1. H2S in the Oilfield – Fact Sheet
Introduction to H2S
Hydrogen Sulfide, or H2S, is an ever-increasing
problem for workers involved in oil and gas
exploration and production.
H2S, however, is not just an oil field problem.
This gas is found in many areas unrelated to the oil
field, such as landfills, sewers, waste treatment
plants, and septic systems.
Where does H2S come from?
H2S is formed in the process of the natural decomposition
of organic matter. This is the reason that it shows up in
many different locations. Another source of Hydrogen
Sulfide is as a by-product during a reaction between any
acid and any sulfur compound.
Hazards of H2S
The hazards of Hydrogen Sulfide gas can be controlled through:
• Receiving adequate training
• Pre-job planning
• Emergency response planning
• Controlling hazards
• Following safe work procedures
• Using breathing apparatus
All of these activities are designed to ensure your safety when working in an area where
H2S may be present.

2. Operations involving H2S
Many oilfield operations expose workers to Hydrogen
Sulfide.
H2S can be found in the following type operations:
• Well Servicing
• Drilling
• Water Hauling
• Well Stimulation
• Production Operations
• Plant Operations
Sources of H2S
Oilfield workers can expect to find H2S at several specific locations involving different
types of operations.
Here are some examples of the specific locations where you
could expect to find H2S:
• Confined spaces
• Tank Batteries
• Shale shakers & mud pits
• Circulating tanks
• Wellheads
• Produced water
Liquids and H2S
Hydrogen Sulfide may be dissolved in liquids and then
released if agitated, depressurized, or heated.
This means that gas in the liquids is released when they
are circulated, pumped, flowed or swabbed into tanks.
This also applies to H2S in well bore fluids that are
agitated by these activities. That’s another reason why
you would expect to find Hydrogen Sulfide at the top of
open tanks, gauge hatches and vent lines.

3. Characteristic of H2S
It is important that you know the characteristics of H2S.
Knowing these Hydrogen Sulfide characteristics are valuable when you have to
evaluate a potential H2S hazard at your work location.
The characteristics of Hydrogen Sulfide are:
• It is Colorless – H2S cannot be seen as a gas.
• It can have a Rotten Egg Smell – Due to its sulfur
content, H2S has a distinctive smell.
o This smell is only apparent in low
concentrations.
o The olfactory nerve suffers fatigue at higher
concentrations, and the sense of smell is lost.
• H2S is also Flammable – H2S has a flammable range
of 4.3% to 46% in air, and an ignition temperature of
500°F. By comparison, the temperature of the tip of a
lit cigarette is over 700° F.
• H2S is Heavier than Air – H2S has a vapor density of approximately 1.19, which
makes it slightly heavier than air (1.00). This is why H2S settles in low areas.
• H2S is Water Soluble – H2S will mix into a solution with water, and will be carried
to the surface in produced water and drilling mud.
• It is also Corrosive – When H2S mixes with water, a weak hydrosulfonic acid is
formed. This acid will deteriorate metals with high iron content, creating Iron
Sulfide Scale. Also, this causes irritation of the eyes, nose, and throat areas of the
exposed person.
• And most important, H2S is Toxic – Hydrogen Sulfide ranks as the second most
deadly naturally occurring gas, behind Hydrogen Cyanide.
o H2S kills by paralyzing the nervous system area that controls the
involuntary function of breathing. The result is lack of oxygen to the brain,
followed by death in minutes.

4. Toxicity of H2S
As has been emphasized, H2S is extremely poisonous. Below is toxicity information for
H2S. It contains important information concerning H2S at different concentrations.
• At 1 ppm there is a detectable rotten egg odor
• At 10 ppm, that is the maximum allowable
exposure level and the alarm set point for
personal monitors.
• A concentration of 20 ppm will result in irritation
of the eyes, nose and throat areas.
• 50 ppm of H2S causes a loss of the sense of
smell, headache, and dizziness from lack of
oxygen.
• 100 parts per million is the IDLH or Immediately
Dangerous to Life and Health level for H2S. No
work is allowed without the use of the buddysystem.
• 200 ppm causes severe eye, nose, throat irritation, headaches, dizziness, and
nausea.
• When the concentration reaches 500 parts per million, unconsciousness occurs
within a few minutes along with respiratory paralysis, followed by death.
• At 1000 ppm the victim becomes unconsciousness immediately. Death results in
4-6 minutes, if not rescued promptly..
Corrosivity of H2S
Hydrogen Sulfide is highly corrosive. This may cause problems such as Iron
Sulfide Scale production, which is dangerous when disturbed.
H2S can be released back into the environment in dangerous quantities
during the removal of this scale.
Iron Sulfide Scale can also burst into flames if allowed to contact oxygen.
Hydrogen stress fractures can occur due to Hydrogen embrittlement, which
can cause failures of the metal components.

5. Detection Equipement
Many facilities will use some form of fixed monitoring devices to detect and alert
workers to the presence of Hydrogen Sulfide.
If a release occurs, the sensors will detect it, an alarm will
sound, and a light will usually flash.
These devices are placed with the sensors in the areas a
release is likely to occur, and the lights and alarms where
workers will be able to see and hear them.
The monitors commonly have alarm set points at 10 ppm
(low) and 15 or 20 ppm (high).
At times, it will be necessary to use personal monitors.
These devices are preset to alarm at 10 ppm, and
frequently come equipped with a light that flashes, a
beeping alarm, and a vibration alarm.
These are to be worn on the personal body, and outside all
clothing. It is recommended that they be placed up high on
the body, preferably within 18 inches of the nose and
mouth.
Respiratory Protection
When it is necessary to perform work in areas where the H2S
concentration is greater than 10 ppm, a positive pressure
respirator will be required. Negative pressure respirators shall
not be used in H2S environments.
Once a fit-test has been performed, it is necessary not to allow
the seal to be impaired by facial hair or glasses. Many locations
will not allow persons entry with improper facial hair.

6. Respiratory Equipment
One type of positive pressure respirator is the Air Line
or Cascade unit.
This device will provide the wearer with a clean air
source from compressed air cylinders and hose
assembly.
The benefits of this unit are that it will give the wearer
a steady supply of air for a long period of time.
An attendant will be required to monitor the air
available in the cylinders, and alert the wearer when
air reaches too low a level.
Problems with this type of unit include the hose
becoming tangled or kinked, and the need for possible
escape in a direction away from air supply, requiring a 5-minute escape bottle.
Another type of positive pressure respirator is the SCBA or SelfContained Breathing Apparatus. These units are more compact than
the Air Line units, and do not have the hose problems. However, they
are limited to a smaller air supply, which results in a shorter amount
of time available to the wearer. SCBA’s are usually rated for 30min or
45min, yet the actual time will vary with the wearer’s physical exertion
and conditioning levels. These units are equipped with an alarm to
alert the wearer when the air cylinder pressure is too low.
Emergency Response
Medical experts tell us that, without a continuous supply
of oxygen, the brain can only survive four (4) to six (6)
minutes. That is the reason it is so important to get the
H2S victim to a safe area as soon as possible.
At the pre-job safety meeting, the designated safe areas
should be established and a rescue plan be designed to
get the victim or victims to fresh air and resuscitate them
within 3 minutes.

7. If someone is overcome by H2S, leave the area
immediately, utilizing an escape mask, if
provided. Evacuate upwind or crosswind and
report to a pre-determined safe area.
Make your emergency notification according to
your Emergency Action Plan. Details must be
given to ensure a timely response by EMS
personnel. If available, send someone out to
meet them and bring them into the site.
Yell “Man Down!!” sound the emergency alarm or whatever means has been
established at your worksite. Notify someone, such as a dispatcher or supervisor, of the
situation so emergency assistance can be made available.
It is important to remain as calm as possible so you can determine the number of
victims and to determine if any additional safety hazardous exist.
It is vital that you put on a breathing apparatus before attempting any rescue.
The oilfield is full of stories about workers being fatally injured trying to rescue coworkers without respiratory protection.