PLANNING, TRAINING, EQUIPMENT ALL CRUCIAL IN H2S BLOWOUT

L. William Abel
Wild Well Control Inc.
Spring, Tex.

An offshore blowout with hydrogen sulfide (H2S) gas present requires special procedures and highly trained personnel to control the well quickly and safely.

Toxic gas clouds from a blowing well can accumulate in low areas, causing more danger. Thus, the blowing well may need to be ignited to burn the H2S So the well can be controlled safely.

Any policy regarding work practices in an area where H2S is present or is a potential hazard must take into account the basic characteristics of H2S and general industry practices. In sufficient concentrations, H2S is extremely dangerous to personnel and equipment (Table 1)(17687 bytes). Work in high concentrations of H2S should only be attempted by highly trained specialists.

The intervention plans and procedures must take into account the properties of H2S:

In low concentrations, H2S smells like rotten eggs. Because H2S rapidly deadens the sense of smell, one should not depend on smell alone to detect H2S. Appropriate permanent, portable, and personal monitors should be used.
H2S is colorless and extremely toxic.
Although H2S is readily dispersed by wind, it is heavier than air and tends to settle in low areas.
H2S is flammable at concentrations of 4-45 vol %. It burns with a blue flame, producing sulfur dioxide (SO2), which is also a toxic gas.
H2S is highly corrosive to certain metals (especially electrical contacts).

H2S poisons by paralyzing the nerve centers that control breathing. Four factors affect an individual's reaction to H2S exposure: duration of exposure, frequency of exposure, H2S concentration, and individual physiology.

Industry and government have set acceptable limits for working in areas where H2S exposure is possible. The most broadly accepted guideline at present states that, for individuals in good general health and with no history of physiological complications, the acceptable 8-hr, time-weighted average for continual exposure to H2S shall not exceed 20 ppm.

A continual on-site monitoring program for the entire work area should be a matter of policy. The equipment should monitor for all expected types of toxic gases that could harm personnel or the platform.

Various protective breathing systems (such as filtration gas masks, escape packs, self-contained pressurized breathable air systems, and cascade breathing air systems) are each suited to particular operations, such as evacuation from a contaminated area, rescue efforts or remedial work, work in high levels of H2S, and rapid evacuation.

PERSONNEL MANAGEMENT

Because of the extreme potential for a toxic gas disaster, all personnel who board an offshore facility with H2S potential should meet certain minimal qualifications for health and training. All personnel working at the facility should receive basic training on H2S safety, breathing equipment operation, and location of safety equipment on the facility. The extent of training should be commensurate with the individual's job responsibilities and degree of exposure to H2S in the performance of his job.

If there is an H2S release into a safe area, a habit of reaction must be established for all personnel. It is essential that this pattern be adopted and followed in sequence, as it may mean the difference between life and death.

Listed below are key points for personnel action in order of importance:

Do not panic.
Go immediately to a location where breathing equipment is available (if possible hold your breath until donning the breathing equipment).
Don breathing apparatus or filtration mask.
Sound an alarm and alert facility management personnel (if not already done).
Rescue victims from contaminated area. Note: Rescue should only begin after donning 30-min, self-contained breathing apparatus and obtaining additional assistance (buddy system).
Revive victims.
Get medical aid.
Eliminate fuel and ignition sources to the affected area.
Evacuate all nonessential personnel from the facility.
Evaluate the situation and abandon the facility, if necessary.

A group of senior level personnel should be trained in toxic gas safety, testing procedures, and rescue techniques.

ESCAPE ROUTES

Because H2S exposure is so dangerous, there must be a contingency plan for evacuation and escape for the blowout intervention team.

Additionally, the safe areas must be so designed that they too can be cleared in case conditions change and cause H2S to accumulate there. Unless all personnel are under mask in a certain area, evacuation should be mandatory if the H2S level exceeds 20 ppm. Thus, strong consideration must be given to the method available for escape.

H2S is heavier than air and tends to settle in low places and confined areas. On an offshore facility, an H2S cloud will settle at the water line until dispersed by the wind.

An example of the disastrous effects of an ill-prepared evacuation took place in 1980 on an offshore drilling operation in the Arabian Gulf. An unanticipated expulsion of H2S and hydrocarbons during a trip killed the crew and rig supervisor on the rig floor. As panic spread, several of the rig personnel attempted to evacuate by climbing down the rig bow leg to the water. Unfortunately, 19 people died, 10 of whom were found floating in the water where they had been overcome by the H2S cloud. The survivors had moved to the upwind side of the rig and up to the elevated heliport deck.

The method of evacuation depends on the particular situation. Primary exit paths should be predetermined and used, unless they are blocked by fire, physical damage, a toxic gas cloud, or other obstacle. Should this primary path be unusable, a secondary path must be available.

The choice of equipment in the design phase should consider escape paths. Ladders and stairways should be carefully planned to allow the greatest freedom in gaining access to the evacuation pathways and equipment of choice. It is essential to keep in mind that personnel must attempt to gain access to the highest, least confined upwind path possible.

ABANDONMENT

Even a fully prepared and equipped intervention team should be ready to abandon the work area and even the facility if necessary. Abandonment of a facility for any reason must be carefully considered when operating procedures are developed. The safety of all personnel must be paramount to all material implications, but certainly an unwarranted abandonment could also cause unnecessary losses.

Thus, a strong and well-supported position must be established regarding the criteria for abandonment. Once this position is established, field personnel can feel comfortable in ordering an abandonment without a possible fatal delay. The key point is that the designated safe areas must be safe. The recommended guideline for abandonment of a safe area is when the H2S level exceeds 20 ppm. If this occurs, work must stop, and abandonment commenced.

There should be a small margin of time after H2S is first detected, however, to remedy a minor non-life-threatening expulsion of gas or to continue work where an unavoidable level of background gas is present because of the operation.

In the case of an abrupt H2S discharge, this level of contamination would be reached quickly, and there would be no question about the need for area evacuation or total abandonment. To aid in assessing and communicating the level and extent of H2S present, a set of classifications, such as the following, should be adopted:

H2S red
Because of the location of the toxic gas expulsion or weather conditions, the entire facility has been enveloped by H2S. Fire may be present or at least pose an additional threat to personnel. Work under mask is mandatory and only by trained professionals.
H2S blue
A significant expulsion of H2S has occurred, but conditions have limited involvement to only specific areas or sectors. The levels of H2S exceed safe breathing levels and require the use of breathing air systems only in the affected sectors. Working only under mask is required, but upwind areas of the facility are safe from involvement. Continual monitoring of wind conditions and the H2S levels outside the affected area should be maintained. Steps should be taken to evacuate the entire facility immediately if conditions deteriorate or wind direction changes.
H2S yellow
A limited expulsion of H2S has occurred, but the level (20 ppm H2S) does not exceed conditions that require the use of breathing air systems. Evacuation or abandonment of uncontaminated areas is not immediately necessary, but all personnel and support operations should be alerted of the potential danger and be ready to go to a condition blue.
H2S green
No H2S is present in the atmosphere, or it is being successfully dispersed through a downwind flare. There is still a potential hazard of an H2S expulsion, and periodic monitoring should continue.

Fig. 1 (123438 bytes) is a basic decision tree for H2S emergencies.

A documented abandonment plan should be prepared for the entire work site. The objective is to identify the area of toxic gas emission and move all personnel out of the hazardous zone. To establish the most logical path for evacuation and the extent of risk, the work area should be divided into sectors according to geographic location, anticipated areas of highest risk, and prevailing wind conditions.

To communicate the necessary emergency or evacuation information to all personnel, muster areas should be established at various points. Upon hearing an alarm or warning for a toxic gas emergency, personnel should immediately report to the nearest muster area for further information. Muster areas should be at the highest elevation possible, directly accessible to at least one method of evacuation, and upwind from anticipated sources of toxic gas. Alternate areas must be chosen in case an H2S expulsion contaminates a muster area. Each muster area should be equipped with adequate breathing equipment to facilitate escape should it become a contaminated area.

PERSONNEL RESCUE

If anyone has fallen victim to H2S, there should be a concerted but cautious attempt to rescue him immediately. The quicker a victim is rescued and resuscitation is begun, the better the chance for survival. The most important factor in a rescue attempt is not to cause another victim. The following points must be considered and followed in a rescue attempt:

No one is to attempt a rescue in an H2S-Contaminated atmosphere before donning breathing gear or without being accompanied by at least one other qualified person. A rescuer should never attempt a rescue without assistance from another worker who is fully prepared, is in close proximity, and has breathing gear on.
Effective communication must be present between the rescue team and the control center.
If possible, a rescue harness should be worn by the rescuer, in case he is overcome by H2S. The harness will allow other workers to recover him without subjecting them to the same conditions.
Given the danger and quick effects of H2S, any rescue attempts should be tempered by the risk to the rescuer, complexity of the effort, and evaluation of whether the person is already dead. Although callous, this view must be taken to avoid additional victims.
The rescue attempt should be performed quickly after the victim has been overcome. It must be remembered that death will occur after 30-60 min of exposure to a 500-ppm H2S concentration (Table 1)(17687 bytes). In 1,000-ppm concentrations, life expectancy is reduced to minutes. No attempt to perform cardiopulmonary resuscitation (CPR) or render first aid should be done until the victim is removed from the contaminated area.
CPR should begin immediately once the victim is removed from the contaminated area. The rescuer should remember that other trauma may have occurred as a result of a fall when the victim lost consciousness. These injuries must be considered secondary, because in most cases the effects of H2S Will be the most likely to cause death.
Medical assistance should be summoned immediately and the victim transported to a hospital.

BLOWOUT IGNITION

The decision to ignite a blowout voluntarily has some major implications, the gravest being that the situation may become worse, rather than better. The greatest concern is that ignition will damage adjacent wellheads on the platform, causing additional blowouts and fires. Further, this may cause the well control effort to be orders of magnitude greater than if a single well was blowing out but not on fire. A blowout should be ignited if it is thought that human life can be saved as a result.

When H2S is emitted from a blowout, the decision to ignite becomes somewhat less complex because of the imminent danger from the gas. What must be considered in the ignition of an H2S flow is the byproduct of the reaction, SO2, also a toxic gas. At 5 100 ppm, SO2 causes irritation of the upper respiratory tract, inflammation of the nose's mucous membranes, dry throat, cough, and eye burns. Higher SO2 levels or extended exposure can lead to death by asphyxiation, chronic pneumonia, or bronchitis.

Fire does not eliminate the danger; rather, it alters the characteristics of the flow. The downwind side of the blowout fire still poses a danger in the form Of SO2 and should be isolated from access by personnel and vessels. In certain situations, where H2S levels in the flow are not extreme, the SO2 released by burning may be manageable. In these cases, ignition may be the best option to minimize personnel risk. Under most conditions, it is not advisable to ignite an H2S flow unless lives are in danger.

Once the decision to ignite the flow is made, consideration then turns to the method. Although a remotely operated ignition system (similar to that used to ignite a flare) is an option, the risk of an unintentional or premature actuation because of panic makes this method undesirable. In most situations, the best alternative may be the use of a flare gun or similar device to ignite the flow from a boat on the upwind side, although access may be limited because of the H2S.

The ignition process requires clear, rational preparation to eliminate the risk of premature ignition. The following general procedure should be used for igniting a blowout:

Evacuate all personnel from the area, platform, or facility.
Make certain no vessels are within a minimum of 2 km downwind of the facility.
Close valves or other devices which may provide a possible fuel source or migration path for a fire or flow.
Evaluate wind and weather conditions to ascertain whether the situation can change to endanger personnel either on the platform or at an adjacent installation.
Attempt to determine the nature of the flow, its cause, probability of increased severity, and methods to stop the flow through short-term efforts.
Evaluate the preceding information to decide if ignition is justified. If the conclusion is yes, proceed with ignition.
Determine whether ignition using a flare gun is possible from the facility (that is, strong prevailing winds away from the firing position, H2S-free atmosphere from which to work, available cover from a flashback, and clear access for escape).
Call on a single vessel with a minimum crew to act as the firing point for the flare gun or other device.
Establish the range of the flare gun and whether access to the platform within this range is safe and possible considering the presence of H2S and heat radiation from the fire after ignition. Proceed if these conditions can be met.
Clear all personnel, aircraft, and vessels from within a 2-km radius of the platform except for the vessel required for a firing base.
Approach the platform from the upwind side, while H2S levels are continuously monitored. All personnel not required to operate the vessel should be removed. Once within safe range, one man should fire the flare gun and ignite the flow. Escape from the area should be made with haste because of the possibility of secondary explosions and falling debris.
Once ignition occurs, no attempt to board the facility should be made until the situation stabilizes and conditions permit access with reasonable safety.

Fig. 2 (167521 bytes) is a basic decision tree for ignition of flow in an H2S emergency.

An alternative method using a helicopter may be considered. In this case a flare gun would be used to ignite the flow.

WORK GUIDELINES

The blowout intervention team will typically consist of a team leader, two or three well control specialists, and one or two H2S/well control specialists with medical training. These men will conduct the majority of the operation with only limited assistance from roustabouts or other personnel. If outside workers are used, they should be carefully chosen, trained, and supervised during their short-term assignments.

Guidelines for operations and personnel safety must be set for work within the danger zone. The following is a basic list that should be expanded to fit particular situations:

Prior to commencement of each day's operation, the tasks, responsibilities, procedures, equipment requirements, and contingency plans should be reviewed with the intervention team, company officials, service organizations, and safety personnel.
Work by the intervention team should be limited to daylight operations only until the H2S flow is safely under control and operations can return to a normal pattern.
Weather conditions in the area should be monitored constantly to determine if conditions are favorable for the day's activities.
All equipment to carry out the planned work must be inspected and ready for deployment prior to commencement of work.
Access to the area or the facility should be restricted to only essential personnel, vessels, and aircraft.
Breathing and safety equipment should be thoroughly inspected and available in adequate quantities to support the entire operation.
Communication among the intervention team, offshore command center, on site vessels, and onshore base should be tested.
Doctors and medical facilities should be available aboard a vessel posted outside the restricted area, with a helicopter and rescue vessel available for immediate response.
All personnel who may be required to work within the danger zone should be required to take suitable training in H2S safety.
A buddy system should be fully implemented and assignments given to ensure each man working in the danger zone has at least one person guarding his safety.
If an equipment failure, shortage of breathing air, minor injury, or other event that may inhibit one of the safety measures occurs, operations should cease and the intervention team withdrawn until corrective action is taken.
Each man working in the danger zone on a breathing system should be restricted to a maximum of 2 hr strenuous labor without a break, if conditions permit. This restriction is necessary to avoid mistakes from fatigue and stress.
Vessels entering the danger zone should be required to have H2S monitoring devices and breathing equipment to support the crew. While the vessel performs critical operations, an H2S technician or medic should also be onboard to assist the crew.
Before a helicopter is allowed to land or approach any point on the offshore facility, the wind, lower explosive limit, and H2S levels must be favorable.
Fire water monitors should be ready and manned to provide water cover to personnel in case of accidental ignition.

INTERVENTION

There are certain basic requirements to support an intervention operation, but each situation may require additional equipment. The following items will be essential to the operation: two cascade breathing air systems to support six men for 12 hr; three self-contained breathable air (SCBA) units for each team member; SCBA replacement tanks for 4 hr air supply to each man; cascade replacement tanks for an additional 12 hr air supply for six men; communication devices that allow team members to talk with the command center and each other while masked up; high-volume breathing air compressor, safety harnesses, and hand tools; a minimum of three different types of H2S measuring devices; six intrinsically safe bug-blower fans to disperse gas in the work area; and cameras to record activities or equipment configurations for later review in planning work activities.

If the offshore facility has been completely abandoned, access to the platform and target area for men and equipment could be a major concern. Given favorable wind conditions, the intervention team should be able to board the facility with small equipment at a point upwind of the flow, either by helicopter or boat.

Access by helicopter is the fastest and best means to deploy intervention personnel, but the capability to deliver equipment is limited.

Approach by sea will be strongly influenced by wind conditions. Even then, to reach the deck it might be necessary to climb the platform leg with a breathing-air backpack. Use of the workboat receiving area with its cranes provides the best access for the heavier equipment to the platform, but only if power supplies to the cranes are operational.

Once onboard, the team can use alternate power supplies for permanent cranes or other mechanical means, to convey the necessary equipment to the deck. If possible, the majority of this activity should take place outside the high-level H2S cloud. Breathing gear should be readily available and the H2S levels monitored constantly, even if the H2S is within tolerable levels.

An important point for the intervention team and operator's personnel to consider is the possible corrosive effects H2S may have had on various metals and electrical equipment in the contaminated area. The metal used in electrical equipment is particularly susceptible to H2S corrosion and therefore subject to failure.

This problem occurred in the 1980 blowout example mentioned earlier. After the H2S flow had been diverted from the floor into a line exiting below the rig, the rig was restarted to strip in a kill string. Afterwards, casing was run and cemented across the H2S-producing formation. An inspection after the completion of this activity revealed that major corrosive damage occurred in motors and electrical contacts exposed to the H2S. Great expense and a 50+ day delay occurred before the rig was back in good working order. Electrical equipment exposed to H2S may not be safe and reliable. Therefore, if a restart of the existing drilling equipment is considered, a close inspection of damage from corrosion will be required.

Once the basic equipment to permit an approach to the high-H2S zone is onboard and rigged up, consideration may be given to investigating the flow. Each step in gaining this access should be carefully planned to ensure that adequate breathing air is available, clear evacuation paths are available, and. that each team member is backed up by another man.

Each man will use the communication equipment to report his progress or problems. If possible, the initial approach to the flow will be made through the bridge, using self-contained breathing equipment. This approach will limit the actual inspection period to only a few minutes.

During this time, the general layout must be surveyed, the flow situation investigated, and the state of the onboard cascade system inspected. Until reserve breathing systems can be brought into play, the initial efforts must be kept to Within safe time frames. As a cascade breathing system is Put in use, the work periods may be extended.

When the work reaches a point where heavy equipment must be transferred directly from a boat to the platform where the flow occurs, care must be taken to minimize the exposure of the vessel to dangerous gas levels. Timing to take advantage of favorable winds, preparations to make quick transfers possible, and close communication are the keys to this effort. A member of the intervention team should also be on the boat to aid and advise the crew. All crew members of the boat must wear breathing gear at all times within the danger zone.

The buddy system also applies to the vessel; it is attached by a tow line to a second vessel outside the danger zone. In this manner, if for some reason the equipment vessel lost power, had to shut down because of explosive limits, or the crew was overcome by H2S', the second vessel could drag them and the vessel to safety.