SECTION THIRTEEN – HYDROGEN SULFIDE
13.0 General
Hydrogen Sulfide, also know as H2S, is a highly toxic, colorless gas, that is slightly heavier than air. H2S has an unpleasant odor, detected at low concentrations, which is characteristic of rotten eggs. Due to the rapid onset of olfactory fatigue and paralysis, odor should not be used as the warning for the presence of H2S. H2S may collect in low-lying areas, tanks, cellars or confined spaces, displacing oxygen and increasing the amount of H2S. H2S is soluble in water based and
oil based drilling fluids and will migrate as a gas out of the fluid while in tanks or pits.
H2S will burn producing a blue flame. Sulfur Dioxide (SO2), a very irritating gas with a pungent odor, is produced. SO2 is a colorless gas appreciably heavier than air.
Although the most obvious source of H2S on a drilling site is from the well bore or oil storage tanks, other sources where H2S can occur may be:
• When sludge in the bottom of water tanks is disturbed. Such tanks can include drill water tanks, pre-load tanks, or other water tanks where sludge can build up.
• When mud solids are cleaned from a drill mud tank.
Each company with operations where hydrogen sulfide could be encountered should establish an H2S contingency plan. The company should obtain or develop an H2S manual and follow appropriate regulations that include at least the following:
A. Physical effects of H2S, B. Pre-well planning,
C. Precautionary measures, D. Emergency measures,
E. Breathing apparatus,
F. Problems in respirator use,
G. First aid for hydrogen sulfide, and
H. Detecting and monitoring H2S.
13.1 Initiation of H2S Procedures
In some areas, H2S is a severe hazard, due to the serious effect exposure to even small concentrations can have. When exposed to H2S, the nasal organs can be temporarily deadened
to the extent that additional exposure is not realized. Due to this false sense of security, test any areas known or suspected to have H2S to ensure the area is safe.
Where applicable, rigs are equipped with H2S detectors. After testing the well for H2S, log the concentration on the tour report. If the concentration exceeds 10 ppm, cease operations until the well is killed with water or ammonia. Bring explosion-proof fans and respiratory protection to the well site if the concentration cannot be kept below 20 ppm.
The maximum safe working level for an eight-hour day is 10 ppm (average).
NOTE: Take care to monitor for H2S gas when working on a back-flowing water injection well or
during an acidizing operation.
Drilling operations encountering hydrogen sulfide (H2S) should be aware of the special materials, equipment, and personnel protection equipment required. Safety procedures should be initiated and training completed in advance of penetrating the shallowest zone suspected to contain hydrogen sulfide. If hydrogen sulfide conditions are unexpectedly encountered, precautions should be implemented as soon as possible.
13.2 Applicability
In oil and gas well drilling operations, severity of the environment shall be assessed. As a minimum, the following measures shall be implemented:
A. Personnel protection equipment and training should be provided if the work area concentration of hydrogen sulfide exceeds 10 ppm as an 8-hour time weighted average (TWA) or 15 ppm as a short-term exposure level (STEL) averaged over 15 minutes; or the
work area concentration of sulfur dioxide exceeds 2 ppm as an 8-hour TWA or 5 ppm as an
STEL averaged over 15 minutes.
B. Detection equipment should be provided if/when the action levels for H2S or SO2 are exceeded.
C. Equipment and materials shall be selected on the basis of resistance to sulfide stress cracking and corrosion.
13.3 Training
Training should be initiated and completed in advance of penetrating the shallowest zone suspected to contain H2S. Hydrogen Sulfide Safety instructors are persons who have successfully completed a course in hydrogen sulfide instructor training or have received equivalent instruction from a company-designated hydrogen sulfide safety instructor/trainer.
Training should include:
A. H2S and SO2 safe workplace practices (use the buddy system) B. Hazards, characteristics and properties of H2S and SO2.
C. Dangers of H2S and SO2.
D. Signs and symptoms of H2S and SO2 exposure. E. Sources of H2S and SO2.
F. First aid for H2S and SO2.
G. Locations and use of respiratory and other safety equipment. H. Locations of safe briefing areas.
I. Use of Detection equipment.
J. Types of and location of alarms.
K. General safety precautions for H2S.
L. Dangers of Confined space and enclosed facility entry procedures (if applicable). M. H2S and SO2 Emergency Drills.
N. Wind direction awareness and routes of egress.
O. Rescue techniques and first aid to victims of H2S and SO2.
13.4 Rescue/First Aid Procedures – Hydrogen Sulfide
The following are the rescue/first aid procedures for hydrogen sulfide:
A. Buddy system should be used when attempting rescue operations.
B. Put on rescue breathing apparatus before attempting a rescue. You, too, can be overcome
by H2S.
C. Remove the person immediately to fresh air. Have someone call an ambulance. D. If the person is not breathing, start artificial respiration immediately.
E. If the person’s heart has stopped, begin Cardio Pulmonary Resuscitation (CPR) immediately.
F. Keep the person warm.
G. Once a person is removed to fresh air and normal respiration is restored, keep the person under medical observation until released by a doctor.
13.5 Detection
An adequate number of fixed, portable or both types of detectors should be provided for the safety of personnel working. There should be a clear understanding of alarms and responsibilities when the alarm sounds. Fixed hydrogen sulfide atmospheric monitoring systems should include visual and audible alarm(s), located where the alarm can be seen or heard throughout the work area.
Detection equipment should be calibrated and serviced per manufactures recommendations. The following are H2S detection methods:
A. There are several ways you can be alerted to the presence of H2S gas. The scent is usually
the first and, unfortunately, sometimes the last indicator. You can smell as little as one part
of H2S per million parts of air. However, if the concentration of gas is in the 100 to 150 ppm range, the sense of smell is quickly lost, giving a false sense of security.
B. When testing for H2S gas, be prepared for deadly concentrations.
C. To determine the amount of H2S present in your work area, use one of the following means of detection:
1. Lead acetate ampoules or coated strips: These change color (usually turn brown or black) in the presence of H2S. The degree of color indicates the concentration. These
are not completely accurate and should be used only as an indicator for the presence of
H2S.
2. Electronic Detectors: This type of personal device is belt-mounted or hand-held and gives audible alarms (and in some cases a read-out) upon exposure to a predetermined level
of H2S.
3. Air-Sampling Gas Detector Tubes: The concentration of H2S is registered by the length of discoloration when air is drawn through the detector tube. There are several reliable makes and types available, but their accuracy depends on the training and practice of the operator. Tubes must be certified by NIOSH or other equivalent certifying agency.
4. Fixed Systems: In larger plants and fields, a fixed system of continuous monitoring is often used. Where these units monitor an area continuously, an alarm system will give warning when the H2S concentration gets above a certain fixed limit.
5. Sensors should be located at the following locations as appropriate:
• Bell nipple
• Mud-return line receiver tank (possum belly) and/or shale shaker
• Pipe-trip tank
• Well-control fluid pit area
• Driller’s/operator’s station
• Living quarters, if located in close proximity to the well
• All other areas where hydrogen sulfide may accumulate that are not part of the confined-space entry program
13.6 Properties of H2S
The following are properties of H2S: A. Color – Colorless.
B. Odor – In low concentrations, it can be very offensive and is commonly referred to smelling like “rotten eggs.” In high concentrations, it is odorless.
C. Vapor density - H2S is heavier than air. It will settle in low areas such as cellars, tanks, etc.
D. Boiling point – 76oF (-60.2o C).
E. Explosive limits – 4.3 to 46 percent by volume, in air. F. Auto Ignition temperature – 500oF (260o C).
G. Water-soluble – Yes (4 volumes gas in 1 volume water at 32oF (0o C).
H. Flammability – Forms explosive mixture with air.
13.7 H2S Exposure Limits
Where H2S is present, the following limits of exposure should apply. (Certain local or federal regulations may have different standards.)
A. Ceiling value = 10 PPM
B. Time weighted average (TWA) = 10 PPM
C. Acceptable maximum peak above the acceptable ceiling concentration for an 8 – hour shift is
15 PPM (10 minutes, once only, if no other measurable exposure occurs.)
13.8 Toxicity of H2S
The toxicity of H2S is defined below:
A. 1 ppm = .0001% (1/10,000 of 1%) – Can smell (rotten egg odor), no risk.
B. 10 ppm = .001% (1/1000 of 1%) – Allowable for 8 hours exposure over the allowable concentration, protective equipment will be necessary. Beginning or slight eye irritation.
C. 100 ppm = .01% (1/100 of 1%) – Kills smell in 3 to 5 minutes. May burn eyes and throat.
Coughing, eye irritation, within 2 - 15 minutes. Altered respiration, pain in the eyes and drowsiness after 15-30 minutes followed by throat irritation after 1 hour. Several hours exposure results in gradual increase in severity of these symptoms and death may occur within the next 48 hours.
D. 500 ppm = .05% (5/100 of 1%) – Lose sense of reasoning and balance. Loss of consciousness and possibly death in 30 minutes to 1 hour. Respiratory disturbances occur in
2 to 15 minutes. Need prompt artificial respiration.
E. 700 ppm = .07% (7/100 of 1%) – Will become unconscious quickly. Breathing stops and death results if not rescued promptly. Need immediate artificial resuscitation.
F. 1000 ppm = .10% (1/10 of 1%) – Unconscious at once. Permanent brain damage may result unless rescued promptly and resuscitation is administered immediately.
NOTE: ppm = parts of gas per million parts of air by volume. 1% = 10,000 ppm.
13.9 Breathing Equipment (SCBA)
A. Self Contained Breathing Apparatus (SCBA) should be selected based on the usage of the unit. For example, 30 minute SCBA rescue unit, 5 minute escape pack, and cascade work units.
B
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