Employees must often enter vessels and other confined spaces in order to perform maintenance, repair and inspection tasks. The openings of tanks, pressure vessels, sewer shafts and wind turbine blades are however often so small that although they permit access, they make the rescue of injured persons from them difficult, if not impossible. Resolving this problem is above all a task for standardization.
During work in vessels and confined spaces, a lack of oxygen and an acute risk of exposure to hazardous substances present a much greater hazard than is the case at normal workplaces. Rescue in the event of an emergency is however exceptionally difficult, since some standards and specifications governing vessel openings (such as EN 12953, Shell boilers; DIN 28136, Agitator vessels; and AD-2000 code of practice A5 [The AD 2000 codes of practice are drawn up by the AD working group responsible for pressure vessels, and support all essential safety requirements of the 97/23/EU European Pressure Equipment Directive] governing openings of pressure vessels) specify minimum dimensions that are too small. Practical exercises have shown rescue to be impossible with opening dimensions of 300 mm × 400 mm or 320 mm × 420 mm. In order to enter the vessel, a person must "thread" themselves through an oval manhole (see image on page 13). An unconscious person cannot be transported through this opening, however.
The angled arrangement of the openings also causes problems during rescue operations. An unconscious person in the rescue system always hangs vertically; owing to the manhole being at an angle, the available width is severely reduced (see image on page 14). In the interests of better access and rapid rescue, these openings should therefore always be horizontal. Where no facility is provided for the attachment of rescue equipment above the manhole, it can be secured directly to the flange of the access opening.This, again, is possible only on a horizontal opening.
In the German body of regulations, BG Rule (BGR) 117 Part 1 governing work in vessels, silos and confined spaces (pdf, in german) recommends minimum dimensions that are sufficiently large to enable a person to be rescued through them. The recommended size of the openings depends upon a number of factors: location and accessibility of the access opening; clearance above, in front of or below the opening; the use of personal protective equipment (e.g. respiratory protection, PPE for rescue, PPE for protection against falls from a height); the use of work platforms or access equipment; wall thicknesses and the neck height.
If a person cannot be rescued swiftly and harmlessly through a manhole, BGR 117-1 requires the vessel to be opened by means of equipment that must be specially kept available for the purpose. In the case of pressure vessels, the possibilities for this are limited owing to their wall thickness; in addition, it would result in destruction of the vessel.
Problems associated with rescue are not apparent beforehand
The recommendations of the BGR are intended not for manufacturers, but solely to assist operators in selecting vessels for purchase. Operators however are generally concerned in the first instance with cost and with compliance of the design with the standards. They do not realize at this stage that whilst the vessel that they are purchasing may comply with the standards, it will cause them difficulties later on.
Boilers and pressure vessels are tested prior to commissioning. The authorized inspection body tests the vessel solely for compliance with the technical rules and standards in accordance with the German Ordinance on industrial safety and health. Consequently, vessels constructed and licensed routinely in a proper procedure fail to comply with the body of regulations of the German Social Accident Insurance Institutions and present a considerable hazard to the persons working within them.
Provision for wider openings in standards In Germany, fire-tube boilers alone account for an estimated 20,000 boilers that must be inspected every five years. This means that on average, 20 people enter a boiler every day without their rescue being assured.
Modern access and rescue procedures require a rethink among standards developers and manufacturers regarding the design of access openings. The "Vessels and confined spaces" subcommittee within the "Raw materials and chemical industry" expert committee of the DGUV has involved KAN in order to ensure that larger minimum dimensions for access openings are set out in the standards and the AD-2000 codes of practice. In addition, the attention of future operators of the vessels is to be drawn to the issue by means of suitable publications.
Dipl.-Ing. Rainer Schubert