphur content.

"Moreover, workers on site did not follow operational regulations strictly and did not allow enough time for sufficient drilling mud to circulate to control the pressure," the China Daily said.

Investigators also found that a pressure control valve had been removed mistakenly from equipment "which was the direct cause of the blowout going out of control", the Xinhua news agency said.

Sun Huashan, deputy director of the State Administration for Work Safety, told state television that a crew drilling in a natural gas field had misjudged the amount of gas in the well which burst.

He also said that after deadly fumes began to flow from the well, the team failed to ignite them immediately, which would have prevented them from spreading.

"This was an accident due to negligence. Those people who were responsible will be dealt with," Mr Sun said.

Historical Data

In 1982, an Amoco sour gas well blew out in Canada and pumped sour gas into the air for 67 days. Two workers were killed and thousands of people downwind of the blowout complained of headaches, irritated eyes, nosebleeds, flu symptoms and miscarriages.

If you know about more accidents with sour gas well blowouts, please send them to us at apell@unep.fr

What are the Toxic Fumes (Sour Gas)?

Sour gas is natural gas containing hydrogen sulphide (H2S), H2S is flammable, has a strong rotten-egg odour, and is poisonous to animals and humans.

How toxic is H2S?

H2S may be deadly to people and animals within minutes at concentrations of 750 parts per million or greater.

Exposure to H2S can produce adverse effects on human health and behaviour, depending on concentration and length of exposure. Some scientific references have reported exposure to concentrations of H2S as low as one part per million can affect the central nervous system, resulting in neuropsychological effects; however, there is not scientific consensus on this point.

Accidental releases of sour natural gas from the well/pipeline network could create potentially life-threatening hazards to persons near the location of the release. Due to the presence of hydrogen sulphide in the natural gas, the vapor cloud created by a release of gas to the atmosphere would be toxic as well as flammable. Persons inhaling air containing toxic hydrogen sulfide vapor could be fatally injured if the combination of hydrogen sulphide concentration and time of exposure exceeds the lethality threshold. If the cloud is ignited, persons in or very near the flammable vapor cloud could be fatally injured by the heat energy released by the fire.

Because H2S is heavier than air, it tends to accumulate in low-lying areas.

How the impacts could have been reduced?

A gas well blowout is an uncontrolled flow of gas, oil, or other well fluids from a wellbore into the atmosphere. A blowout usually results from a combination of factors, such as human error and equipment failure. If, for any reason, blowout prevention procedures fail, the best action to reduce the impact is to immediatly ignite the well (setting it on fire). Ignition converts the H2S to sulphur dioxide, which disperses more effectively because the heat carries it up, resulting in lower ground-level concentrations.

Preventing such accidents from hapenning includes actions from the company regarding high standards of equipment maintenance, training of operators on how to deal with such an operation, standard procedures for operational and emergency situations, enforcement of such procedures and a safety culture at corporate level.

Even if all prevention procedures are taken, there is no zero risk in industrial operations and emergency planning for accidents should be done.

The first best action to reduce the impacts of potential accidents is to keep people away from the source of the "accident". Normally the population should be in a "safe" distance so that if an accident takes place, the distance itself will diminish the effects of the accident, by not reaching out the public with a lethal effect. In this specific accident the population was as close as 50 meters from the site, which increased the number of affected people.

The second best action to reduce the impacts of potential accidents is to respond to them in a quick and efficient way. How the first response to the accident is handled will determine the potential damage of the impacts.

The third best action, is of course, to be prepared for the accident.

To have effective preparedness in place is not only to prepare emergency response plans but to prepare them through a multi-stakeholder group gathering people from all the different "responsible" parties. This group should include industry representatives, local government representatives, community representatives, rescue services representatives, hospital representatives, local environment and planning agencies representatives, etc. The major responsability of this group is to develop an integrated emergency response plan where coordinated action on how to respond to potential accidents should be outlined.

This plan will be the basis for coordination and response if an accident that was identified as a potential scenario actually happens. The plan should then be tested and drilled, so that the community is trained on what to do when an accident happens. Public awareness raising campaigns should also be promoted, so that the local community is informed of what can potentially happen and how to react. If such a plan is in place, and an accident happens, then it is expected that there will be a coordinated, quick and efficient response, the community will know when and how to react, infrastructure will be available, and many lives will be saved.

This is what APELL is about, to increase community awareness and to prepare co-ordinated emergency response plans involving industry, government, and the local community, in the event that unexpected events should endanger life, property or the environment. It's too late to plan for an accident after it happens.

More information on APELL can be found on this site.

International Guidance on Gas Drilling

Listed below are a number of documents the oil and gas industry makes use of to safely manage drilling operations (in particular where H2S may be an issue):

American Petroleum Institute Publications:

  1. API Recommended Practice 49, Recommended Practice for Drilling and Well Service Operations Involving Hydrogen Sulfide
    Recommendations set forth in this publication apply to oil and gas well drilling and servicing operations involving hydrogen sulfide. These operations include well drilling, completion, servicing, workover, downhole maintenance, and plug and abandonment procedures conducted with hydrogen sulfide present in the fluids being handled. Coverage of this publication is applicable to operations confined to the original wellbore or original total depth and applies to the selection of materials for installation or use in the well and in the well drilling or servicing operation(s). The presence of hydrogen sulfide in these operations also presents the possibility of exposure to sulfur dioxide from the combustion of hydrogen sulfide.

  2. API Recommended Practice 54, Recommended Practice for Occupational Safety for Oil and Gas Well Drilling and Servicing Operations
    Includes procedures for promotion and maintenance of safe working conditions for employees engaged in rotary drilling operations and well servicing operations, including special services. Applies to rotary drilling rigs, well servicing rigs, and special services as they relate to operations on locations.

The International Association of Oil & Gas producers (OGP) Reports:

  1. Drilling Safety Guidelines Incorporating Safety Audit Check-Lists for Land and Offshore Rigs (Report Number 161)
    These guidelines provide the basic elements of a sound safety programme and illustrate the minimum level of detail required.The guidelines specify the responsibilities of contractor and company personnel and spell out the procedures expected from both parties in ensuring safety and in handling emergencies. In addition the guidelines outline the contents of a safety manual that every contractor should possess. The report concludes with comprehensive safety audit check-lists for both land and offshore rigs.

  2. Guidelines for Planning, Drilling and Testing of High Pressure Wells (Report Number 175)
    This report establishes principles and general guidelines for planning, drilling and testing high pressure wells. In response to the recent increase in offshore high pressure exploration drilling, much of the detailed material refers to equipment and procedures applicable to drilling from floating units. The principles and experience reflected in this document, however, should be applied to high pressure drilling worldwide both onshore and offshore. The document is in the form of a check-list of concerns to be addressed by the operator, and a series of examples of decision charts illustrating how these concerns can be systematically addressed.

  3. Guideline for underbalanced operations (Report Number 263)
    In the expectation that the applications of underbalanced operations will continue to increase, this report aims to establish international guidelines for selecting, planning, drilling and completing onshore and offshore wells where there is potential for hydrocarbon production. The guidelines are not intended to cover operations in non-hydrocarbon bearing zones.

The International Association of Drilling Contractors (IADC) publications and programmes include:


  1. IADC's HSE RIG PASS. This is an accreditation system designed to identify core elements of training programs for new rig employees and to provide a means of recognizing training programs that adhere to those elements.

  2. IADC's UBO RIG PASS. Similar in structure to HSE RIG PASS, this system provides core elements of training programs for rig employees employed in underbalanced drilling operations.

  3. IADC's Well Control Accreditation Program (WellCAP). This program accredits institutions providing training in well control. Curricula guidelines are provided for both fundamental and supervisory well control, subsea operations, workover, wireline, and coiled tubing operations.

  4. IADC Accident Statistics Program (ASP). ASP allows drilling contractors to benchmark their safety performance against that of their peers, on a global or regional basis.


Specific publications on the issue are:
- Drilling Rig Safety Inspection Checklist;
- Accident Prevention Reference Guide (a revised version is currently being prepared for publication);
- H2S Safety Handbook, and
- IADC Drilling Manual.
The IADC Publications Catalog, along with ordering information, is available on the IADC website

In addition, some companies follow the general considerations set out in the Texas Administrative Code (Rule 3.36) (available on line).

U.S. Department of Labor, Occupational Safety and Health Administration
Oil and Gas Well Drilling Safety and Health eTool. This eTool identifies common hazards and possible solutions to reduce incidents that could lead to injuries or fatalities (available on line). It has a specific feature on H2S Special Precautions.

Links and Sources

Relief web, part of the UN Office for the Coordination of Humanitarian Affairs (OCHA)
The International Federation of Red Cross and Red Crescent Societies
Xinhua Agency
Planet Ark News
BBC News

The International Association of Oil & Gas producers (OGP)
Oil and Gas UNEP library

International Association of Drilling Contractors

If you want to send us your comments, please e-mail us at: apell@unep.fr.