- Enter the IMCA Awards 2024: We\'re looking for outstanding Safety, Sustainability, and GHG projects.
- IP Code: Mandatory Code enters into force on 1 July. Make sure your company is up to speed with the changes.
- Early Bird tickets available for the IMCA Global Summit 2024. 3-4 December, Utrecht, Netherlands. Members can save £400.
- Discover how we are helping Members reduce emissions: Explore the ProjectGHG hub now.
- Now booking. Join the Lifting and Rigging community at our Technical Seminar in Amsterdam. Thursday 12 September 2024
- Now booking. Underwater Ship Husbandry Seminar. 10 October 2024, Singapore.
Bell contamination
A member has reported that during a recent diving project, a subsea fitting failure caused divers to become contaminated with a hazardous substance released from a hose under pressure. Diver 1 subsequently returned to the bell and entered the bell and was allowed to enter without taking the necessary precautions to ensure that he was free from contamination. On removal of his diving helmet, he reported to the bellman that he felt faint. The diver was put on to the built-in breathing system (BIBS) and the bell was flushed through. Decontamination measures were then taken and diver 2 was subsequently recovered to the bell. During this incident a Hyper-Gas II analyser situated in the bell did not alarm and the bellman said he was unaffected.
A review of the incident was carried out by the member company, noting the following points:
- The analyser in use was an infra-red analyser that looks at the specific band of light related to crude oil and condensate and cannot necessarily be relied upon when vapour from only one or two specific hydrocarbons are present, as these may fall outside the band of infra red light being analysed;
- Where the analyser is to be used in an environment where vapour from other hydrocarbons could be present, it may be advisable to reset the analyser specifically to respond to these hydrocarbons;
- While the Hyper-Gas II analyser is capable of seeing specific fractions of hydrocarbons as part of crude or condensate mix, such fractions need to be at a relatively high concentration before the unit will alarm, e.g. 10% of the anaesthetic requirement. Concentrations of other chemical substances may also be at levels well above the occupational exposure standard (OES) and be well on the way to a level that will incapacitate the bell occupants, with potentially fatal consequences, before an alarm is given;
- The levels of individual hydrocarbons which cause anaesthesia are several orders of magnitude higher than the allowed occupational exposure standard for each compound. This being so the Hyper-Gas II cannot be, and has never been presented as, a first line warning of hydrocarbon contamination in the bell;
- Human sensory awareness can, in some circumstances, detect (but not quantify) substances before electronic devices. However, this must never be relied upon as a means of detection;
- Although the bell is small, contamination may occur in one area of the bell but not in others. This will depend on gas flows within the bell, composition/molecular weight of the contaminant chemicals and also how the contaminant is introduced into the bell, e.g. by the umbilical, contaminated clothing or gaseous ingress into the bell trunk. In two- and three-man bells mixing would naturally occur due to the restricted volume.
Members are reminded of the following:
- Analysers can usually only warn of an event once it is occurring and they should not be relied upon as the primary warning of bell contamination. Prevention of contamination and the use of enhanced diving techniques should be the primary defence against bell contamination;
- Where contamination is possible, enhanced diving procedures should be used. These include: correct bell positioning, the use of BIBS by the bellman prior to diver recovery and prior to assisting the diver when contamination is suspected, decontamination of umbilical, removal of protective coveralls and thorough diver decontamination prior to bell entry, testing of the bell atmosphere using the appropriate Draeger tubes to confirm bell conditions;
- At the planning stage of an operation, the project engineer should ensure any chemicals/hazardous substance used during the operation, or contained within the system to be worked on, are identified and a material safety data sheet (MSDS) is obtained;
- The MSDS for each substance should be presented to the project safety adviser, who will arrange for a safety assessment to be completed, including a diving assessment;
- A review of the chemical/hazardous substance will consider the need for any additional specific Draeger tubes to identify contamination/quantify bell atmospheric conditions.
A video showing the effects of an anaesthetic chemical within a contaminated bell is available from Analox.
Safety Event
Published: 20 December 2007
Download: IMCA SF 10/07
IMCA Safety Flashes
Submit a Report
IMCA Safety Flashes summarise key safety matters and incidents, allowing lessons to be more easily learnt for the benefit of all. The effectiveness of the IMCA Safety Flash system depends on Members sharing information and so avoiding repeat incidents. Please consider adding [email protected] to your internal distribution list for safety alerts or manually submitting information on incidents you consider may be relevant. All information is anonymised or sanitised, as appropriate.
IMCA’s store terms and conditions (https://www.imca-int.com/legal-notices/terms/) apply to all downloads from IMCA’s website, including this document.
IMCA makes every effort to ensure the accuracy and reliability of the data contained in the documents it publishes, but IMCA shall not be liable for any guidance and/or recommendation and/or statement herein contained. The information contained in this document does not fulfil or replace any individual’s or Member's legal, regulatory or other duties or obligations in respect of their operations. Individuals and Members remain solely responsible for the safe, lawful and proper conduct of their operations.