May I ask what height or diameter a device must have to require a straight ladder, and what height requires a spiral staircase? Are there any standard regulations...

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I remember that there is no requirement for this; as long as there are valves at the top of your equipment that need to be operated (which cannot be operated directly from the ground or using a platform), or instruments that need to be checked and cannot be seen clearly from the ground, then a ladder needs to be installed.

Large equipment! How can you go up without a framed ladder platform?

View the design specifications for tower-type containers and steel chemical processing containers

Straight ladders or spiral ladders are both pathways used to reach the top of equipment for operation or maintenance; there are no strict standard specifications for them. Refer to the 02R112 dome tank atlas: straight ladders are used for 40m3 tanks (with a diameter of 3.6m and a height of 4.8m), while spiral ladders are used for tanks of 60m3 or larger (with a diameter of 4.2m and a height of 5.25m) ； However, for slender tower-type equipment, the straight ladder + intermediate platform design is basically used.

I haven’t heard that ladders are necessary for very large heights. Whether to install a ladder, and what type of ladder to use, is determined based on factors such as whether operations need to be carried out on the top of the tank, the frequency of these operations, and the company’s requirements regarding ladder design. Small tanks usually have straight ladders; those with a capacity of 500 cubic meters or less tend to have straight ladders. Large storage tanks generally have spiral ladders, though some also have straight ladders. Straight elevators generally reach a maximum height of 10m.

Code for Design of Oil Storage Tanks (GB50074-2014), Section 6.4 Tank Accessories, 6.4.1 Vertical storage tanks shall be equipped with ladders, platforms, and handrails at the top of the tank. Vertical storage tanks with a height greater than 5m should be equipped with spiral ladders.

To be honest, there’s no clear standard for this thing, and besides, it’s not possible to establish standards at such a detailed level. Generally, spiral ladders are not installed in towers. Although the diameter of towers is increasing these days, spiral ladders are still not used; this is because towers are usually very tall, and a platform needs to be provided for each access point. It is difficult to accommodate all these access points with a spiral ladder, and sometimes when the access points are close together, it is impossible to use one. Additionally, there are many external pipe openings on the tower, as well as associated pipelines and valve assemblies; in such cases, ladders are not sufficient to meet the requirements. Generally, large storage tanks are equipped with spiral ladders, mainly because there are usually valves or other accessories at the top of the tank. Spiral ladders make it easier for people to carry tools up and down, so they are more convenient for operation. As for the size at which spiral ladders should be used, it depends on the circumstances – it’s really hard to determine; many factors come into play. It depends on the operational requirements, existing habits, and in some cases, people even consider spiral ladders to be expensive. It’s difficult to give a general answer.

If there are no valves or other mechanisms for operation on the tank, is it unnecessary to install a ladder?

Generally, it’s not possible; even if there is nothing to do on the top of the tank, it may still have insulation, paint on it, or require regular inspections. In any case, it’s necessary to go up to the top of the tank. If the frequency of access is very low, a straight ladder can be considered.