reply to post by Gold_Bug
It's true that toxic gases and voc's are being emitted from the blown out well and it is obvious that it is out of control. However, before jumping
the gun it sounds like Lindsay Williams was off by quite a bit with his figures. Lindsay was talking in "parts per billion" and all safety data is
given in parts per million. Take this example for Hydrogen Sulfide . The correct safety data is as follows:
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H2S Safety Factsheet
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August 2004
Hydrogen sulfide (H2S, CAS# 7783-06-4) is an extremely hazardous, toxic compound. It is a colourless, flammable gas that can be identified in
relatively low concentrations, by a characteristic rotten egg odor. The gas occurs naturally in coal pits, sulfur springs, gas wells, and as a product
of decaying sulfur-containing organic matter, particularly under low oxygen conditions. It is therefore commonly encountered in places such as sewers,
sewage treatment plants (H2S is often called sewer gas), manure stockpiles, mines, hot springs, and the holds of fishing ships. Industrial sources of
hydrogen sulfide include petroleum and natural gas extraction and refining, pulp and paper manufacturing, rayon textile production, leather tanning,
chemical manufacturing and waste disposal.
Hydrogen sulfide has a very low odor threshold, with its smell being easily perceptible at concentrations well below 1 part per million (ppm) in air.
The odor increases as the gas becomes more concentrated, with the strong rotten egg smell recognisable up to 30 ppm. Above this level, the gas is
reported to have a sickeningly sweet odor up to around 100 ppm. However, at concentrations above 100 ppm, a person's ability to detect the gas is
affected by rapid temporary paralysis of the olfactory nerves in the nose, leading to a loss of the sense of smell. This means that the gas can be
present at dangerously high concentrations, with no perceivable odor. Prolonged exposure to lower concentrations can also result in similar effects of
olfactory fatigue. This unusual property of hydrogen sulfide makes it extremely dangerous to rely totally on the sense of smell to warn of the
presence of the gas.
Health Effects of Hydrogen Sulfide
H2S is classed as a chemical asphyxiant, similar to carbon monoxide and cyanide gases. It inhibits cellular respiration and uptake of oxygen, causing
biochemical suffocation. Typical exposure symptoms include:
LOW
0 - 10 ppm Irritation of the eyes, nose and throat
MOD
10 - 50 ppm Headache
Dizziness
Nausea and vomiting
Coughing and breathing difficulty
High
50 - 200 ppm Severe respratory tract irritation
Eye irritation / acute conjunctivitis
Shock
Convulsions
Coma
Death in severe cases
Prolonged exposures at lower levels can lead to bronchitis, pneumonia, migraine headaches, pulmonary edema, and loss of motor coordination.
Working with Hydrogen Sulfide
Most countries have legal limits in force that govern the maximum allowable levels of exposure to hydrogen sulfide in the working environment. A
typical permissible exposure limit in many countries is 10 ppm. While the distinctive odor of H2S is easily detected, its olfactory fatigue effects
mean that one cannot rely on the nose as a warning device. The only reliable way to determine exposure levels is to measure the amount in the air.
Regular monitoring will help to identify areas and operations likely to exceed permissible exposure limits, and any areas that routinely pose
overexposure hazards should be equipped with continuous monitoring systems.