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OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at

July 29, 2010

Letter #20090606-9097

Re:  Whether OSHA prohibits the use of a double S-bend elbow ("Rams Horn") shut-off valve at the end of a concrete pumping hose.

Question:  Does OSHA prohibit the use of a Double S-bend Elbow (a/k/a "Rams Horn") shut-off valve at the end of a concrete pumping hose?1

Answer: Title 29 CFR 1926, Subpart Q, addresses concrete pumping.  Section 1926.702(e) provides the requirements for concrete pumping systems as follows:

  1. Concrete pumping systems using discharge pipes shall be provided with pipe supports designed for 100 percent overload.
  2. Compressed air hoses used on concrete pumping system shall be provided with positive fail-safe joint connectors to prevent separation of sections when pressurized.

This section does not explicitly prohibit the use of a double S-bend elbow shut-off valve at the end of a delivery hose.

However, § 5(a)(1) of the OSH Act requires employers to "furnish to each of his employees employment and a place of employment which are free from recognized hazards ...."  Construction work-practices that are prohibited by a consensus standard typically provide evidence of a recognized hazard.  Notably, neither ASME B30.27-2009 § 27-1.102 or ACI 304.2R-96, chapter 3.63, prohibit the use of a double S-bend elbow shut-off valve at the end of a delivery hose.

Your incoming letter attached an opinion from the American Concrete Pumping Association (ACPA), which stated, "the ACPA does NOT recommend the use of either [a double "S-bend" elbow] or a double-ended discharge hose."  According to the ACPA, a double S-bend elbow is unsafe because, in the event of hose-whipping, the shear weight and mass of this shut-off valve can cause serious harm if it strikes a person.  Although hose-whipping is a hazard associated with concrete pumping, there are recognized safe work practices that protect employees from this hazard.  These recognized work practices are unrelated to the type of shut-off valve used.  For example, § 27-1.9 of ASME B30.27-2009 provides that "[t]he horizontal slewing speed at the end of the boom shall not exceed 5 ft/sec (1.5 m/s)."  Operating a concrete pump in accordance with § 27-1.9 of ASME B30.27-2009 is just one example of a recognized work practice that protects employees from hose-whipping.

Nevertheless, even where the safe work practices described above are used by employees, there may be scenarios where employees may still be exposed to the hazard of hose-whipping as a result of a concrete pump's design or configuration.  In these cases, OSHA will examine how the concrete pump is configured to determine whether the use of a double S-bend elbow creates a recognized hazard to employees.  Employers may, for example, mitigate the hazard of hose-whipping from a double S-bend elbow by keeping the double S-bend elbow shut-off valve elevated above employees' heads and attaching a single-ended discharge hose for employees to handle, while pouring concrete as suggested by ACPA.4


Ben Bare, Acting Director
Directorate of Construction

1  Your question originally focused on the permissible uses of a product you have a patent for, but after talking with you on the phone you clarified that you were inquiring about any Double S-bend Elbow shut-off valve. [back to text]

2  Section 27-1.10.2(a)(3) most directly addresses the standards for valves.  This section requires valves to meet a minimum ratio of 2:1 in burst pressure versus working pressure. [back to text]

3  Section 3.6.1 addresses "shut-off" valves as follows:

Valves -- Several types of valves are currently manufactured for concrete pipelines.  Manually or hydraulically operated valves are available for three basic functions.  Manufacturers' recommendations for appropriate location and pressure limitations must be followed.

Shut-off - This type of valve stops the flow of concrete within the placing system.  These valves are useful for holding a "head" of concrete in a vertical standpipe and come in a wide range of internal pressure ratings.  Shut-off valves may be of the "spade," "gate," or "pin" variety.  All of these valves restrict the flow of concrete by the insertion of a blocking member in the valve body. [back to text]

4  The ACPA also stated several other alternatives to using a double S-bend elbow: (1) boom configurations that minimize vertical drops; (2) the use of a reducing end hose; (3) the use of a steel reducer between the boom tip and the end hose.  The alternatives mentioned by ACPA are not the only means of eliminating or mitigating the hazard of hose-whip with a double S-bend elbow. [back to text]