Penal Code Section 4502, subdivision (a) provides in pertinent part: "Every person who, while at or confined in any penal institution ... possesses or carries upon his or her person or has under his or her custody or control any instrument or weapon of the kind commonly known as a blackjack, slungshot, billy, sandclub, sandbag, or metal knuckles, any explosive substance, or fixed ammunition, any dirk or dagger or sharp instrument, any pistol, revolver, or other firearm, or any tear gas or tear gas weapon, is guilty of a felony ...." Section 4502, subdivision (a) is intended to protect inmates and correctional staff from assaults with dangerous weapons by prisoners. (People v. Custodio (1999) 73 Cal.App.4th 807, 812.) It was "adopted on the justifiable theory that there is greater danger of imprisoned felons becoming incorrigible and resorting to violence if they are permitted to carry upon their persons deadly weapons." (People v. Wells (1945) 68 Cal. App. 2d 476, 481.) The statute "applies to instruments that can be used to inflict injury and that are not necessary for an inmate to have in the inmate's possession." (Custodio, supra, at p. 812.) "The fact that the Legislature has made the possession of any weapon, not just firearms, in a penal institution felony is indicative of the danger weapons present in such a facility." (People v. Brown (2000) 82 Cal.App.4th 736, 739-740.) Accordingly, section 4502 "absolutely prohibits all prisoners in any state prison, without qualification, from possessing or carrying on their persons certain designated deadly weapons. The intention with which the weapon is carried on the person is not made an element of the offense. Proof of the possession of the prohibited weapon infers that it is carried in violation of the statute." (People v. Wells, supra, 68 Cal. App. 2d at p. 481.) "Although criminal statutes are not often construed to impose sanctions in the absence of mens rea or guilty intent, an exception occurs where the statute is an expression of a legislative policy to be served by strict liability. Section 4502 of the Penal Code serves an objective demanding relative inflexibility and relatively strict liability. Its objective is protection of inmates and prison officials against assaults by armed prisoners. It is one of the 'stringent statutes governing prison safety.' Its purpose would be frustrated were prisoners allowed to arm themselves in proclaimed or actual fear of anticipated attack by other inmates. Thus a group of California decisions place section 4502 among the statutes whose violation does not depend upon proof of guilty intent, holding that its prohibition is absolute; that it is enough to show the defendant's knowing possession of the forbidden weapon; that his purpose of arming himself for self-defense against an anticipated assault is no defense." (People v. Wells (1968) 261 Cal. App. 2d 468, 478-479, 68 Cal. Rptr. 400, disapproved on other grounds in People v. Barnum (2003) 29 Cal.4th 1210, 1219, fn. 1.) In order to prove a violation of section 4502, subdivision (a), the prosecution must prove the defendant was confined in a state prison and knew the prohibited object was in his or her possession. (People v. Reynolds (1988) 205 Cal. App. 3d 776, 779, overruled on other grounds in People v. Flood (1998) 18 Cal.4th 470, 490, fn. 12; People v. Strunk (1995) 31 Cal.App.4th 265.) "Proof of knowing possession of such an instrument by a state prison inmate is sufficient for conviction. The prosecution is not required to prove the intent or purpose for which the instrument is so possessed. " (People v. Steely (1968) 266 Cal. App. 2d 591, 594; People v. Reynolds, supra, at p. 779.)