What has happened at Tianyuan Manganese Corp in northwest China’s Ningxia Hui at the end of the year 2010 has reminded me of the H2S hazard and the importance of the H2S monitor.
In that accident at work, according to the initial accident investigation, three people died which was caused by H2S gas poisoning. H2S was released when employees were mixing manganese carbonate and sulphuric acid at the plant site.
H2S or hydrogen sulfide has a specific odor like a rotten egg at the concentration of below 1 ppm in air. However, its odor can not be used as the H2S detection method. A reliable and continuous H2S monitor or H2S detection device is exactly required to avoid H2S poisoning.
Standards for H2S Exposure
H2S monitor or H2S detection relates closely with the concentration limit of H2S exposure. Various organizations have established standards for H2S exposure and understanding these standards is very critical in H2S monitor.
Here are some standards for H2S exposure in the workplace:
NIOSH IDLH or immediately dangerous to life or health: 100 ppm
OSHA PEL or permissible exposure limit for general industry (ceiling): 20 ppm
OSHA Maximum Peak: 50 ppm (10 minutes)
H2S Hazards Overview
H2S is colorless, toxic, and flammable with a strong rotten egg smell. It is also very important to understand H2S hazard exposure to you or your employees and plant facilities. The potential health hazard of H2S based on its concentration in the air is:
10-20 ppm: causes eye irritation
50-100 ppm: causes blurred vision and even eye damage, nose and throat irritation. Prolonged exposure may cause cough, runny nose, hoarseness, pneumonia, and breath shortness.
100-150 ppm: causes short-term smell loss.
200-250 ppm: causes severe irritation as well as symptoms like nausea, headache, vomiting, and dizziness. Prolonged exposure may cause lung damage or pulmonary edema. If the exposure time is 4-8 hours, H2S can cause death.
300-500 ppm: causes the same effects as in the concentration of 200-250 ppm but with sooner and more severe effects. Exposure time that can cause death is 1-4 hours.
500 ppm: causes excitement, dizziness, staggering, headache, unconsciousness, and respiratory failure in just 1 minute to 1 hour. Death can take place in 30 minutes to 1 hour in this condition.
Above 500 ppm: quickly causes unconsciousness and death.
H2S Detection Device Placement
Ideally, H2S monitor or H2S detection devices should be placed in the area where H2S gas release is routine or can be occurred accidentally. Besides, a portable H2S detection device is also required to measure H2S, for example in confined spaces.
H2S gas release problems are commonly found in crude oil storage tanks, oil and gas drilling sites, remote oil and gas well sites, H2S sludge dewatering, and chemical processing plant.
In conclusion, a good H2S monitor along with H2S leak control, ventilation equipment, and personal protective equipment (respirator) can prevent employees from H2S poisoning and plant facilities damage due to fire and explosion triggered by flammable H2S gas.