Know your limits, and the limits of your equipment, and know what your detector is detecting are a couple of the lessons learned from a close-call incident during a Port State Control Certificate of Compliance “Gas”, COC-Gas, exam involving entry into a cargo compressor room aboard an LPG carrier. The vessel’s fixed gas detectors did not set off an alert even though the atmosphere was hazardous.
Says USCG Sector Houston – Galveston: ” personnel recently averted a potentially hazardous exposure to 1,3 butadiene, a known carcinogen, while conducting a Port State Control Certificate of Compliance “Gas” (COC-Gas) exam. The examiners followed USCG Sector Houston-Galveston guidance for entry into cargo compressor rooms that required the space to be certified “Safe for Workers” by a marine chemist prior to entry of Coast Guard personnel. With the compressors secured and ventilation in operation the Marine Chemist found 35 ppm of 1,3 butadiene within the compressor room and could not certify the space as safe for workers in accordance with the published NIOSH Short Term Exposure Limit, STEL, of 5 ppm.
“When notified of the gas in the compressor room the inspection team discussed their concem with why the fixed gas detection system was not identifying the presence of the gas. Further research determined that the lower explosive limit (LEL) for 1,3 butadiene is 20,000 ppm, and the fixed gas detection alarm set point of 10% of LEL would be 2,000 ppm. The 35 ppm reading obtained on the marine chemist’s photo-ionization detector (PHD) would correlate to approx .00175 % LEL, a level not measurable on the fixed gas detection system. Failure to follow this local guidance would have resulted in persormel being exposed to seven times the maximum limit allowed by the STEL”.
So, although the atmosphere was ‘safe’ with regard to the hazard of exposure it was not safe with regard to health.
Concludes the USCG: “All persormel working around 1,3 Butadiene should be keenly aware of and cautious of gas leaks and review MSDS for specific hazards and exposure limits. It is critical to understand the different hazards associated with all gaseous cargoes and the limitations of the meters in use on board and carried. Failure to follow written procedures or take appropriate precautions prior to entering or working in an area suspected of or likely to contain even the slightest amount of cargo vapor may result in long term health issues.