Hydrogen Sulfide Gas (H2S)

How fast can H2S kill you?

Is H2S harmful to humans?

why excavations deeper than 4 ft. require gas testing

What does H2S gas do to the human body?

Is H2S is flammable?

hydrogen sulfide

H2S causes the most common aund the largest number of deaths in the oil and gas industry worldwide

Hydrogen sulfide is highly toxic and colourless—you cannot see the gas in the atmosphere.

More than its flammability, its greatest danger for humans is its high toxicity. By the time flammable concentrations are reached, its toxic hazard will kill you in one breath.

How fast can H2S kill you?

H2S kills your sense of smell if you are exposed to it for a length of time and more quickly at higher concentrations. The only safe way to detect hydrogen sulfide is by using a calibrated gas monitor. Always carry a gas monitor when you enter an area where H2S may be present.

A single breath of H2S can damage the respiratory control centre. Because H2S leaks cannot be seen, H2S has killed many people who enter areas they thought looked safe.

When inhaled it goes from the lungs into the bloodstream immediately, where it can rapidly paralyze the breathing control centre in the brain and cause the lungs to cease functioning, with death from suffocation within minutes.

h2s NFPA chart

Note - above chart fault correction Vale (read value)

Never trust your sense of smell to detect h2s! If you smell H2S and it goes away, it does not mean all is fine. It probably got worse! At very low concentrations h2s smells like rotten eggs (OSHA). But you cannot smell it at higher concentrations and/or longer exposures. Consequently, the sense of smell does not give you enough warning of hazardous concentrations.

10 PPM. Between 10 – 100 PPM, you must wear SCBA. Above 100 PPM no work or confined space entry is allowed.

H2S exposure limit
NEOSH	REL	TWA	10 ppm
		STEL	15 ppm
		IDLH	100 ppm
OSHA	PEL	TWA	10 ppm
		STEL	15 ppm
		IDLH	100 ppm
ACGIH	TLV	TWA	1 ppm
		STEL	5 ppm
		IDLH

why excavations deeper than 4 ft. require gas testing?

H2S is heavier than air and tends to sink into low-lying (below ground) areas, such as pipeline trenches, valve boxes, sumps, sewers, excavations, and low areas around rig platforms.

That is why excavations deeper than 4 ft. require gas testing and a confined space entry permit regardless of where they are located.

Is H2S is flammable?

Besides being highly toxic, H2S is extremely flammable and explosive over a wide range of concentrations in the air. The gas will catch fire at the right concentration with oxygen.

The lower explosive limit (LEL) is 4.3% and the upper explosive limit (UEL) is 46%. That is 43000 ppm and 460000 ppm respectively and will certainly kill you dead in one breath, but it can also pose an explosion hazard at these concentrations.

Is H2S harmful to humans?
What does H2S gas do to the human body?

Even at relatively low concentrations, H2S is toxic and its concentration in air is measured in parts per million (ppm).

Continuous sensing detectors must be regularly checked, maintained, and calibrated or they may fail to alarm when an H2S release occurs.

Hazards: High concentration,

• Shock
• Convulsion
• Unable to breath
• Coma
• Death

H2S Effect on human body
0.01 – 1.5 ppm	Odour threshold
2 – 5 ppm	Headache, nausea, eye irritation
20 ppm	Poor memory, dizziness
30 ppm	Loss of smell, injury to olfactory gland
100 ppm	Respiratory system pyrolysis
200 ppm	Permanent eye nerves damage
300 ppm	Loss of sense
500 ppm	Asphyxia
700 ppm	Breathing will stop
1000 ppm	Death within a minute

Safety measure: 

• Gas test - air need to be tested

• Ventilation - gas is present the should be ventilated

• If the gas can not remove, use respiratory protection

• Avoid low-lying area

• observe signage of H2S

• Observe alarm

• Check crosswind direction

• Know the assembly area

• Know the eyewash station

• Know the manual call point

• Know the emergency contact number

first-aid and rescue:

• Keep calm, don't be panic

• Rescue by only trained people

• Wear breathing apparatus

• Take the victim to fresh air

• Give artificial respiration if the victim is unresponsive

• Take to hospital

Abbreviations

PEL - Permissible exposure limit

REL - recommended exposure limit

TLV - threshold limit value

PPM - Parts per million (1 ppm = 1.40 mg/m3)

IDLH - immediately dangerous to life and health(no entry)

TWA - time-weighted average (8 hours)

STEL - short term exposure limit (15 minutes)