Technical article on occupational health and safety silo cleaning

Technical article on occupational health and safety silo cleaning

Occupational safety in silo cleaning and silo access technology

Silo systems, shafts and tank systems in the industrial and agricultural sectors must be entered by people for inspection and cleaning purposes. From the point of view of the German Social Accident Insurance and the employers’ liability insurance associations, these inspections fall under “confined space”, i.e. containers, silos and confined spaces.

Part 1: Working in containers, silos and confined spaces.

DGUV Rule 113-004. 113-004.

DGUV rules also show ways of preventing accidents at work, occupational illnesses and work-related health hazards where there are no occupational health and safety or accident prevention regulations. They also pool the knowledge gained from the prevention work of the accident insurance institutions.

Containers and confined spaces are areas surrounded on all sides or predominantly by solid walls in which, due to their spatial narrowness, insufficient air exchange or the substances, mixtures, impurities or equipment located or introduced in them, special hazards exist or can arise that go well beyond the potential hazards normally found in workplaces.

Areas that are only partially surrounded by solid walls, but in which hazardous substances can accumulate or a lack of oxygen can occur due to local conditions or the design, are also confined spaces within the meaning of this rule. No arbitrary measures!

Confined spaces and containers

If the occurrence of particular hazards (see below) cannot be ruled out with certainty, confined spaces, for example, are also to be regarded as confined spaces:

  • Tank cups
  • Pits
  • manholes
  • canals
  • Ship holds
  • Weighing pits
  • Cavities in buildings and machines
  • Box girders of bridges and cranes
  • Hubs, rotor blades and spinners of wind turbines


In its regulations, the German Social Accident Insurance specifies rules and regulations that are intended to make it safe to enter rooms with an increased risk of accidents. Nevertheless, being in such areas is associated with many hazards, which we would like to highlight in detail.

Particular hazards from substances or mixtures can exist or arise in confined spaces and containers

  • through work processes, e.g. welding, grinding, cleaning with liquids or solids,
  • through surface treatment,
  • through stirring up residues,
  • through biological processes, e.g. fermentation, putrefaction,
  • through chemical reactions,
  • through gases used for flushing,
  • through substances and mixtures that can penetrate through leaky linings or leaky shut-off devices,
  • through oxygen deficiency; this can occur due to inert gases used for flushing or due to substances (including container material) that absorb, chemically or physically bind or displace oxygen (see also Annex 5); oxygen consumption at work, unsuitable and inadequate ventilation when working in containers, silos or confined spaces can also lead to oxygen deficiency,
  • through oxygen enrichment; e.g. B. through incorrect operation or leaks during welding work,
  • through hot substances or mixtures, bulk goods, liquids or flowable substances and mixtures that are present in containers or narrow spaces or that penetrate into them,
  • through the removal of caking,
  • through gases, vapors, mists or dusts that can cause fires or explosions.
  • Particular hazards from equipment can exist, for example, in containers, silos and narrow spaces or arise from
  • moving parts or fittings, such as mixing, crushing, loosening, conveying or ventilation equipment,
  • heated or cooled container parts and fittings,
  • closing or opening valves in lines or ducts, e.g. B. Slide valves, flaps, explosion-proof decoupling devices,
  • operating under electrical voltage
  • Access procedures:
  • Access procedures are work procedures that enable access to the container, silo or confined space (usually with the aid of work equipment). Such procedures can be:
  • Easy entry without aids (usually for access points that are located below)
  • Access using ladders (permanently installed ladders or mobile ladders)
  • Access using hoistable personal access equipment in accordance with DGUV Rule 101-005 “Hoistable personal access equipment”
  • Access using a safety harness as a body restraint and a winch for transporting people
  • Positioning procedures within the meaning of this DGUV Rule are work procedures in which people are positioned at a specific point in the container, silo or confined space in order to carry out work. They remain in the personal access equipment. For positioning, hoistable personnel lifting devices in accordance with DGUV Rule 101-005 “Hoistable personnel lifting devices” or rope-assisted access and positioning procedures (SZP) in accordance with TRBS 2121 Part 3 and DGUV Information 212-001 “Working using rope-assisted access and positioning procedures” can be used.
  • Access / access openings
  • Access to containers and confined spaces can be, for example:
  • Doors
  • Entrances
  • Manholes
  • Folding ladders
  • Climbing iron walkways

Free measurement / redundancy measurements

Clearance measurement is the determination of a possible concentration of hazardous substances or the oxygen content with the aim of establishing whether the atmosphere in the container, silo or confined space allows safe working.

Clearance measurements are not measurements within the meaning of the Hazardous Substances Ordinance or the Technical Rules for Hazardous Substances “Determination and Assessment of the Concentration of Hazardous Substances in Work Areas” (TRGS 402).

Redundancy measurements are multiple cross-system measurements by different device manufacturers. In the event of an increased risk situation, measurements are carried out with redundancy in the risk analysis. This clearly and unambiguously prevents any incorrect measurements that may occur.


The supervisor is a person appointed by the contractor who is responsible for supervising the preparation and execution of work in containers, silos and confined spaces. The qualifications of the supervisor must correspond to SZP rope access positioning level 3.

The content of such qualifications includes rescue and first aid dynamics, as well as all occupational health and safety preparatory measures. A trained safety specialist with a FISAT supervisor qualification would therefore be an excellent supervisor qualification. In our company, the business owners provide this position for every assignment, thus guaranteeing an unlimited safe execution of the order.

Influence of leadership behavior

Managers have a key influence on maintaining and promoting the mental health of their employees. Numerous empirical studies have shown positive correlations between leadership and employee health.

For example, studies in which managers were transferred from departments with high absenteeism to departments with low absenteeism showed that the absenteeism rate increased significantly as a result. High absenteeism can be an expression of “silent employee protest”, one possible cause of which is experienced stress. According to research findings, employee- and participation-oriented management styles have the effect of reducing stress and absenteeism; in contrast, an authoritarian management style, i.e. a management style that is only task-oriented and does not take employee participation into account, leads to an increase in absenteeism.

Organizations with an employee- and participation-oriented management style also plan health programmes more frequently, for example.

Employee-oriented management of employees

Constructive working relationships are established and developed through a democratic, employee- and participation-oriented management style. Important management techniques in terms of a mutually satisfactory working relationship include: selecting the right employee for the right job; allowing sufficient time for new employees or new tasks to be trained; counteracting excessive demands and underchallenges; taking employees’ personal career goals into account; highlighting development opportunities; agreeing specific, realistic work goals; providing feedback on work results in personal discussions; recognizing positive performance; communicating regularly with employees; keeping employees fully informed about operational issues and changes; creating a climate of trust; promoting cohesion in the work group; conveying a sense of appreciation.

Security posts

A safety guard is a person who maintains constant contact with the people working in the container, silo or confined space and, if necessary, carries out or initiates rescue measures. This is an access technician with rescue qualifications and first aider training. Physical fitness and reliability are important criteria for this position.

Risk assessment

Before starting work, the contractor must carry out a risk assessment. If hazards are identified, organizational measures must be taken to minimize the risk potential / hazard potential.

The specified measures must be recorded in a permit / safety assessment or in operating instructions.

The preparation of the permit based on the sample permit of this rule specifies the general catalog of hazards for the respective situations in the company. The carefully and comprehensively prepared permit is the basis for the risk assessment in the specific case.

Safety assessment

The security assessment complements the access documentation preparation and makes a significant contribution to the security of the documentation. In the security assessment, the plant operator and the executing companies are considered equal and their respective responsibilities are set out in writing. Since certain plant specifications are made by the plant operator on their own responsibility, they also contribute to the obligation to communicate/transfer information. The security assessment therefore represents elements that enable a secure access solution.

The contents of a safety assessment are: system specifications / system drawings, system manager, security and access elements, operator information and guidelines, work location markings and definition of rights and obligations, special markings and special regulations to supplement occupational health and safety, safety data sheets for the expected substances, ATEX documentation, access solutions, positioning procedures, rescue planning and dynamics, functional routes and reporting devices, radio connection data, radio managers and radio structure, indirect and immediate hazards, crisis behavior and solution concepts, process routes and mapping procedure, work process organization, work sketches, tool box talk, last minute sheet, responsible persons, external gas measurements and results, redundancy protection, access times and deployment times, equipment positioning, fire and permit certificates, deployment and use of industrial trucks, protocol for securing pressure-operated doors, recording of weather conditions.

The supervisor is responsible for maintaining and updating the safety assessment.

Lifting of the protective measures

The system operator or owner and their authorized representative may not remove any protective measures or interfere with the safety procedures of the supervisor in any other way. The supervisor bears direct responsibility for his personnel. Protective measures may only be lifted by the supervisor once the work has been completed and all persons have left the containers, silos and confined spaces.

Lastminute sheet

The last-minute sheet is a protocol which is completed and signed by the team members as the last control segment. This protocol lists the criteria that are used for the final check of the belay route. Anchor devices, rope cut, rope type, selection of special equipment by the access technician, equipment detail check, marking of anchor points, securing and evaluation, rope protection evaluation, redundancy evaluation, rope protection marking.

Separation of containers, silos and confined spaces

Before starting work in containers, silos and confined spaces, the supervisor must ensure that all entrances and exits to the containers, silos and confined spaces through which hazardous substances or asphyxiating gases can enter containers, silos and confined spaces in dangerous concentrations or quantities or at dangerous temperatures or pressures are effectively blocked. The plant operator or his authorised representative is liable for the implementation of the separation by signing the safety assessment. In practice, the physical and structural separation is carried out in the presence of the supervisor.

Inlets and exits for substances can, for example, be: B. can be effectively interrupted by the following measures: by removing intermediate pieces, separating flange connections and blind flanges of the openings, by two shut-off devices arranged one behind the other, if a suitable connection to the outside air (intermediate relief) is established between these, the operating devices are secured against unintentional, unauthorised or erroneous opening and the intermediate relief has been checked for its effectiveness, by tightly closing, clearly identifiable blanking plates, if the dimensions and material are adapted to the temperatures, material stresses and pressures occurring, by two shut-off devices arranged one behind the other without intermediate relief, if no pressure build-up is possible upstream of the shut-off devices and the operating devices are secured against unintentional, unauthorised or erroneous opening.

Ventilation Fresh air supply and existing air discharge

Before starting and during work in containers, silos and confined spaces, ventilation must be used to ensure that no gases, vapors, mists or dusts in concentrations that are hazardous to health, as well as no explosive mixtures or lack of oxygen can occur.
A distinction is made between technical (artificial) and free (natural) ventilation.

Free ventilation, brought about by pressure or temperature differences, is only sufficient if the workplace limit values ​​or other relevant health-based limit values ​​are complied with and oxygen deficiency is excluded. This is especially true if small-scale work is carried out with small quantities, with substances with a low hazard potential, in rooms with large volumes
and there were no dangerous concentrations of hazardous substances or lack of oxygen in the container before work began.

The formation of an explosive atmosphere is considered to be prevented if it is permanently ensured that the concentration of gases, vapors, mists or dusts in the mixture with air is below 50% of the lower explosion limit. If non-atmospheric conditions exist, the changed safety parameters must be taken into account in order to assess the possible formation of explosive mixtures. The fresh air must be taken from the outside air or, if this is not feasible, from rooms whose air is free from harmful or flammable contaminants. These rooms must be connected to the outside air through large openings.

The air supply must be designed in such a way that the entire space in the container is flushed and the people work in the fresh air flow as far as possible.

Ventilation plan

A design sketch for the ventilation plan must be included in the safety assessment. This plan must show the supply and exhaust air and indicate the respective flow directions. Hazard sources, e.g. exhaust-generating devices and machines, must be marked in color and located in the ventilation plan. The ventilation plan must be signed by the safety officer and the person carrying out the work and also recorded in the Tool Box Talk.

Respiratory protection

The choice of respiratory protective equipment is the responsibility of the supervisor. Respiratory protection must be selected on the basis of the available data in such a way that a hazard can be completely ruled out. If no specific hazard data is available, the next safest respiratory protection system must be used. If the occurrence of hazardous substances in dangerous concentrations or quantities cannot be prevented by the measures specified in the regulations, respiratory protective equipment must be used when working in containers, silos and confined spaces.

When selecting a suitable respiratory protective device, its protection factor (multiple of the limit value) must be taken into account, see also DGUV Rule 112-190 “Use of respiratory protective devices”. The use of filtering devices is only permitted if it can be ensured that there is no risk of oxygen deficiency. If necessary, the oxygen concentration must be measured continuously and oxygen deficiency must be indicated by optical or acoustic warning devices, see also DGUV Rule 112-190 “Use of respiratory protective devices”.

Work in containers, silos and confined spaces with an oxygen content of less than 17% by volume may only be carried out using insulating equipment. If respiratory protection and personal fall protection equipment are used at the same time, both pieces of equipment must be used in such a way that they do not interfere with each other. Mutual interference can be avoided by using coordinated systems, e.g. harnesses with an integrated carrying device for compressed air cylinders.

The function of the breathing apparatus can be impaired by the impact, e.g. tearing off the hose or tearing off the breathing connection. To minimize this risk, when using respiratory protection and personal fall protection equipment at the same time, the attachment point and the setting of the connecting device must be selected so that the shortest possible fall arrest distance is effective.

The breathing air connection to the access technician must be equipped with redundancy. This must guarantee the access technician a breathing air supply of at least 30 minutes or three times the rescue time according to

Rescue documentation

Clearance measurement of containers, silos and confined spaces

As part of the safety assessment, it must be determined which substances and mixtures are contained in which concentration in the container, silo or confined space or can occur during the work and whether a lack of oxygen can occur. In most cases, clearance measurements are required for this. The measurements must be carried out at a representative location. The measurements must analytically represent air/foreign gas mixtures. In the case of dust, the number and size of particles must be measured and integrated into the safety assessment (selection of respiratory protection).

Suitable measuring methods are: continuous measurements, e.g. with direct-reading devices,

repeated individual measurements, e.g. with test tubes or with sampling and laboratory analysis.

Particle flow and particle analysis methods.

The conditions in the container, silo or confined space are also crucial for the selection of the measuring method. A distinction must be made between containers, silos and confined spaces:
that are completely emptied, rinsed and cleaned and into which the ingress of hazardous substances or nitrogen gases is excluded, that contain contaminants or residues that can release hazardous substances, that cannot be completely separated and into which the ingress of hazardous substances or nitrogen gases is therefore possible. In these cases, direct-reading measuring devices are preferable.

Only persons who have the required specialist knowledge may be commissioned to carry out free measurements.

The specialist knowledge relates to
the measuring devices or measuring methods used, the hazardous substances to be measured,
the operational conditions, e.g. the condition of the containers, silos and confined spaces, possible installations that may influence the sampling. In many cases, measurements are also taken continuously during the work after approval. This continuous monitoring by the security guard, e.g. with gas warning devices, does not require specialist knowledge in accordance with DGUV principle 313-002.

Protective measures against hazards due to oxygen deficiency

Hazards due to oxygen deficiency may exist if the oxygen concentration is lower than the oxygen content of the natural breathing air of 20.9% by volume. If the oxygen concentration is lower than 20.9% by volume, the cause of this must be measured and an assessment made as to whether there is a risk from foreign gases or hazardous substances.

This hazard can be caused by inertization systems, for example, and must be excluded in advance by safety measures in the safety assessment. If a guaranteed exclusion through redundant constructive safety measures is not possible, the work must be carried out with independent breathing air.

A hazard exists, for example, if the difference to the 20.9% oxygen by volume consists of hazardous substances and their workplace limit values or short-term values are exceeded. This refers to carbon dioxide, for example.

A hazard does not exist, for example, if the difference to the 20.9% oxygen by volume consists of nitrogen or noble gases and the oxygen content is a good 17%.
Even substances and stored goods that are not hazardous materials can cause a life-threatening drop in oxygen concentration in containers, silos and confined spaces due to oxygen depletion

Explosion protection measures

Avoiding the occurrence of an explosive atmosphere or explosive mixtures
The primary measure of explosion protection is to avoid the occurrence of hazardous explosive mixtures by taking measures in accordance with DGUV regulations or (see also TRGS 720 ff.).

For a detailed safety assessment, the explosion documentation must be included and taken into account in all cases. When working in containers, silos and confined spaces, non-atmospheric conditions may prevail, e.g. due to increased oxygen concentrations or the presence of other oxidizing agents. When determining the explosion protection measures, it must be taken into account that the safety-related parameters are changed under non-atmospheric conditions.

In many cases, the occurrence of an explosive atmosphere or an explosive mixture is difficult to assess.

These can arise, for example:

  • by residues released during cleaning work, wood dust, coal dust, plastic dust, organic dust (e.g. flour and sugar)
  • through work processes, e.g. welding gases, cleaning agents, with the aid of post-evaporation of flammable liquids from incrustations or impurities in a poorly cleaned container,
  • if, for operational reasons, flammable substances cannot be removed from the containers, silos or confined spaces,
  • by whirling up deposits of dusts with combustible components.

The formation of an explosive atmosphere is deemed to be avoided if it is permanently ensured that the concentration of gases, vapors, mists or dusts in a mixture with air is below 50 percent of the lower explosion limit.

The formation of an explosive atmosphere via vapors of a flammable liquid is avoided if the processing temperature of the liquid is below its lower explosion point (UEP).

Meanwhile, it must be accepted

  • that the ambient temperature can rise above the UEP (e.g. solar radiation),
  • that the flammable liquid can be heated above the UEP (e.g. using tank heating equipment).

This is the case for liquids consisting of only one component if the highest possible processing temperature is at least 5 K below the flash point, and for liquid mixtures if the highest possible processing temperature is a good 15 K below the flash point.

If a flammable liquid is sprayed or sprayed (e.g. paint spraying), aerosols are formed in the spray area. Separated from the above-mentioned conditions, these form a dangerous explosive concentration.

The formation of a hazardous explosive atmosphere based on aerosols is not to be expected if only non-flammable liquids are used.

Avoid ignition sources

If the presence of hazardous explosive atmospheres or hazardous explosive mixtures cannot be avoided for operational reasons, the occurrence of effective ignition sources must be consistently avoided in accordance with TRBS 2152 Part 3. External sources must also be considered in detail and taken into account. Sketches must be made of any external sources and marked locally. Permanent analyses and monitoring systems must be implemented and taken into account in the safety assessment.

For surface treatments in rooms and containers, TRGS 507 applies, which contains information on explosion protection measures and whose considerations on necessary ignition protection measures are helpful for the assessment of similar scenarios.
For temporary work in containers, silos and confined spaces, zoning in accordance with DGUV Rule 113-001 “Explosion protection rules” is not advisable, as the respective work areas require consistent compulsory measures.

Protective measures against electrical hazards

To provide qualitative protection against electrical accidents, at least one electrically trained person (EuP) should be integrated into an emergency team / task force. The consequences of electrical accidents are generally more serious than the average for all accidents at work. The proportion of fatal electrical accidents in terms of reportable electrical accidents, for example, is 20 times higher than the proportion of fatal work accidents in all reportable work accidents. It is therefore fundamental to consciously prevent electrical accidents with technical, organizational and personal measures.

Due to the characteristic properties of containers, silos and confined spaces (in particular access situation, material properties and freedom of movement inside), an increased electrical hazard can regularly be assumed (=> protective measures for limited freedom of movement in a conductive environment).

Electrical hazards can generally emanate from all live cables and electrical system components, such as switching and metering systems. These hazards must be accepted in the risk assessment to be drawn up by the contractor and corresponding protective measures must be defined.

The primary electrical hazards are the flow of current through the body and the risk of electric arcs. In the latter case, the resulting thermal radiation or contact with hot materials can cause damage.

If live components of electrical equipment are touched quickly or if the necessary safety distance is not maintained, a dangerous current flow from the human body can occur. Just one approach can be enough to cause a flashover and electricity to flow through the human body.

This current flow can damage the internal organs and their functionality. For example, a current flowing through the body can disable the body’s own muscle control systems, heart activity and breathing. The degree of damage is determined by the current strength, the time interval of the current flow, the current path in the body and the frequency of the current.

Measures to protect against falling

All measures against falls from a height must be taken thoroughly and redundantly. If there is a risk of falling when working in containers, silos and confined spaces, suitable measures must be taken to protect against falls.

Due to the particular dangers of working in containers, silos and confined spaces, protective measures against falls from a height may be necessary even at low heights. On the one hand, the risk of falling may be increased (e.g. due to contamination of vertical ladders), and on the other hand, the consequences of injury may be more serious due to limited rescue options. In this case, suitable safety and risk reduction measures must be taken in advance.

The use of rope ladders or similar aids is generally prohibited, as they no longer correspond to the current state of the art.

If technical measures against falls from a height are not possible due to local or spatial conditions, personal fall protection equipment must be used.

The required anchorage points and the personal protective equipment to be used must be determined and documented by the SZP supervisor.

Protective measures against sinking or spilling

Before starting work, it must always be ensured that the filling and removal equipment is switched off and secured against unintentional and unauthorized activation. Furthermore, these systems must be structurally secured. The securing must be documented in writing.

Bulk storage facilities may only be entered without securing if hazards due to sinking or crushing in the bulk material or due to the removal device are excluded. This would be, for example, accessible silo frames or silo systems that can be entered through doors or bulkheads and are fully visible. In this case, attention must be paid to the material walls, which must be removed from above in advance, verified and documented. It is generally advisable to inspect and document the interior of the silo outside the danger zone before an unsecured inspection.

If a guaranteed inspection is not possible, a concealed hazard must be assumed.

Protective measures against health hazards due to increased physical stress

Possible physical strain must be recorded in the safety documentation and risk assessment and taken into account in all cases. Working in confined spaces is in itself a high physical strain. Additional strain, e.g. through the use of personal protective equipment, work equipment, difficult access, high or low temperatures and heavy transportation work, should be avoided wherever possible.

Working at high temperatures in particular poses an increased risk in summer. It is the responsibility of the supervisor to determine whether a load is tolerable. In doing so, it is not only the access technician’s physical limit of exertion that must be taken into account, but also the general level of exertion of an untrained person. The use of respiratory protection when working in containers, silos and confined spaces should be the exception. Beforehand, all possible measures should be taken in accordance with the regulations to ensure that the breathing air is of sufficient quality so that the use of respiratory protective equipment is not necessary.

The access points and, if necessary, the descents into the containers, silos and confined spaces should be designed in such a way that the work areas can be reached without major physical exertion.

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