Diver safety
The Analox Hyper-Gas MII™ is designed to detect and warn divers of, potentially fatal, anaesthetic levels of hydrocarbons in the diving bell. Where divers are working on dirty sites, there is a likelihood for contamination of the bell atmosphere from vapourisation of contaminants carried on dive suits and umbilical lines, even when divers are wearing additional safety dive suits. Vapourisation of hydrocarbons into the bell can occur within minutes and can rapidly rise to anaesthetic concentrations.
Real dangers to divers
In the presence of anaesthetic levels of volatiles divers can suffer the effects within a few breaths. Even before unconsciousness, the ability to react normally becomes impaired. The effects caused by sub anaesthetic levels can be compared with the pattern of behaviour caused by alcohol consumption. The following effects have been detailed by Fang et al. (1996);
33% of the anaesthetic level of toluene leads to hyperactivity.
13% of the anaesthetic level of xylene causes tremors which could impair purposeful actions.
44% of the anaesthetic level of benzene causes uncontrolled jerking of limbs.
52% of the anaesthetic level of cyclo-hexane causes convulsions.
How it works
The Hyper-Gas MKII™ comprises;
Bell monitor; once mounted inside the bell, the monitor will rapidly detect the presence of vapourised hydrocarbons, and will activate audible and visual alarms before the anaesthetic threshold is reached.
Topside repeater, mounted at the surface the topside repeater mimics the conditions inside the bell.
Technology
The Analox Hyper-Gas MK II™ system has been designed to operate to depths up to 60 Bar A. It uses a unique hyperbaric hydrocarbon sensor based on highly respected Analox infra red technology. The sensor is sensitive to a range of hydrocarbons, and is able to detect all those commonly given off by the vapourisation of crude oil or condensate.
Topside engineer checking topside repeater unit Automatic correction of pressure and temperature effects ensures the analyser will offer optimum performance in this difficult environment.
Gas alarm
The gas alarm level is preset to 10% of the anaesthetic dose of vapourised hydrocarbons that could be present in the diving bell. The sensor gives an additive response to the range of hydrocarbons normally present, not one individual compound. For diving in areas where contamination is known to be from 1 or 2 compounds, an alternative alarm set point could be calculated by Analox
Response time
The sensor needs to be mounted within the diving bell, rather than relying on an umbilical fed analyser because anaesthesia, or the effects of sub anaesthetic levels can occur within a few breaths, i.e. a few seconds. By analysing for hydrocarbons at the surface its likely that the effects would occur before an alarm is raised. A rapid response is crucial. The Hyper-Gas MKII™ has been designed with an internal sample pump to ensure a fast response to hydrocarbons.
Datalogging
The Hyper-Gas MKII™ system is fitted with a factory set datalogging facility. This logs and measured levels of hydrocarbons, the depth and the corresponding data and time. Once the datalogging capacity is exceeded the Hyper-Gas MKII™ will automatically overwrite the oldest data. Data can be downloaded via the topside repeater or bell monitor onto a PC, using the data communications cable, and the datalog retrieval programme.