Last week we reported on the fact-finding meeting on slurry gas and its dangers held recently in Northern Ireland (NI). It also discussed the promising safety benefits of aeration systems.
Pumping low volumes of air into a slatted tank for a few hours every day can result in the poisonous hydrogen sulphide (H2S) gas being released at relatively low levels, which can safely disperse. This contrasts with the deadly surge of this invisible gas that follows mechanical agitation of crusted slurry. The organisers of the meeting, members of the NI branch of the Institution of Agricultural Engineers, have now drawn up a number of challenges aimed at tackling the dangers of handling slurry. For example, they ask if aeration systems can be developed for retro-fitting in existing tanks at reasonable cost without a need to empty out the tanks.
They recommend greater levels of ventilation at floor level in sheds – if doors won’t provide it then possibly through use of fans. They recommend that safety be given greater priority in design of new sheds, if not by use of tank aeration then by moving slurry storage outside the shed where H2S will disperse more quickly, especially in breeze.
Low-rate aeration
In joint research, AFBI and Grange examined the effectiveness of aeration in reducing the dangers of slurry gas release in slatted tanks. Aerator systems work by injecting low volume and low-pressure air into the base of slurry tanks through carefully located pipes and aeration nozzles. The results showed that:
H2S is released only when aerators are running (three to seven hours per day) One farm reached peak production of 119ppm but only for a short period. 10ppm was reached on every farm but for very short periods of 10 minutes per day. These figures are all for measurements just below slat level – and are likely to be reduced by dilution with clean air within the house itself. While not conclusive, these results suggest that low-rate aeration has the potential to aid slurry management without producing dangerous levels of hydrogen sulphide above slat level.
Grange tanks
Non-aerated slurry tanks required mixing before removal of slurry. There was considerable variation in slurry dry matter and two of the tanks required water addition during mixing. The maximum level of H2S recorded during mixing was 257ppm. The maximum level of H2S recorded during pumping was 107ppm.
In contrast, aerated tanks could be pumped without mixing. The slurry was of consistent DM.
There were very low H2S levels recorded throughout the housing period. H2S was detected in less than 1% of readings. The maximum level recorded was 7ppm. The maximum level at the reception point during pumping was 30ppm and 99% of readings were below 5ppm
No significant difference was detected in nutrient content between aerated and non-aerated.
Conclusions
Slurry stored with low rate, intermittent aeration:
Was effectively mixed. Released very low levels of H2S. Had a nutrient concentration which was not significantly different from slurry from conventional storage. Challenges
The organisers of the meeting have now drawn up a number of challenges aimed at tackling the dangers of handling slurry
Education and Guidance
Communication
To deliver communication of a clear unequivocal message effectively to those people mixing and working with slurry.
The message must be simple, innovative and professional, making effective use of social media and other cost-effective methods. It must be realistic and aimed at reducing risk to acceptably safe levels, rather than eliminating it entirely.
Monitors
To produce clear guidance on the ways in which monitors can be used to enhance safety.
Recent technical developments mean current advice should be reviewed.
Face masks and
emergency hoods
To produce clear guidance on the selection and use of face masks and emergency hoods during slurry mixing operations and emergency situations.
Again, improved design, availability and low cost of these items need to be taken into account. Lack of suitable realistic guidance is impeding progress.
Course content and
availability
Review the content of education programmes – not just safety courses – to ensure that the safe handling of slurry is adequately addressed.
Training needs to be provided by suppliers and/or educators on the use of monitor alarms, face masks and emergency hoods.
Research
Provide funding for work on low-volume aeration systems.
Research at AFBI and Teagasc strongly suggests such systems offer high levels of safety as well as management advantages. The existing work needs to be validated and extended to provide confirmation and confidence in a wider range of situations and establish design parameters for the equipment.
Overall the funding invested in research on the topic of slurry gas on farms and the promotion of safe systems of work needs to be increased.
Engineering
Design of new livestock housing
Ensure that high levels of ventilation at slat level are provided over all slatted tanks. Thorough ventilation at slat level must be provided in all houses – if this cannot be done through large doors at each end then fans should be used, eg the T Mac-Safeair unit.
Ensure that safe slurry systems are an inherent primary element of the design brief for all livestock housing. The institution questions whether simple, deep, slatted tanks, even with outside mixing points, can in many cases provide a sufficient degree of safety.
Either scraping into external stores or using bubbler systems in tanks beneath slats should become the design norm. Increasingly, systems need to be capable of safe slurry mixing and removal in situations where stock are housed all year.
Retrofitting intermittent low-volume aeration
Stimulate development of intermittent low-volume aeration (bubbler) systems which can be installed from the top into existing tanks.
Many deep tanks exist without outside mixing points. Modification to allow outside mixing can be expensive and requires complete emptying of the tanks. Current bubbler systems also require tanks to be completely emptied for safe and effective installation. The ability to retrofit bubbler systems without having to empty tanks and remove slats would be a major advantage.
Robots and remote
working
Stimulate the application of cost-effective robotic systems for mixing slurry and monitoring gas levels in houses during mixing.
Panel discussion
The following points arose during the panel discussion from speakers and delegates
The use of half face masks is not as simple as it may seem at first. Their use needs good training and management. Also, users must be clean shaven to prevent potentially dangerous leakage. Advice will always have to overcome the psychological makeup of humans and especially farmers who are predisposed to ignore or underestimate risk. The unpredictability and years of “never having a problem” make this particularly difficult for slurry gases. Legislation will be ineffective as it cannot be rigorously enforced; but the influence of wives, partners and children must be effectively utilised. Practical suggestions made included having a safe system of handling slurry incorporated as a requirement for quality assurance schemes and making warning signs mandatory at every slatted house and mixing point. Figures confirm that one of the principal danger points is when the pump operator checks on mixing inside the house. The new T Mac-Safeair-Unit fan, linked to jetter direction is intended to reduce gas levels in this area. There is no evidence that introducing “bugs” or enzymes into slurry reduces H2S production. Manufacturers are careful not to claim that they do so – only suggesting that they have the potential to do so. The mechanism cannot introduce oxygen to prevent the redox process which ultimately leads to H2S production. Anecdotal evidence does suggest that they may help reduce crusting and lead to a more easily mixed product which will reduce the need for vigorous mixing. Use of personal hydrogen sulphide monitors should be encouraged as an addition to safe systems of work. These units have now become much cheaper and easier to use and maintain. The Sundstrom Escape Hood or other equivalent devices appear to offer potential and should be considered.
Last week we reported on the fact-finding meeting on slurry gas and its dangers held recently in Northern Ireland (NI). It also discussed the promising safety benefits of aeration systems.
Pumping low volumes of air into a slatted tank for a few hours every day can result in the poisonous hydrogen sulphide (H2S) gas being released at relatively low levels, which can safely disperse. This contrasts with the deadly surge of this invisible gas that follows mechanical agitation of crusted slurry. The organisers of the meeting, members of the NI branch of the Institution of Agricultural Engineers, have now drawn up a number of challenges aimed at tackling the dangers of handling slurry. For example, they ask if aeration systems can be developed for retro-fitting in existing tanks at reasonable cost without a need to empty out the tanks.
They recommend greater levels of ventilation at floor level in sheds – if doors won’t provide it then possibly through use of fans. They recommend that safety be given greater priority in design of new sheds, if not by use of tank aeration then by moving slurry storage outside the shed where H2S will disperse more quickly, especially in breeze.
Low-rate aeration
In joint research, AFBI and Grange examined the effectiveness of aeration in reducing the dangers of slurry gas release in slatted tanks. Aerator systems work by injecting low volume and low-pressure air into the base of slurry tanks through carefully located pipes and aeration nozzles. The results showed that:
H2S is released only when aerators are running (three to seven hours per day) One farm reached peak production of 119ppm but only for a short period. 10ppm was reached on every farm but for very short periods of 10 minutes per day. These figures are all for measurements just below slat level – and are likely to be reduced by dilution with clean air within the house itself. While not conclusive, these results suggest that low-rate aeration has the potential to aid slurry management without producing dangerous levels of hydrogen sulphide above slat level.
Grange tanks
Non-aerated slurry tanks required mixing before removal of slurry. There was considerable variation in slurry dry matter and two of the tanks required water addition during mixing. The maximum level of H2S recorded during mixing was 257ppm. The maximum level of H2S recorded during pumping was 107ppm.
In contrast, aerated tanks could be pumped without mixing. The slurry was of consistent DM.
There were very low H2S levels recorded throughout the housing period. H2S was detected in less than 1% of readings. The maximum level recorded was 7ppm. The maximum level at the reception point during pumping was 30ppm and 99% of readings were below 5ppm
No significant difference was detected in nutrient content between aerated and non-aerated.
Conclusions
Slurry stored with low rate, intermittent aeration:
Was effectively mixed. Released very low levels of H2S. Had a nutrient concentration which was not significantly different from slurry from conventional storage. Challenges
The organisers of the meeting have now drawn up a number of challenges aimed at tackling the dangers of handling slurry
Education and Guidance
Communication
To deliver communication of a clear unequivocal message effectively to those people mixing and working with slurry.
The message must be simple, innovative and professional, making effective use of social media and other cost-effective methods. It must be realistic and aimed at reducing risk to acceptably safe levels, rather than eliminating it entirely.
Monitors
To produce clear guidance on the ways in which monitors can be used to enhance safety.
Recent technical developments mean current advice should be reviewed.
Face masks and
emergency hoods
To produce clear guidance on the selection and use of face masks and emergency hoods during slurry mixing operations and emergency situations.
Again, improved design, availability and low cost of these items need to be taken into account. Lack of suitable realistic guidance is impeding progress.
Course content and
availability
Review the content of education programmes – not just safety courses – to ensure that the safe handling of slurry is adequately addressed.
Training needs to be provided by suppliers and/or educators on the use of monitor alarms, face masks and emergency hoods.
Research
Provide funding for work on low-volume aeration systems.
Research at AFBI and Teagasc strongly suggests such systems offer high levels of safety as well as management advantages. The existing work needs to be validated and extended to provide confirmation and confidence in a wider range of situations and establish design parameters for the equipment.
Overall the funding invested in research on the topic of slurry gas on farms and the promotion of safe systems of work needs to be increased.
Engineering
Design of new livestock housing
Ensure that high levels of ventilation at slat level are provided over all slatted tanks. Thorough ventilation at slat level must be provided in all houses – if this cannot be done through large doors at each end then fans should be used, eg the T Mac-Safeair unit.
Ensure that safe slurry systems are an inherent primary element of the design brief for all livestock housing. The institution questions whether simple, deep, slatted tanks, even with outside mixing points, can in many cases provide a sufficient degree of safety.
Either scraping into external stores or using bubbler systems in tanks beneath slats should become the design norm. Increasingly, systems need to be capable of safe slurry mixing and removal in situations where stock are housed all year.
Retrofitting intermittent low-volume aeration
Stimulate development of intermittent low-volume aeration (bubbler) systems which can be installed from the top into existing tanks.
Many deep tanks exist without outside mixing points. Modification to allow outside mixing can be expensive and requires complete emptying of the tanks. Current bubbler systems also require tanks to be completely emptied for safe and effective installation. The ability to retrofit bubbler systems without having to empty tanks and remove slats would be a major advantage.
Robots and remote
working
Stimulate the application of cost-effective robotic systems for mixing slurry and monitoring gas levels in houses during mixing.
Panel discussion
The following points arose during the panel discussion from speakers and delegates
The use of half face masks is not as simple as it may seem at first. Their use needs good training and management. Also, users must be clean shaven to prevent potentially dangerous leakage. Advice will always have to overcome the psychological makeup of humans and especially farmers who are predisposed to ignore or underestimate risk. The unpredictability and years of “never having a problem” make this particularly difficult for slurry gases. Legislation will be ineffective as it cannot be rigorously enforced; but the influence of wives, partners and children must be effectively utilised. Practical suggestions made included having a safe system of handling slurry incorporated as a requirement for quality assurance schemes and making warning signs mandatory at every slatted house and mixing point. Figures confirm that one of the principal danger points is when the pump operator checks on mixing inside the house. The new T Mac-Safeair-Unit fan, linked to jetter direction is intended to reduce gas levels in this area. There is no evidence that introducing “bugs” or enzymes into slurry reduces H2S production. Manufacturers are careful not to claim that they do so – only suggesting that they have the potential to do so. The mechanism cannot introduce oxygen to prevent the redox process which ultimately leads to H2S production. Anecdotal evidence does suggest that they may help reduce crusting and lead to a more easily mixed product which will reduce the need for vigorous mixing. Use of personal hydrogen sulphide monitors should be encouraged as an addition to safe systems of work. These units have now become much cheaper and easier to use and maintain. The Sundstrom Escape Hood or other equivalent devices appear to offer potential and should be considered. 
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